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THE

EOWEHE SILURIAN LAMELLIBRANCHIATA

MINNESOTA

By E. O. ULRICH

[FROM VOL. III OF THE FINAL REPORT OF THE GEOLOGICAL AND NATURAL HISTORY SURVEY OF MINNESU'T

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QGHAPTHR VI. LIBRARIES

THE LOWER SILURIAN LAMELLIBRANCHIATA
OF MINNESOTA.

BY E. O. ULRICH.

A number of names for this class of mollusks, commonly known as mussels,
have, from time to time, been proposed, but none of them, save Blainville’s Lamelli-
branchiata, which, on the whole, is an appropriate designation, has enjoyed more
than merely temporary popularity. Of the other names, that proposed by Goldfuss
in 1820, Pelecypoda, alone presents fair claims to recognition, since its adoption would
produce that most desirable element, uniformity, in the terminology of the various
classes comprised in the subkingdom Mollusca. Blainville’s name, however, has six
years’ priority, and is so well established in literature that it is doubtful if the con-
fusion which would result from a change of names would be sufficiently compensated
for by the superior advantages of Goldfuss’ term.

The Lamellibranchiata agree with the Brachiopoda in having bivalved shells,
but differ in having them, as a rule, equal and inequilateral instead of inequivalved
and equilateral; they are, furthermore, placed on the sides of the animal (for which
reason we distinguish them as right and /eft), instead of above (dorsal) and below
(ventral). From the Gastropoda and Cephalopoda they are distinguished by wanting
a distinct head, in having bivalved shells, a bilobed mantle and lamelliform gills
developed in pairs.

Generally the animal is symmetrically developed, of oval, rounded or trans-
versely elongate form, laterally compressed and enclosed in the two fleshy, often
more or less united, lobes of the mantle. Within the latter, which are attached to
and secrete the calcareous or perlaceous valves, we have first the lamelliform gills,
and between these the various internal organs, such as the heart, intestines and
organs of generation, and the mouth and anal opening, and usually also a protrusible
muscular foot. Numerous modifications of the mantle lobes occur. Sometimes they
are separate, at other times their margins are grown together so as to enclose the
animal as in a sack. In the latter case an opening is left in front for the protrusion

[475]

476 THE PALEONTOLOGY OF MINNESOTA.

(Lamellibranchiata.

of the foot, and another in the back serving for beth the inhalation of water and the
expulsion of the excrements. The posterior opening may be further modified so as
to form two more or less distinct tubes or siphons, and these may be retractible or
of such size and consistency that they project permanently through the gaping
posterior margin of the shell. In most instances the siphons are capable of being
completely or partially retracted, and the line of attachment of the muscles of the
mantle producing this retraction is bent inward more or less decidedly. When such
an inbending of the pallial line (as the attachment of the mantle to the inner surface
of the shell is called) is found in fossil shells the inference is regarded as conclusive
that the animal possessed retractile siphons. When, on the other hand, the pallial
line is simple (7. e., without a sinus) we are obliged to conclude that the siphons were
either very small or wanting entirely.

The foot—a perfectly retractile organ, presumably of locomotion—lies in the
anterior part of the shell between the gills and mantle lobes. Its form is various,
but commonly compressed, hatchet or club-shaped, and the muscles which produce
and regulate its action are attached usually above or behind the anterior adductor.
Not infrequently chitinous threads spring from the lower side of the foot. When
these are developed in sufficient number to form a bundle or byssus, the shells may
thereby attach themselves to foreign bodies, and in such cases the anterior margins
of the valves do not close tightly, but leave what is known as the byssal opening.
Among paleozoic representatives of this class the Ambonychiide afford the best
instances of shells with a byssal opening.

Of all the organs of the animal none are of greater importance to the paleon-
tologist than the strong muscles (adductors) which serve to close the valves. There
may be only one, the posterior, as in the recent oyster, or of the two the anterior
one may be disproportionately small. In the majority of cases, however, the two
muscles are approximately of equal size. Other and much smaller muscular scars
may be noticed, especially in the umbonal cavity. which were produced by muscles
which partially supported the movements of the gills and palpi and, as already stated,
of the foot.

The shell in which the interest of the paleontologist is chiefly centered consists
largely of two layers, the outer, secreted by the thickened margin of the mantle,
being composed of vertically arranged prismatic cells filled with calcite, the inner of
structureless thin parallel leaves. Generally a delicate chitinous epidermis is spread
over the cellulose layer. Growth of the valves begins at the apex or beak, a more
or less prominent point situated almost invariably somewhere along the anterior
half of the hinge margin. Further increase takes place principally at the periphery,
producing, when the edges of the mantle are entire, a simple, more or less regularly

BRACHIOPODA. 477

Terminology.]

concentric, striation (growth lines) of the surface. But when the mantle edges are
undulating or dentate the concentric growth lines are crossed by radiating striz or
plications.

The various parts of the shell are conveniently brought out and illustrated in
the following section on terminology.

TERMINOLOGY.

Outline: The designation of the various parts of the outline depends upon the
position in which the shell is placed. I shall adopt, because it is certainly the
most convenient if not always the most natural position, the one in which
the beaks are placed uppermost and the hinge line nearly or quite horizontal.
The part in front of the beaks, toward which they are usually inclined, is
therefore considered as the anterior end, while that behind them, often much
the largest and widest, is the posterior. The upper edge is known as the
cardinal or dorsal margin, while the lower is called the basal or ventral.

Dimensions: The length as given in the following pages always expresses the distance
between the most prominent points (extremities) on the anterior and posterior

Fig. 35. I and II, right valves of IscHYRODONTA (?) OVALIS Ulrich and MATHERIA RUGOSA Ulrich,
lettered and divided by lines to illustrate the section on outline and dimensions. A-—B, length; C-D,
anterior hight; E-F, posterior hight; a 6, dorsal or cardinal margin: e d, anterior end and margin; e f,
basal or ventral margin; g h, posterior end and margin.

III, antero-cardinal view of a small specimen of Cuneamya curta Whitfield, from the upper part of
the Cincinnati group of Ohio; uw, umbones and beginning of umbonal ridges; e, escutcheon; /, lunule.

IV, the two valves of an undescribed species of Orthodesma lying open in the shale and showing the
ligament at 7; middle beds of the Cincinnati group at Cincinnati. ¢_.,,. Pe

V, dorsal view of an entire cast of the interior of Chenodomers typrcnies, a new genus and species
from the upper beds of the Cincinnati group of Ohio, showing a shell gaping at both ends.

VI, anterior view of Byssonychia radiata (Ambonychia radiata Hall), illustrating a shell with a
byssal Opening. This specimen is from Cincinnati, Ohio, and is peculiar in having the right valve (left
side of figure) preserved as a cast of the exterior and the left valve as a cast of the interior. In the latter
is shown the pallial line (at p) running along the anterior side to a point under the beak.

478 THE PALEONTOLOGY OF MINNESOTA.
{Termiology.

margins. This line may be parallel with the hinge, but more commonly
diverges more or less strongly posteriorly. The hight is given in one or two
measurements; the former, when the shell is approximately equilateral (as in
many species of Tellinomya) or elliptical in form (Clidophorus) with the greatest
hight subcentral or beneath the beaks; the latter, when the shell is elongate
or has one end much wider than the other (Orthodesma and Modiolopsis). “In
such cases two lines are drawn at right angles with the hinge line, one from
the beaks to the ventral margin, the interval between the two points being
the anterior hight, the other across the posterior end, from the posterior
extremity of the hinge, giving the posterior hight. By thickness is understood
the shortest distance between the points of greatest convexity of the valves.

Area or Escutcheon: A variously shaped, usually elongate, inflection of the dorsal
edge, generally longitudinally lineate, and serving as a receptacle for the
ligament. When the area is restricted to posterior to the beaks, as in

_ Cuneamya, it is, strictly speaking, to be called an escutcheon.

Inunule: A similar, but shorter and commonly heart-shaped inflection or distin-
guishable area in front of or beneath the beaks. Cuneamya offers good
examples,

Gaping and closed shells: The valves fit either closely all around or they may fail
to do so and gape at one or both ends, and sometimes ventrally.

Byssal opening: A small, distinctly modified portion of the. anterior margin, through
which the byssus protruded. Among the paleozoic types the Ambonychiide
furnish the best examples.

Beak: A more or less prominent point on each valve, usually bending forward and
overhanging, in a variable degree, the dorsal edge. It marks the point at
which growth began, and generally is situated anterior to the center of the
valves. Many species of Te/linomya, Nucula and Clinopistha afford exceptions
to the last rule.

Umbones: The use of this term, which is generally applied in a sense synonymous
with beaks, is here restricted to the gibbous rostral portion of valves in which -
the beaks are incurved over the hinge line and invisible in a side view.

Umbonal ridge: A more or less strongly rounded or angular ridge-like prominence,
extending from the beaks or umbones toward the posterior extremity of the
shell. Example, Whitella.

Cardinal or dorsal slope: Generally applies to the flattened or concave declivity
from the umbonal ridge to the dorsal edge posterior to the beaks, When
the declivity on the anterior side is sufficient to be noted it is designated. as
the anterior cardinal slope.

BRACHIOPODA. 479

Terminology.)

Anterior, posterior and ventral slopes are self-explanatory terms.

External ligament: An elastic, horny band, of variable length, serving to hold the
valves in position, and situated invariably over the dorsal edges close behind
or under the beaks. But rarely preserved in fossil shells.

Internal ligament or cartilage: This is generally of cartilaginous consistency, and
often but a modification or extension of the external ligament. In the latter
case it lies along the posterior inner border of the hinge, where its presence
may be indicated by linear thickened supports which, in casts of the interior,
may sometimes be confounded with impressions of lateral teeth, (Whitella).
A true internal cartilage, usually occupying a small pit beneath the beaks
(Fig. 36, III and VID), is found in Nueula, Pecten and many other types of the
secondary and more recent rocks, but is rather rare among paleozoic species.

Fig. 36. Illustrating Hinge Types, Muscles and Pallial Impressions.

land II, interior of a right valve of Lyrodesma major Ulrich, of the natural size, and the rostral
portion of the valve x 2; upper beds of the Cincinnati group of Ohio.

III, hinge of a species of Nuculana, showing internal cartilage pit atc.

IV, interior of a left valve of Vanuxemia hayniana Safford, sp., from the upper Trenton limestone of
central Kentucky; a, area; c. t., cardinal teeth; J. ¢t., posterior lateral teeth; a. a., anterior adductor, and
p. 4., posterior adductor impression: p., pallial line. era Ubich

V, cast of the interior of a left valve of an-ennamed—variety-of Byssonychia radiata-Hel, sp.
(Ambonychia bellistriata Miller and others, not Hall, 1847,) from the lower beds of the Cincinnati group of
Ohio. In this specimen the posterior adductor impression (p. a.) and the pallial line are,usually distinct.

VI, a sharply defined cast of the interior of Lyrodesma major Ulrich (see also I and II), showing the
muscular impressions in a very satisfactory manner; a. a., anterior adductors; p. a., posterior adductors;
p. m., two pairs of pedal muscles.

VII, interior of a shell with a strongly sinuate pallial line (s), and an internal ligament pit (c);
Lutraria elliptica Roissy, Pliocene, Rhodus (one-half nat. size). The outline of this shell is to be noted in
connection with Fig. 34, I and II. k

VIII, undetermined species of Clidoporus, showing clavicle (cl. ).

Hinge teeth: This term applies to the teeth in general, but more especially when
these are numerous and subequal, as in “T’e/linomya.

480 THE PALEON'TOLOGY OF MINNESOTA.

[Preservation and methods of study.

Cardinal teeth: Refers to the teeth situated on the hinge in the region of the
beaks.

Lateral teeth: One or more, generally elongate, subhorizontal teeth or interlocking
ridges, often situated at the posterior extremity of the hinge.’

Muscular impressions: That of the anterior adductor, when present, is situated near
the margin in the antero-cardinal region. It may be as large or much
smaller than the posterior adductor, which, when both are present, is placed
at some point in the postero-cardinal region. When only one adductor scar >
is present (Monomyaria), or the anterior one is much the smaller of the two
(Heteromyaria), the posterior scar is situated nearer the center of the valve.
Umbonal scars are small impressions in the umbonal cavity, while the pedal
muscles often leave small scars above and behind the anterior adductor
impressions.

Pallial line: This is a more or less sharply defined line running nearly parallel with
the free margins of the valves and connecting the two adductor scars. Among
paleozoic representatives of the class the line is usually simple, but among more
recent forms a sinuate pallial line (said of it when its posterior part is bent
more or less strongly inward), is quite common.

Clavicle: A thin plate or ridge in each valve, of varying length, extending from the
hinge margin, immediately in front of the beaks, vertically downward, or

curving slightly forward. Example, Clidophorus.

PRESERVATION AND Merruops or Srupy.

In common with the Gastropoda, and probably for the same reasons, the paleo-
zoic Lamellibranchiata are oftenest found in the condition of casts of the interior.
This is true, especially of specimens preserved in dolomitic limestones like those of
the lower Trenton and Galena in Minnesota, Wisconsin and Illinois, and the Niagara
of northern Illinois and Wisconsin. These dolomitic specimens are to be regarded
as in a favorable state of preservation so far as study is concerned. The shell,
though dissolved away, has left good moulds of both the exterior and interior in the
matrix, so that with the aid of plastic gutta percha the student is enabled to produce
counterfeits of the shell that for purposes of classfication are scarcely to be excelled.
To make good impressions it is often necessary to clean the moulds of the small
crystals and other foreign matter that may in part occupy the space originally filled
by the shell. Unfortunately, collectors too often are careless in preserving the
outer mould, believing it, perhaps, of little consequence. In the interests of paleon-
tology I would recommend greater caution and a lessening of the number of frag-
ments by an early application of the contents of the glue pot.

LAMELLIBRANCHIATA. 481

Preservation and methods of study.

Good casts of the interior are also to be met with in shaly rocks, indeed, most
excellent ones when the shales are arenaceous. In soft shales, like those of the
Cincinnati group of Ohio, they are generally preserved as partial moulds of the
exterior. The approximately unaltered shell is to be counted as rare in lower
paleozoic formations when compared with their frequent occurrence in Carbonif-
erous deposits.

The most favorable method of preservation, so far as Lower Silurian material is
concerned, is that in which the originally calcareous shell is more or less completely
replaced by silica. Such specimens are rare in the Northwest, but common in the
solid limestones of the Trenton in Tennessee and Kentucky, and in the Black River
limestone of Canada. Beautiful specimens of this kind are to be found weathered
out, or blocks of the limestone may be treated with dilute acid with the same result.

The first essential in the study of fossil Lamellibranchiata is to determine
whether or not the material, as it lies before us, has retained its original form.
Distortion through pressure in the rock matrix is a most fruitful source of error
and one that even the greatest experience cannot entirely negative. It is evident
that the softer and, consequently, the more yielding the character of the matrix, the
greater the degree of the distortion. It is least in limestones and dolomites and
greatest in shales and slates. The direction of the distortion depends upon the
position occupied by the shell with respect to the bed planes of the enclosing rock.

Fig. 37. Illustrating distortion of shells through pressure. a, right side of a specimen of Modiolopsis
modiolaris Conrad, the hight of which has been reduced, as Shown in outline, to less than half what it was
originally. b, a shell of the same species greatly compressed lengthwise. c, the shell of an undescribed
species of Cuneamya, from Ohio, illustrating the effect of pressure on shells occupying an oblique position
in the shales. The line s-b indicates the plane of the strata and sea bottom. (See fig. 38.)

The exceedingly diverse results of the pressure, especially in specimens from shale,

are most puzzling to the beginner. Ifa shell happened to stand upon end, its length
-31

482 THE PALEON'TOLOGY OF MINNESOTA.

[Preservation and methods of study.

will be greatly reduced; if upon its base, the hight; if upon its side, the thickness.
When these positions were in no wise oblique, the beginner may fail entirely to
notice the distortion, which, when their position in the strata is oblique to the plane
of deposit, will be more or less clearly obvious to him because of the unsymmetrical
forms of the two valves. A careful examination. however, will reveal, at any rate
on specimens that have not been much weathered, certain fine parallel lines on the
sides of the crushed shell. These lines are coincident with and probably produced by
the deposit lamin of the matrix, and an experienced student may, with their aid, at
once determine the direction and perhaps the amount of the reduction of the par-
ticular dimension affected. It is to be remembered that the pressure under which
the fossils suffer acts, except in comparatively rare instances, in a vertical direction
only. Complete shells are generally compressed more or less obliquely, for the simple
reason that after the death of the animal the natural position of the shell, with
respect to the plane of the sea bottom, must be approximately as shown in fig. 37, ¢.
For the same natural cause, the disunited valves are better calculated to preserve
the original outline, because they are most likely to le upon their inner edges, the
latter being, therefore, at right angles to the direction of the pressure; in which
case, under ordinary circumstances, the only dimension that can be altered is the
thickness, this being reduced according to the amount of compression sustained by
the surrounding rock.

=iee
we

Fig. 38. Illustrating how to obtain a restoration of an obliquely compressed shell. The inner ontline
represents the specimen as it is now (see fig. 36-c), the outer one a restoration of its original form, S-B.
plane of sea bottom; d.—p., direction of compressing?force.

In making the restoration shown in fig. 38, only the two regions or points
a and b can be assumed as having retained their positions on the original boundary,
because there alone the outline of the shell coincides with the direction of the com-
pressing force. The only effect the latter could have had upon them was to increase
their convexity and to press them down slightly beneath their original positions.
On all other points, however, the effect was a reduction in the convexity of the

BR ey reise eae LAMELLIBRANCHIATA. 453
outline and consequently of the size of the specimen. The rostral region of the
right valve was greatly reduced and flattened, that of the left not so much reduced
and made more strongly convex at a. In the lower half of the shell the result of
distortion was reversed in the two valves. In the restoration, assuming the two
valves to have been equal, we draw a curve through the point a that is intermediate
in convexity between the flattened curve of the rostral half of the right valve and
the sharpened one of the left. An equivalent curve is then drawn for the right
valve and then continued to and beyond the point 4. We now have the original
outline of one of the valves as it would appear in an end view. The outline of the
other valve being equally curved, only in an opposite direction, is then easily
finished.

Having satisfied ourselves as to the original shape of the shell, it is first desirable
to determine whether the valves are equal, as In Modiolopsis and Whitella, or unequal,
as in Pterinea and Aristerella. Next we note the relation of the various parts of the
outline to each other, the relative width of the two ends and other features bearing
upon the determination of the contour. Now the position, altitude and degree of
fulness of the beaks and umbones is taken into account. The former may be terminal
(i. e., situated at the anterior extremity of the hinge line and projecting as far forward
as the margin beneath them), as in Ambonychia; or they may be nearly central in
position, as in some species of Ctenodonta. Then the umbones may be strongly
gibbous and the beaks curve over the hinge line (Cuneamya, Whitella), or they may
be less full and comparatively erect (Clionychia), or depressed, or scarcely distinguish-
able (Cycloconcha and Clidophorus). Decided deviations in the position and altitude
of the beaks are generally of generic value, but lesser modifications are likely to
prove of merely specific importance. The character of the surface markings will
probably have been taken into account at once.

In the next order, and here we usually credit them with generic and greater
value, the student should observe the presence or absence of a byssal opening, of the
lunule and escutcheon, and the character of the area. He should note also whether
the edges of the valves fit tightly or gape at one or both ends or ventrally. His next
step is to observe the position, distinctness and relative size of the various muscular
impressions, the adductors particularly. Nor is he to forget to trace out the pallial
line. Next he may find internal sockets, plates or ridges, that supported internal
ligaments, or to which muscles were attached. Finally, he will observe the method
of hingement. The hinge may be edentulous, in which case an external ligament
(perhaps internal also) may usually be assumed if not found (see fig. 35, IV). In
Modiolopsis there may be a slight thickening or rudimentary cardinal tooth in each

484 THE PALEONTOLOGY OF MINNESOTA.

(Classification

valve beneath the beaks, in Matheria there are two in the left and one in the right, in
Cypricardites three or more, and these are added to by the development of lateral
teeth (fig. 36, [V); some types may have radiating teeth (fig. 36, I and II); in others
the whole hinge margin will be divided transversely into numerous small teeth, while
still others may present a combination of short transverse and long lateral teeth. On
the whole, after giving due consideration to other pecularities, modifications in the
structure of the hinge are to be ranked as of the highest importance.

CLASSIFICATION. Z

The class Lamellibrachiata, or Pelecypoda, is variously divided by authorities.
It is neither necessary nor desirable that the numerous systems should be considered
here, since it is my impression, and here I merely follow the opinions of some of our
latest and highest authorities, that they are all more or less misleading and inade-
quate. The fact is, we have not yet arrived at that stage in knowledge where a
really natural classification is possible. Too little of the paleozoic representatives
of the class is known well, and until more is learned of the evolution of the recent
types from their fossil ancestors no attempt is likely to prove more than provisional.
What we want now are facts and when sufficient of them have accumulated I doubt
not the desired natural scheme of classification will evolve itself.

Still, since we have systems, they may as well be used till something better is
furnished. Of course, only paleozoic types are here considered, and in viewing these
alone, I cannot say that I am satisfied with the following arrangement. In drawing
it up I have paid due attention to the arrangements proposed by Tryon, Stoliczka,
Zittel, S. A. Miller and others, and sought to avoid what has seemed objectionable in
each. At best the result is premature, and in submitting it in the hope that it may
prove a little nearer the truth than their schemes, I beg that it may be considered
with lenity.

LAMELLIBRANCHIATA. 485

Classification of paleozoic Lamellibranchiata.]

CLASSIFICATION OF PALEOZOIC LAMELLIBRANCHIATA.

Subkingdom MOTmUSG A:
cass LAMELLIBRANCHIATA, Biainvite.
order ASTPHONIDA, wWooawara.
Mantle lobes separate, siphons wanting. Pallial line without sinus.
Suborder MONOMYARIA.
A single adductor muscle, the anterior one wanting.
Family PECTENIDA#, Lamarck.

GENERA: Aviculopecten, McCoy; Crenipecten, Hall; Euchondria, Meek; Lyriopecten, Halil; Pernopecten,
Winchell; Pterinopecten, Hall; Streblopteria, McCoy.

Suborder HETEROMY ARIA.
Anterior adductor muscle very small, the posterior one large.
Family AVICULIDAS, dOrbigny.
GENERA: Actinopteria, Hall; Bakevellia, King; Ectenodesma, Hall; Glyptodesma, Hall; Liopteria, Hall;
Leptodesma, Hall; Limoptera, Hall; Monoptera, Meek and Worthen; Monotis, Bronn;
? Paleopinna, Hall; Posidonomya, Bronn; Pseudomonotis, Beyrich; Pterinea, Goldfuss ( Ver-
tumia, Hall); Pteronitella, Billings; Pteronites, McCoy; ? Ptychopteria, Hall.
Family PINNIDA®, Gray.
GENERA: Aviculopinna, Meck; Pinna, Linne.

Family AMBONYCHIIDA#, Miller.

GENERA: Allonychia, Ulrich; Ambonychia, Hall (restricted); Amphicelia, Hall; Anomalodonta, Miller;

Anoptera, Ulrich; Byssonychia, Ulrich; Byssopteria, Hall; Clionychia, Ulrich ; Eetéfoptera,,.

Ulrich; Fridonychia, Ulrich; Mytilarea, Hall; Paleocardia, Hall; Plethomytilus, Hall.
Psilonychia, Ulrich.

Family CHASNOCARDIID AS, Miller.
GENERA: Chenocardia, Meek and Worthen; Megambonia, Hall.
Family MYTILIDA®S, Lamarck.

GENERA: ? Anthracomya, Salter; ? Anthracoptera, Salter; Gosselettia, Barrois; Lithodomus, Cuvier ( Litho-
phaga, Bolton); Modiella, Hall; Modiola, Lamarck ; Myalina, Koninck; Mytilops, Hall;
2 Spathella, Hall. ~

Family MODIOLOPSID/4, Ulrich.
UShilincr
GENERA: Actinomya, Ulrich; ? Aristerelld, Ulrich; Colpomya, Ulrich; ? Cymatonota, Ulrich; ? Cypricardella,
Hall; ? Endodesma, Ulrich ; Eurymya, Ulrich; Goniophora, Phillips; Modioledon, /Ulrich ;
Modiolopsis, Hall; Modiomorpha, Wall; Orthodesma, Hall and Whittield; ? Prolobella, Ulrich;
? Psiloconcha, Ulrich; ? Pyanomya, Miller.

ope

486 THE PALEONTOLOGY OF MINNESOTA.

(Classification of paleozoic Lamellibranchiata.
Family CYPRICARDINIID, (Provisional.)
GENUS: Cypricardinia, Hall.
Family CYRTODONTID A, Ulrich.

GENERA: ? Cypricardites, Conrad; Cyrtodonta, Billings; Ischyrodonta, Ulrich; Matheria, Billings; Orlonella,
Ulrich. ? Ptychodesma, Hall; Vanuxemia, billings; Whitella, Ulrich.

Suborder HOMOMY ARIA.

Mantle lobes either separate or united posteriorly. The two adductor muscles of nearly equal
strength.

Family ARCIDAS, Lamarck.

GENERA: Carbonarca, Meek and Worthen; Macrodon, Lycett; Nyassa, Hall; ? Spenotus, Hall.

Family PARARCIDA, (Provisional).
GENERA: Cardiola, Broderip; Cardiopsis, Meek and Worthen; Dewiobia, Winchell; Glyptocardia, Hall;
Lunulicardium, Minster; Orecardium, Herrick; Panenka, Barrande; Paracardium, Hall;
Pararca, Hall.
Family NUCULIDAS, Gray.
GENERA: ? Clidophorus, Hall; Ctenodonta, Salter (Tellinomya, Hall ); Goniodon, Herrick; Nucula, Lam-
arck; Nuculana, Link; Nuculites, Conrad; Palceoneilo, Hall; ? Pyrenomeeus, Hall; Yoldia,
Moller.
Family LYRODESMIDAS, Ulrich.
GENERA: Adodesma, Ulrich;—Ischyrina,Billings;—Lyrodesma, Conrad; Lechnophorus, Miller>
Bam, Seehnophortoar Wetlee
Family TRIGONIDA4, Lamarck.
GENERA: ? Cytherodon, Hall; ? Schizodus, King.

Family UNIONID AS
GENERA: ? Amnigenia, Hall; ? Anthracosia, King; Prisconaia, Conrad.
Family ELYMELLIDA), (Provisional).
GENERA: Elymella, Hall; Glossites, Hall.

Order SIPHONIDA, Woodward.

Mantle lobes more or less united; siphons of varying lengths, either separate or united, are
developed; both adductor muscles well developed.

Family SOLENOMYID/AS, Gray.
GENERA: Solenomya, Lamarck; Clinopistha, Meek and Worthen; Phthonia, Hall.

Family SANGUINOLITIDAS, Miller.

IENERA: Promacrus, Meek; Sanguinolites, McCoy.

LAMELLIBRANCHIATA. 487

Classification of paleozoic Lamellibranchiata.]
Family PHOLADELLIDA®, Miller.

GENERA: Allorisma, King; Chenomya, Meek and Worthen; Cimitaria, Hall; Pholadella, Hall; Physe-
tomya, Ulrich; Rhytimya, Ulrich.

Family GRAMMYSIID As, Hall.

GENERA: Cuneamya, Hall and Whitfield; Grammysia, De Verneuil; ? Leptodomus, McCoy; ? Sedgwickia,
McCoy; ? Sphenoliwm, Miller; Saffordia, Ulrich.

Family ASTARTIDA®. Gray.
GENUS: Astartella, Hall.
Family MEGALODONTIDA®. Zittel.
GENERA: Megalodon, Sowerby; Megalomus, Hall: ? Plethocardia, Ulrich.
Family LUCINIDA®, Deshayes.
GENUS: Paracyclas, Hall. .
Family CYCLOCONCHID%, (Provisional).
GENERA: Cycloconcha, Miller; ? Anodontopsis, McCoy. @+leeledsn ay Ulrich.
Family CONOCARDIID 4S, Miller.
GENERA: Conocardium, Brown: ? EFopteria, Billings: Euchasma, Billings.
Family CARDIOMORPHID AS, Miller.
GENERA: Cardiomorpha, Koninck; Edmondia, Koninck; Vuthydesma, Hall; Protomya, Hall.
Family SOLENIDAS, Adams.
GENUS: Solenopsis, McCoy; Palcosolen, Mall; ? Orthoncta, Conrad.
Family PALATANATINID/®, Miller.
GENERA: TIlionia, Billings; Palwanatina, Hall; Prorhynchus, Hall.

Family PROTHYRIDA®, Hall.

GrENus: Prothyris, Meek.

The literature pertaining to Lower Silurian Lamellibranchiata is not only
meager but, in great part, unreliable. The principal cause for the latter is to be
found in the want of experience of the authors, who, failing to understand the effects
of pressure to which a large proportion of the shells have been subjected, have thrown
together as identical widely different forms, and oftener, perhaps, distinguished the
distorted specimens from those which have more nearly retained the normal form.
The illustrations also are too often, if not entirely worthless, misleading. Here, more
than in any other part of the study, the greatest care and experience are required.
Entire and undistorted specimens are not by any means the rule, so that slight

488 THE PALEONTOLOGY OF MINNESOTA.

(Classification of paleozoic Lamellibranchiata.

restorations of the outline, if the figures are to be of real assistance in the identifi-
cation of the species, are generally not only desirable but necessary. An absolutely
correct reproduction of an imperfect specimen might be quite sufficient for the
trained specialist, but not for the beginner. He requires all we can give him, and I
know from experience that an approximation even to an “absolutely correct repro-
duction” is anything but common among illustrations of early Lamellibranchiata.

In the accompanying plates nearly all the specimens are represented as entire,
but in each instance the fact of the restoration is mentioned or indicated by a
fracture-like line. Respecting the drawings, I shall say only that they were in
every case made by myself and with as great care and fidelity to nature as I could
command.

The synonomy of the species is scarcely as complete as I could wish, but as the
volume must be kept within certain limits, and because it is in many instances at
least doubtful that current identifications of the old species are really the same as
the originals, I have restricted the synonomy to the citation of the first work con-
taining a description and such of subsequent memoirs as added materially to our
knowledge of the objects under consideration. Desiring also to save as much space
as possible for general remarks, I have generally avoided what seemed unnecessary
repetition by giving full descriptions of the principal species only. In characterizing
the others I have depended chiefly upon comparisons, which, if they are complete, I
hold to be more useful than bare descriptions.

While the greater part of the northwestern material used was collected by myself, and is now part
of my private cabinet, about one-fourth of the whole belongs to the survey museum, for which, as is shown
by the museum register, the specimens were collected chiefly by Prof. N. H. Winchell, Prof. C. L. Herrick,
and Messrs. W. H. Scofield and Charles Schuchert. For much of the remainder I am personally indebted
to Mr. Scofield, who, with unusual generosity, allowed me to select anything I desired from his extensive
private collection of Minnesota fossils. I am under obligations also to Dr. C. H. Robbins, of Wykoff, Min-
nesota, for several choice specimens from the Galena limestone of Fillmore county; likewise to Prof. C. W.
Hall, Mr. A. D. Meeds and Mr. A. H. Elftman for good specimens collected by them in the vicinity of
Minneapolis.

LAMELLIBRANCHIATA. . 489

Lamellibranchiata.]

Class LAMELLIBRANCHIATA.

( PELECYPODA.)
Family AMBONYCHIID, Miller.

Valves equal, very inequilateral; beaks prominent, terminal or nearly so; posterior
cardinal region more or less alate; anterior side abruptly convex, with or without a
byssal opening. Small cardinal and elongate posterior lateral teeth may be present
or wanting. Posterior adductor impression large, bilobed (the upper part probably
formed by a pedal muscle), situated above and behind the center of the valves.
Anterior adductor wanting or very small, situated in the umbonal region. Pallial
line simple, strongly impressed in the anterior region, becoming obsolete near the
anterior extremity of the hinge.

This family is unquestionably a valid one, and readily distinguished from the
Aviculide with which its old genera are usually associated. In that family of shells
the valves are always unequal and drawn out in front of the beaks into a distinct
wing or lobe. The Ambonychiida, on the contrary, are always equivalved and with-
out an anterior wing, the situation of the beaks being approximately terminal.

As may be seen from the scheme of classification on page 485, I have extended
the limits of the family so as to include several genera that are very differently
arranged by other authors. Thus Amphicelia, Hall, is regarded as the type of a new
family by Miller, while Whitfield has said that the genus is probably identical with
Leptodomus, McCoy, and Meek and Worthen placed it near Pterinea. But, as I shall
show in another work, Amphicwlia possesses every essential character of the present
family. Palwocardia, likewise founded by Hall upon a Niagara species, also is closely
related to Ambonychia. Hall’s Mytilarca and Plethomytilus again, can be shown, I
believe, to be direct descendants of Lower Silurian types of this family and should
not be placed with the Mytilide.

Genus AMBONYCHIA, Hall (emend. Ulrich).

Ambonychia (part.), HALL. 1847. Pal. N. Y., vol. i, p. 163. Not Ambonychia, Hali, 1859, Pal. N.
Y., vol, iii, pp. 269 and 523; nor of American and European authors
generally.

Equivalved and profoundly inequilateral shells; valves ventricose, very thin,
closing tightly all around; beaks full, strongly incurved. Surface with fine radiating
strive, crossed by concentric growth lines and obscure undulations. Internally a thin
plate passes vertically down from the anterior end of the hinge plate separating a

490, THE PALEONTOLOGY OF MINNESOTA.

(Lamellibranechiata.

small lobe, immediately beneath and sometimes a little in front of the beaks, from the
umbonal cavity. Hinge plate narrow, with a few ligament striations and two small
oblique cardinal teeth; no lateral teeth. Muscular impressions and pallial line very
faint.

Type: A. bellistriata Hall.

It will be seen that the foregoing description of this genus is, in many respects,
widely different from that adopted by all preceding authors. Hall’s original diag-
nosis is, of course, too broad and on the whole indefinite, since it included species
which subsequent study proved to be quite different from the typical species. Again,
the commonly accepted characterization of Ambonychia, since the publication of
Hall’s notes on the genus in 1859, is based upon his A. radiata and not upon A. belli-
striata, which, of all the species placed under Ambonychia by him in 1847, alone is
entitled to the distinction of being the type. Ambonychia, therefore, as generally
understood, is synonymous with the group of shells which now propose to name
Byssonychia, and quite distinet from Ambonychia as based upon A. bellistriata and A.
orbicularis (Emmons), the two species first following the original description of the
genus.

This new interpretation of the genus may produce some confusion, but it is
necessitated by the rule of priority, which demands that when no type is mentioned
the first species to follow the original description must be regarded as the type of
the genus. _ Having then no alternative but to accept A. bellistriata as the type, I
have redefined the genus in accordance with the characters presented by that species
and four others, A. orbicularis Emmons, A. planistriata Hall, A. affinis, n. sp. and A.
amygdalina Hall, all of which, with the possible exception of the last, are unques-
tionably congeneric.

Compared with other members of the family, Ambonychia, as here understood,
differs from Clionychia, Ulrich, in having a small lobe-like cavity beneath the beaks
where, in that genus, there is a mere thickening of the margin of the valves. In
casts of the interior the whole upper part of the anterior side of Clionychia is
impressed to the edge of the valves, while in Ambonychia the same part presents a
small protruding, vertically elongate lobe, separated from the anterior side of the
rostral cavity by a sharply-impressed thin line. This lobe reminds one greatly of
the anterior adductor impression of Vanuxemia, but I could not satisfy myself that
it really lodged such a muscle. Other differences are that in Ambonychia the valves
are more ventricose and the umbones and beaks more strongly incurved, while the
surface is marked not only concentrically but also radially. In Byssonychia there is
a byssal opening in the anterior side and the hinge is strengthened by two or three
slender posterior lateral teeth. The Upper Silurian genus, Amphicelia, Hall, may

LAMELLIBRANCHIATA. 49]

Ambonychia planistriata.]

be more nearly related to Ambonychia than either of the genera mentioned. Certain
it is that I find it more difficult to point out the distinguishing features than | did
in those cases. The general appearance of the shells of the two genera-(Ambonychia
and Amphicwlia) is very similar, both in the matter of form and in their surface mark-
ings. The hinge also is very much the same in the two genera, the chief difference
being that the area is wider in Amphicwlia. The greatest difference, however, seems
to lie in the antero-cardinal region, where the margin of the latter is thickened,

causing casts of the interior to appear as broadly impressed in this region.

AMBONYCHIA PLANISTRIATA Jal.
PLATI2 XXXV. FIGS. 3 and 4.

Ambonychia planistriata MALL, 1861. Rep’t. Sup’t. Geol. Sur. Wis., p. 32.

Shell obliquely acuminate-ovate or subrhomboidal, ventricose, with the point of
greatest convexity near the center of the antero-cardinal half. Upper half of anterior
side somewhat flattened, nearly straight, sloping backward slightly, and more rapidly
below, into the basal margin, which, with the greater part of the posterior edge,
forms a semicircle; postero-cardinal margin subangular, hinge line straight, one-
third or a little less shorter than the greatest length of the shell beneath, Beaks
prominent, strongly incurved; umbones full and rounded; posterior cardinal slope
concave. Surface marked by distinct, broad and shallow concentric undulations
and fine radiating striz, of which about twelve occur in 5 mm. at the margin of an
average example. These striw, which are flattened and separated by very narrow
interspaces, are cancellated by another set of even finer concentric lines. ‘Test very
thin, hinge plate narrow, apparently with two cardinal teeth in each valve and no
lateral teeth. In good casts of the interior the antero-cardinal lobe is sharply
defined.

This rare and beautiful species is readily distinguished from A. bellistriata Hall,
and A. orbicularis Emmons, sp., by. its concentrically undulated surface. In this
feature it is like Clionychia undata Emmons, sp., but that form, aside from the fact
that it has the characters of Clionychia, is less ventricose, of somewhat different
shape and without radiating lines. For comparisons with A. afinis Ulrich, see that
species.

Formation and locality.—From the ‘‘ Lower Blue limestone” at Mineral Point and Beloit, Wiscon-
sin, and the equivalent limestones at Cannon Falls, Minnesota, and Lee county, Lilinois.

Mus Reg. No. 8327.

492 THE PALEONTOLOGY OF MINNESOTA.

[Ambonychia bellistriata.

AMBONYCHIA BELLISTRIATA /Hall.
5 PLATE XXXY, FIGS. 1 and 2.

Ambonychia bellistriata HALL, 1847. Pal. N. Y., vol. i, p. 163. Not Ambonychia bellistriata 8. A.
Miller, 1874, Cin. Quart. Jour. Sci., vol. i, p. 14.

The Minnesota specimen illustrated on the accompanying plates differs slightly
in its outline from the original figures of the species given by Hall im the work
cited.* The hinge line is a trifle longer and the anterior side less uniformly curved.
Still, I cannot for a moment doubt its specific identity with the types of the species,
since it possesses all the more essential characters. The beaks and umbones are
very prominent and strongly incurved, and the radiating striz fine (about twelve or
thirteen in 5 mm.) and apparently of the same character as in A. planistriata, except-
ing that they show no traces of the fine concentric lines noticed in that species.

Compared with A. planistriata the present species is found to differ in the relative
narrowness and greater prominence of its umbones, and in wanting the shallow con-
centric undulations, which are always a striking feature of that species. A. orbicu-
laris is a more erect and rounded form, and not so ventricose.

The name Ambonychia bellistriata occurs in all the published catalogues of the
fossils of the Cincinnati group, but the species referred to in the lists is really a very
different one. Indeed, it is a true member of the proposed genus Byssonychia, and
closely related to the type of that genus, B. radiata Hall, sp.

Formation and locality.—In the central part of the Trenton limestone at Middleville and Trenton
Falls, New York; and in the middle Galena near Wykoff, Minnesota.

AMBONYCHIA AFFINIS, 2. SD.

PLATE XXXV, FIGS. 5—%.

This species or variety is most probably a later phase of A. planistriata Hall,
and as it resembles that species very greatly it will be sufficiently characterized by
pointing out the differences. Thus, the beaks and umbones are a little less tumid
and the convexity of the shell correspondingly less. The shell is also a trifle more
erect and rounder, the hinge line slightly shorter and the postero-cardinal margin
more rounded. Finally, the concentric undulations are much more obscure, while
the radiating striae are coarser, there being only eight in 5 mm. to twelve in the
same space for that species. At first I thought the species might prove the same as
A. orbicularis Emmons, sp., but a comparison with Hall’s figures in vol. i of the Palz-
ontology of New York, will show that the anterior side of the New York species is

*An examination of the types of the species, which are now preserved in the American Museum of New York City,
proves that figs. 4a and 4b (on plate 36) are faulty in showing the radiating lines stronger than natural. Indeed, they
ure quite as strong in these figures as in the magnified views of the surface represented in fig. 4d.

LAMELLIBRANCHIATA. 493
Ambonychia affinis.]

more prominent, giving it a more erect appearance than any of the other species
referred to the genus. Nor can I find that A. orbicularis ever has concentric undu-
ations.

Formation and locality—Middle Galena, Weisbach’s dam, near Spring Valley, Minnesota; also in
Carroll county, Llinois.

Mus. Reg. No. 83438.

AMBONYCHIA AMYGDALINA J/all.
PLATE XXXV, FIGS. 8 and 9.

Ambonychia amygdalina HAL, 1847. Pal. N. Y., vol. i, p. 165.

None of the specimens seen by me preserve the surface characters well enough
to prove that this species was provided with radiating lines. Obscure traces of such
strive are to be made out on one of the casts of the interior, but the evidence is not
sufficient for me to assert that they are what they seem. Still, it is highly probable
that radiating striz will be found on perfect specimens, in which case the species
would stand very near A. bellistriata, differing from it, so far as we can now see,
chiefly in its greater size, less incurved beaks, flatter anterior side and less angular
postero-cardinal margin.

The anterior lobe is longer, more sunken and less sharply defined in this species
than in the others here referred to Ambonychia.

Formation and locality.—Middle Galena of Goodhue county, Minnesota. The New York type of
the species is credited to the Trenton limestone at Adams, Jefferson county. Billings also catalogues
the species from the same horizon in Canada.

Genus CLIONYCHIA, Ulrich.

Ambonychia (part.) HALL, 1847. Pal. N. Y., vol. i, p. 163.
Clionychia, Ubnicu, 1892. American Geologist, vol. x, p. 97; Clionychia, MILLER, 1892. First Ap-
pendix, N. A. Geol. and Pal., p. 699.

Shells equivalve, moderately covvex, subalate posteriorly; beaks terminal, com-
paratively small, not very prominent and but little incurved. Cardinal line straight,
rather long, forming an angle of less than 90° with the anterior side. Surface marked
concentrically only. No byssal opening, the margins closing tightly all around.
Muscular impressions situated in the postero-cardinal third, large, bilobed, the
lower lobe much larger than the upper. Pallial line simple, extending from the
posterior adductor to the rostral cavity. Hinge plate of moderate strength, without
cardinal or lateral teeth, excavated longitudinally for a linear ligament. Upper
part of anterior edge thickened, producing a more or less well-marked impression
in this part of casts of the interior. Anterior pedal muscle attached a short distance
behind the beaks.

Type: Ambonychia lamellosa Hall.

494 THE PALEONTOLOGY OF MINNESOTA.

[Ambonychia amygdalina.

This well marked genus embraces probably the simplest and earliest types of
the family, from which all the other genera descended. Yet, while a direct line to
Mytilarca and Plethomytilus seems obvious enough, I must confess my inability to
bridge over the gap between the radially ribbed genera on the one hand—and these
form a very natural and closely interrelated group—and those in which the surface
is marked with concentric lines only, on the other. At present, therefore, the evi-
dence favors the conclusion that in times preceding the Chazy there existed a more
primitive type still that combined the characters of the two groups.

Compared with Ambonychia, as here restricted, the present genus differs in its
smaller umbones and less incurved beaks, in wanting radiating strive and in the
structure of the anterior side, there being, instead of a clavicle-like plate or ridge
‘beneath the beaks, a mere thickening of the margin, leaving a cavity or impression
in the cast where that genus presents a small lobe. Mytilarca, Hall, which probably
was not evolved till after the close of the Lower Silurian, is distinguished by its
cardinal and posterior lateral teeth, and more oblique form.

In the remarks following the original description of the genus I mentioned
Ambonychia amygdalina Hall, as belonging here. This I now believe to have been
an error. Respecting A. nitida and superba, described by Billings from Anticosti,
and other concentrically marked species that have been referred to Ambonychia, it
may suffice to say that they are not congeneric with the types of that genus. Their
true relations cannot be established until we know something definite about their
hinges. Some of the species in question are much like 4. acutirostra and aphiea, two
species described by Hall from the Niagara rocks of Wisconsin and Illinois that

should go with Mytilarca and not with Clionychia.

CLIONYCHIA LAMELLOSA all.
PLATE XXXV, FIGS. 10-14.
Ambonychia lamellosa HALL, 1861. Rept. Sup’t. Geol. Sur. Wis., p. 31; WHITFIELD, 1882, Geol.
Rep. Wis., vol. iv, p. 205.

Ambonychia attenuata HALL, 1861. Rep. Sup’t. Geol. Sur. Wis., p. 38; WHITFIELD, 1882, Geol.
Rep, Wis., vol. iv, p. 206.

Shell obliquely, subquadrangular or subovate in outline; binge line straight,
generally but little shorter than the length of the shell beneath; anterior margin
nearly straight, sloping backward five to fifteen degrees from a vertical line, below
curving rather rapidly into the strongly convex basal line; posterior margin more
gently curved, joining the hinge line sometimes sharply at other times gradually.
Valves rather strongly convex, most ventricose in the umbonal region and near the
anterior side where the slope to the edge is abrupt; cardinal slope gentle, in some
cases nearly flat, in others distinctly concave. Beaks terminal, small, acutely

LAMELLIBRANCHIATA, 495

Clionychia nitida.]

attenuate in casts, generally curving slightly forward, projecting but little above
the hinge and scarcely incurved. Beneath them the anterior side of casts presents
a broad and often sharply-defined depression which, in extending downward, gradu-
ally dies out at or a little beneath a point midway between the base and the hinge.
Surface, especially near the free margins, marked with numerous, unequally dis-
tributed concentric lines of growth, having the appearance, even on the casts, of
being the edges of overlapping lamellae. Hinge plate rather strong, without teeth,
the ligamental area wide and faintly striated. Muscular scar bilobed, situated almost
entirely within the postero-cardinal third of the valve. Pallial line simple, extend-
ing up the anterior side apparently to the cavity of the beak.

The form of this species seems to be quite variable, but after a careful study of
humerous specimens I have concluded that much of this supposed instability is due
to distortion through pressure. On the other hand, for the same reason, | found it
utterly inpossible to detect really normal specific differences between the specimens
which Hall in his original work and Whitfield in the later volume cited above have
separated as two species under the names Ambonychia lamellosa and A. attenuata.
According to my view the latter is founded upon specimens of the former whose
original form was changed by pressure acting so as to decrease the diagonal or the
vertical diameter of the valves, causing them to appear abnormally elongate.
Whitfield’s figure of A. attenuata, (op. cit. plate V, fig. 6) represents, instead of the
left, most surely the right side of an obviously distorted specimen. It is a little
surprising that a paleontologist of such wide experience as Prof. Whitfield should
have failed to observe the evidences of distortion, and more so still, that he should
mistake one valve for the other, especially of a specimen that preserves the posterior -
adductor sears. These we know are situated in the postero-cardinal third of the
valves, but his error leads him so far astray that he asserts without qualification
“they are situated near the anterior border of the valve.”

This species cannot be confounded with the associated Ambonychia planistriata
Hall, but care is required in separating it from the two species of Clionychia next
described.

Formation and locality.—Lower Blue and Upper Buff limestones, Beloit, Mineral Point and Janes-
ville, Wisconsin; Dixon, Illinois, and the upper part of the Trenton limestone at Minneapolis and St.
Paul, Minnesota.

Mus. Reg, Nos. 5676, 8314.
CLIONYCHIA NITIDA, 2. Sp.
PLATE XXXV, FIGS. 15 and 16.

This form is so much like the preceding (C. lamellosa) that it scarcely deserves
specific recognition. Critically compared it is found to differ in the following

496 THE PALEONTOLOGY OF MINNESOTA.

[Clionychia erecta—rhomboidea.

respects: The umbonal slope is less defined, the whole surface being more uni-
formly convex, the beaks not so attenuate and more incurved, and the concentric
growth lines not nearly so sharp, much more numerous and more equal. Casts of
the interior are almost smooth, and the shell substance must have been very thin.
The anterior side also is less concave, the shell smaller and the valves proportionally
a little more convex.

Formation and locality.—Central part of the Trenton limestone at Minneapolis, Minnesota.

Mus, Reg. No. 5099.
CiionycHiA ERECTA Hall.
PLATE XXXV, FIGS. 17 and 18.
Ambonychia erecta HALL, 1861. Rep. Sup’t. Geol. Sur. Wis., p 32.

This species also is exceedingly like C. lamellosa, and for a time I was inclined
to question the propriety of maintaining it. A more careful comparison, however,
has revealed slight peculiarities that cause me now to view the separation with some
favor. The valves of C. erecta are not so convex and more nearly square, the outer
side being almost vertical and more produced below, the posterior side is straighter
above and the postero-cardinal angle sharper. In all other respects the two forms
are, so far as we can learn, identical. C. nitida is more oblique, its valves more
convex and their surface markings finer.

Formation and locality.—Trenton limestone Beloit, Wisconsin, and Minneapolis, Minnesota.

CLIONYCHIA RHOMBOIDEA Ulrich.
PLATE XXXV, FIGS. 19 and 20.

Clionychia rhomboidea ULRICH, 1892. Amer. Geol., vol. x, p. 97.

Shell, as seen in casts of the interior, of medium size, very oblique, rhomboidal
in outline, the anterior and posterior and the dorsal and ventral margins subparallel.
Dorsal edge nearly straight, likewise the posterior, the two lines meeting at an angle
of about 120°. Postero-ventral margin sharply curved, the ventral side gently convex
and rounding almost uniformly up to the base of the anterior side, from which point
the outline continues to the beaks in very nearly a straight line. Beaks terminal,
small, pointed, projecting slightly above the hinge line, scarcely incurved. Umbonal
ridge strongly convex, extending toward the postero-ventral extremity in a slightly
curved direction, so that the slopes on the anterior and ventral sides are more abrupt
than on the opposite sides. Point of greatest convexity a little in front of and above
the middle.

Interior with hinge plate rather wide and strong, and the anterior edges of the
valves, for a short distance beneath the beaks, much thickened inwardly, the decay

LAMELLIBRANCHIATA. 497

Clionychia undata.

of the shell leaving a distinct depression in the casts. Muscular scars large, situated
about midway in the postero-car linal half of the valve, the two lobes united by a
narrow neck, the upper one oval in shape and about one-third as large as the more
nearly circular lower one. }

The posterior extremity is more produced and more narrowly curved than in the
other species referred to this genus.

Formation and locality.—Lower limestone of the Trenton formation at Minneapolis, Minnesota.
Mus. Reg. No. 5526.

CLIONYCHIA UNDATA [/mmons.
PLATE XxXxXV. FIGS. 21 and 22.

Plerinea undata EMMONS, 1842. Geol, Report. New York, p. 395,
Ambonychia undata HALL, 1847. Pal. New York, vol. i, p. 165.

Shell subquadrate, cardinal margin long, straight, anterior side straight, nearly
vertical, curving sharply backward below into the gently convex base, which in its
turn curves rapidly upward into the broadly rounded posterior margin; antero-
cardinal angle about 85°, postero-cardinal angle about 115°. Beaks prominent,
attenuate, slightly incurved, with the umbones strongly convex, the anterior slope
very abrupt, the rapidity of the descent becoming gradually less in following the
margin around to the posterior extremity of the hinge, where it is very gentle;
cardinal slope concave, becoming strongly so and very abrupt in nearing the beaks.
Surface marked with broad concentric folds, which are strongest on the cardinal
and umbonal slopes and fade away gradually in curving around to the anterior side.
Immediately beneath the beaks the anterior side of a good cast of the interior
presents a sharply defined lunule-like impression, which, having been occupied by
an internal thickening of the margin of the valves, was scarcely indicated on the
exterior of the shell. Hinge plate narrow, muscular impressions undetermined.

The above description is based upon the specimen illustrated on plate xxxvy.
It presents no evidence of distortion and seems to be in every respect in a good
state of preservation. Comparing this example with Hall’s description and figures
of the New York types of the species we observe that it differs in several particulars
that might be regarded as important. The outline is more nearly quadrate, and the
convexity of the valves less, giving a form that deviates from the figures of the
New York specimen precisely as C. erecta does from C. lamellosa, Hall also mentions
the absence of a “definite lunette,” while such an impression is distinctly present
in the casts of the Minnesota specimens. Despite these differences | am almost
contident of the specific identity of the latter and the types of the species, because |

am inclined to doubt the actual existence of the discrepancies noticed.

32—

495 THE PALEONTOLOGY OF MINNESOTA.
{[Byssonychia.

The broad undulations of the surface distinguish the species from the other

a

shells referred to Clionychia.

Formation and locality.—Middle Galena, Fillmore and Goodhue counties, Minnesota; associated
with Zygospira uphami W. and §., Vanuxemia abrupta Ulrich and Lichas (Hoplolichas) robbinsi Ulrich.
The original specimen is from the Trenton limestone at Watertown, New York.

Genus BYSSONYCHIA, n. gen.

Ambony chia (part.), HALL, 1847. Pal. New York, vol. i, p. 163.

Ambonychia, HALL, 1859. Pal. New York, vol. iii, pp. 269 and 5233 also of all American and
European authors who have described that genus subsequent to
this date.

General aspect as in Ambonychia, Hall, excepting that the beaks and umbones
are not so full. A well-defined byssal opening in the upper half of the anterior side.
Hinge with a striated ligamental area, several small cardinal teeth and generally
two or three slender lateral teeth near the posterior extremity. Posterior adductor
impressions large, situated a little behind the center of the valves. Pallial line
simple, terminating in the rostral cavity.

Type: Ambonychia radiata Hall. (See fig. 35, v1, p. 477.)

The erection of this genus became a necessity when a critical study of Ambony-
chia bellistriata Hall, and several other species undoubtedly congeneric with that
peculiar type of the genus Ambonychia, proved them to be without not only lateral
teeth but a byssal opening as well. On the other hand byssonychia has nothing like
the anterior subrostral clavicle, while the external radiating coste are nearly always
stronger than ‘in Ambonychia. We have, therefore. at least three ordinarily valid
generic differences to separate the two genera. Indeed, there is room for one or
more intermediate genera. Two very nearly such groups actually exist in the Cin-
cinnati rocks and I hope to publish descriptions of them in the next (7th) report of
the state geologist of Ohio. One (Allonychia) will contain, besides the type, Ambony-
chia (Megambonia) jamesi Meek, two new species. They are all more erect shells,
possessing a protruding byssal opening, a short hinge with wide ligamental area,
but neither cardinal nor lateral teeth. The other group (H7ridonychia) is based upon
several elongate new species, having but little incurved beaks, scarcely ventricose
umbones, a long and narrow byssal opening, thin hinge plate and no teeth.

Byssonychia is closely related to Anomalodonta, Miller, but is distinguished by its
hinge, that genus having neither truelateral nor cardinal teeth. Itis to be admitted,
however, that in certain species, otherwise precisely like Byssonychia, the posterior
lateral teeth are nearly or quite obsolete. Descriptions of these and other new

species of this genus have been written for the Ohio work above mentioned.

LAMELLIBRANCHIATA. 499

BySsonychia intermedia.]

The Ambonychia intermedia Meek and Worthen, of the Galena, seems to be the
earliest species of Byssonychia now known. Perhaps contemporaneous with this is a
form, occurring in the Trenton of Kentucky and Tennessee, that is scarcely distin-
guishable from the Hudson River B. radiata. Nine or ten additional species, of
which two only are described (A. retrorsa and robusta, of Miller) occur in the Hudson
River and Cincinnati rocks. So far as known the genus became extinct with the

close of the Lower Silurian.

ByssonycHta INTERMEDIA Meek and Worthen.
PLATE XXXV, FIGS. 23-26.
Ambonychia intermedia MEEK and WortTHEN, 1868. Geol. Sur. IIl., vol. iii, p. 306.

Shell small, rhombic-subovate, the length and hight about as eleven is to fourteen;
gibbous in the umbonal, anterior and central regions, compressed and subalate postero-
dorsally. Hinge line a little shorter than the greatest antero-posterior diameter of
the valves, ranging at an angle of about 90° with the anterior margin. Anterior side
truncated nearly vertically above, below rounding backward into the base, the outline
around the lower two-fifths of the shell forming nearly a regular semicircle. Poste-
rior margin straightened above or rounding regularly into the hinge line. Beaks
prominent, full, obtusely pointed, strongly incurved with a slight forward direction.
Internal casts are somwhat excavated in the upper part of the front in the space
surrounding the small byssal opening, and between the latter and the points of the
beaks there is a small protuberance representing the filling of a little cavity at the
extremity of the hinge plate. Surface marked by rather fine radiating plications,
the total number, as near as can be determined from casts, being between forty-five
and fifty. ‘They are coarser on the ventral slope than on the posterior wing, always
simple and increase in strength with the growth of the shell. On large casts the
coste are not defiued except at the free margins, the rest of the surface being smooth.

Muscular sear and pallial line unusually obscure, their positions and form not
certainly determined, :

This little shell is a true Byssonychia and quite different from Ambonychia belli-
striata Hall, with which Meek and Worthen compare it. It is related to the follow-
ing species, but a nearer ally is found in the B. vera Ulrich, of the lower part of the
Cincinnati exposures. That species, of which an excellent internal cast is figured on
page 479 (fig, 36, pl. V), is less gibbous, more oblique and has smaller beaks, while
the muscular scars and pallial] line are usually more distinctly impressed.

Formation and locality.—Galena limestone, Mount Carroll, Illinois; Oshkosh, Wisconsin, and near

Wykotf, Minnesota.
Mus. Reg. No. 8359.

500 THE PALEONTOLOGY OF MINNESOTA.

. Pa
[Byssonychia tenuistriata .

ByssoNnYCHIA TENUISTRIATA, #1. Sp.

Vig. 39. Byssonychia tenwistriata, n. sp. Hudson River group, Granger, Minnesota. The right side
and a front view of an imperfect cast of the the interior. Mus. Reg. No. 8371.

Shell rather small, subovate, moderately ventricose in the umbonal region and
anterior half, compressed in the postero-cardinal region where the surface is dis-
tinctly concave; anterior slope strongly convex, but scarcely abrupt; beaks small,
projecting but little, moderately inecurved. Hinge line comparatively short, the
outline passing rather gently into the broadly-rounded posterior margin; basal line
strongly convex, curving uniformly into the ends; anterior side slightly concave
above, neatly convex below. Byssal opening small, its position high, it and the
surface around it appearing in casts as a distinct impression immediately beneath
the beaks. Surface marked with very fine radiating strie and obscure concentric
varices of growtb, both showing through the marginal parts of the shell, so as to be
visible on good casts of the interior. The total number of the radiating striz is
probably more than seventy. Near the base of the specimen figured eleven were
counted in the space of 5 mm.

This species is closely related to B. vera Ulrich, (see ante p. 479, fig. 36, V)
from the Utica horizon of the Cincinnati group of Ohio, differing from it chiefly in
its finer radiating strize and more impressed byssal opening. B. intermedia M. and

W., of the Galena, has coarser strive and is a more ventricose shell.

Formation and locality.—Rare in the upper part of the Hudson River rocks at Granger and Spring
Valley, Minnesota, and in an equivalent position at Richmond, Indiana.

Mus. Reg. Nos. 8370, 8371.

Family MODIOLOPSIDAj, n. fam.

Shell equivalved, usually elongate ovate, but varying to oblong subquadrate,
generally thin; valves fitting closely or gaping slightly at one or both ends. Beaks
near the anterior end, but never terminal. Hinge long, of variable strength, edentu-
lous or with one or two cardinal teeth in one or both valves. Ligament long, linear,
external and internal. Anterior adductor impressions rather large and distinct,

situated between the beaks and the anterior extremity; above them a very small

LAMELLIBRANCHIATA. 501
Modilolopside.]

pedal muscle scar. Posterior adductors large, very faintly impressed, situated Jess
than their diameter from the posterior extremity of the hinge. Pallial line simple.
Inner side of valves usually with one or two obtuse ridge-like thickenings extending
from the beaks obliquely backward toward the center of the ventral margin.

Of the various genera included in this family in the scheme of classification on
page 455, [am satisfied that some of those preceded by a question mark will be sooner
or later placed elsewhere. No more satisfactory arrangement having suggested itself,
they were referred here, because their known characters agree with one or another
of the more typical genera. Thus, Aristerella, aside from its unequal valves,
compares favorably with Hurymya, Cypricardella seems to be related to Modio-
morpha, and Endodesma to Modiolopsis and Cymatonota, while Psiloconcha, in a general
way, resembles Aetinomya. ‘But of Pyanomya too little is known to venture an
opinion as to its ultimate placement, the only excuse for recognizing the genus in
this connection being that it would be even more out of place in any of the other
families. The position of Prolobella also is quite uncertain.

Some of the species of Modiolopsis remind us so strongly of Modiola and Myoconcha
that we can scarcely escape the conviction that the latter genera, which are placed
respectively in the families Mytilide and Prasinidw by Stoliczka and Zittel, have
really descended from Modiolopsis. Still, | am of the opinion that the paleozoic
types constitute a more natural grouping by themselves than can be attained by
any of the courses adopted heretofore. . The position usually assigned to Modiolopsis
is near Modiola in the family Mytilidw, but Stoliczka and Zittel see greater resem-
blances with Myoconcha and therefore regard the genus as an early type of the
Prasinide. But both of these families, the first in partiular, seem to me to include
heterogeneous material, and if they were revised according to the genesis of the
Lamellibranchiata, I have no doubt their limits would be greatly modified.

The first reason to influence me for the separation of Modiolopsis from the
Mytilide occurred during a comparison with Myalina, Koninck, a genus that, while
it seems to be very justly associated with Mytilus, has no relation to Modiolopsis.
Indeed, according to my view, the progenitors of Myalina are to be sought for
among the Ambonychiide.

Next, a comparison with recent species of Modiola proved that while a general
resemblance obtained there were still certain features in which the genera here
classed as the Modiolopside agreed thoroughly among themselves and differed from
Modiola. Thus, in the latter, and the same is true of all the Mytilide, the anterior
adductor impression is always smaller and the posterior one situated farther from
the cardinal margin as well as of a shape, including the prolongation formed by the

pedal muscles, never seen in the paleozoic shells under consideration. On the whole

502 THE PALEONTOLOGY OF MINNESOTA.

LModiolopsis.

the configuration of these parts in the latter is much more like what we see in the
Cyytodontide. Another feature in which the Modiolopside resemble the Cyrtodontide,
and one that, so far as | am aware, has never been noticed in Modiola nor Mytilus,
is the presence on the inner surface, at any rate of all the thick shells, of one or two
obtuse ridges extending from the beaks obliquely backward-and toward the ventral
margin, producing corresponding more or less well-marked furrows on casts of the
interior. :

Finally, there is to be urged that it is only a few shells, like Modiolopsis modio-
laris and M. concentrica, in which the anterior end is narrow and unusually short,
and a byssal sinus present, that exhibit any striking resemblances to either Modiola
or Myoconcha. No one would, I believe, say this of elongate shells like M. arguta and
M. angustata, and when it comes to Orthodesma, which can ‘be shown to have origin-
ated in the same stock that produced Modiolopsis, all agree in removing that genus
far from the Mytilide.

The many points of agreement that may be noticed between the Modiolopside
and the Cyrtodontidew probably indicate a close union of the two groups in times
preceding the Chazy; but, as far back as our knowledge now extends, there prevailed
at least one important distinguishing feature. Namely, there existed a difference in
the shell structure which, though its exact nature is unknown, is nevertheless clearly
evidenced by the appearance of the two groups of fossils when they are preserved in
soft shales, the shells of the former always being covered by a black or dark film
never seen on the latter.

Genus MODIOLOPSIS, Hall.
Modiolopsis (part.), HALL, 1847. Pal. New York, vol. i, p. 157.

Shell more or less elongate, usually subovate, widest posteriorly; valves moder-
ately ventricose, closing tightly all around. Beaks small, near the anterior extremity;
umbones depressed by a flattening or depression which crosses the valves obliquely
and widening causes a straightening or sinuation of the basal outline. Hinge of
moderate strength, rarely straight, generally somewhat arcuate, without well-marked
teeth; an obscure oblique thickening beneath the beak of one valve and a corres-
ponding depression in the other occasionally distinguishable. Ligaments linear, °
external and internal, chiefly the former. Anterior adductor impression subovate,
large, deep, sharply defined on the inner side, occupying the greater part of the small
anterior end. Posterior scar very faintly impressed, large, subcircular, situated near
the center of the posterior third of the cardinal slope. Pallial line simple. Anterior
pedal muscle forming a minute pit in the under side of the hinge plate beneath the
beak. Posterior pedal muscles large, attached just above and in front of the adductor.

LAMELLIBRANCHIIATA. 503
Modiolopsis.]

Type: M. modiolaris Conrad, sp.

As here restricted and defined, this genus constitutes a well-marked group of
lower paleozoic shells. The oldest species, so far as known, occur in the Birdseye
and Black River divisions of the Trenton formation. Some of these are of an oval
type that, by gradual modifications of the base, evolved species of the MZ. modiolaris
type. At the same time there existed elongate forms like M. arguta, having so much
in common with Orthodesma that we cannot doubt that they indicate the primitive
stock from which Modiolopsis and Orthodesma were evolved. The M. arguta line
continued and formed a reasonably complete chain through WW. nana, M. mytiloides
Hall, M. angustata, and one or two undescribed species of the middle beds of the
Cincinnati group, into M. concentrica H. and W., a common species of the upper part
of that series of rocks in Ohio and Indiana, and into MW. excellens from equivalent
strata in Minnesota. In this case the form was shortened, the anterior end particu-
larly. In the M. modiolaris line, however, the changes were different. Here we may
begin with M. similis, an oval form with the posterior end broadly rounded and widest.
This seems to have gone over into an upper Trenton species (M. subrecta Ulrich, Ms.)
having a much narrower posterior end—indeed, the back and base are nearly parallel.
We next follow the type by easy stages through varieties occurring in the Utica
horizon to the normal form of M. modiolaris. Much indeed might be said upon these
not only interesting but important questions of evolution, and nothing would please
me more than to be allowed to demonstrate the positions here outlined. But time
and space are lacking, and the few points made are offered chiefly in the hope that
the suggestions may stimulate students to researches in similar lines. The field is
inviting and the results to be obtained all important.

The relations of the genus to the other genera of the family treated of in this
chapter will be discussed in the remarks following their descriptions.

No comparison of Modiolopsis and Modiomorpha, Hall, has, so far as I can learn,
ever been published. This is strange, since the species of the two genera are strik-
ingly similar. As a rule it seems they are regarded as differing widely, but in what
respects we are not informed. Mr. S. A. Miller, for instance, places them into two
distinct families, but fails to state his grounds for the separation.* A mistaken idea
seems to prevail—where it originated I cannot say—that the hinge of Modiolopsis
has lateral teeth, and this is given as the principal difference between the two genera
by Nettleroth.+

Now, let us see what differences really exist between them. Taking Modiomorpha
concentrica as representative of the Devonian genus, we find that, so far as external
characters are concerned, it would pass very well for a species of Modiolopsis. Even

*North American Geology and Valwontology, p. 458; 1889.
+Kentucky Fossil Shells, p. 216; 1889.

504 THE PALEONTOLOGY OF MINNESOTA.

[Modiolopsis similis.

its interior, in a casual glance, would pass, there being the same large and deeply-
impressed anterior adductor scar, and nearly every feature with which those conver-
sant with species of Modiolopsis are familiar. The exception is in the hinge, which
is found to have a slightly oblique fold or tooth over the muscular scar in the left
valve and a corresponding groove in the right. In true Modiolopsis this tooth is
wanting, or rather, it is but little developed, since an obscure thickening of the hinge
plate between the muscular impression and the beak is noticeable in many species
of Modiolopsis. Another feature is observed in Modiomorpha concentrica that may be
of importance. Namely, the hinge plates posterior to the beaks are wider than in
any Modiolopsis known. They extend inwardly and at the same time diverge, probably
for the reception of a strong internal ligament, the removal of the thin plate leaving
a sharp slit a little within the cardinal edge of casts of the interior. The value
of the character is to be tested only by its persistence in other species referred to
Modiomorpha. It is a matter worthy of being looked into, for it must be admitted
that another difference between Modiolopsis and Modiomorpha, besides the only one
now recognizable, is, to say the least, desirable. :

Of the numerous species which have been placed in this genus many proved
distinct when subjected to critical study. Others look doubtful, but must remain
here for want of material to determine their relations. Of those to be removed some
fall under the new genera about to be proposed. Thus, /. plana Hall, M. alata Ulrich
and_perhaps MtruncataHall, belong to Hurymya; M. oviformis Ulrich, to Modiolodon;
M. subelliptica Ulrich, to Allodesma; M. cincinnatiensis Hall and Whitfield, M. pulchella
Ulrich, M. cancellata Walcott, M. oblonga Ulrich, M. pholadiformis Hall, and M. superba
Hall to Actinomya; M. gesneri Billings and M. trentonensis Hall, to Endodesma. M.
nasuta Conrad, sp., and M. subnasuta Meek and Worthen, belong to Orthodesma, Hall
and Whitfield, and M. carinata Hall, possesses all the essential characters of Goni-
ophora, Phillips. Of Upper Silurian species MW. recta Hall, from the Niagara of Wis-
consin, is a Matheria, while the M. dicteus of the same author and locality, and M.
primigenia Conrad, sp., of the Medina, have slender cardinal and posterior lateral

teeth of the Cyrtodonta type.

Moprovorsis sruitis Ulrich.
PLATE XXXVI, FIGS. 1 and 2; PLATE XLII, FIG. 19.
1892. Modiolopsis similis ULR1cu. Nineteenth Ann. Report, Geol. Nat. Hist. Sur, Minn., p. 225.
Shell of medium size, obliquely elongate ovate, highest in the posterior half,
contracted at the beaks to between one-half and three-fifths of the greatest hight.
Hinge line nearly straight, about half as long as the shell posterior to the beaks.
Anterior end small, neatly rounded; ventral margin gently convex, nearly straight

LAMELLIBRANCHIATA. 505

Modiolopsis consimilis.]

in the middle: posterior end broadly rounded, slightly produced and more strongly
convex in the lower half, the upper more gently curved and sometimes forming an
obtusely angular junction with the hinge line. Beaks about one-seventh of the entire
length of shell behind the anterior extremity, rather small, incurved, projecting
moderately above the hinge; umbones compressed in the cast, a little less so in the
shell. Surface moderately convex, most prominent along the umbonal ridge, the
latter a little stronger than usual for species of this genus. Cardinal slope concave.
A broad and comparatively well-defined mesial depression extends obliquely across
the shell from the beak and, expanding, causes the straightening of the ventral mar-
gin. Excepting in this part the shell is very thin, and the anterior muscular scar,
which is comparatively of small size, is scarcely distinguishable in casts. Surface
rather obscurely marked with numerous fine concentric lines and a few stronger
varices of growth.

As might be expected, this early species exhibits features intermediate between.
those marking the group of forms which I now propose to distinguish as A¢timomya-
‘and true Modiolopsis. This is seen in the thin shell and consequent indistinctness
of the anterior adductor impression, in the full and prominent umbones and
the convex rather than straight or concave basal line. At first I was inclined to.
put the species into the new genus, but later comparisons have shown that Aetire—
wyd Was at that time already well established and that J/. similis belongs to the line
which finally produced M. modiolari ws. Then the comparatively strong mesial depres-
sion indicates Modiolopsis and not Meera -

Compared with Minnesota Trenton species, all the others referred to Modiolopsis
are narrower posteriorly. The Actinomy ya super ba Hall, sp., has a larger anterior
end, the postero-basal margin more produced, and the umbones larger. The
undescribed Kentucky species referred to in the original description proves to be
a Cyrtodonta closely related to C. subovata Ulrich.

Formation and loality.—Middle third of the Trenton shales at Minneapolis, Minnesota.

Mopionopsis (?) CONSIMILIS, . sp.
\ PLATE XLII, FIGS. 17 and 18.

This shell is so much like M. similis that at first I belheved it might belong
to the same species. Carefully compared, however, it proved to differ in several
characters that are more important than striking. The umbones are larger
and very little compressed, and the mesial sulcus, which is a well marked
feature in that species, is scarcely distinguishable. The outline also is a little
different, the posterior hight being relatively somewhat less than in the preced-

ing species.

506 THE PALEONTOLOGY OF MINNESOTA.

(Modiolopsis oweni

This species ought, perhaps, to go with ype meats rather than Modiolopsis, but
as I have so far seen only the exterior of the shell, and therefore know nothing of
the internal characters, it seemed best to refer it to Modiolopsis provisionally, because
' of a general resemblance to M. similis. I wish to say further, that I would not -be |
surprised if the shell proved to have the hinge of a Cyrtodonta, several species of
which it resembles quite as much as it does Modiolopsis.

Formation and locality.—Near the base of the Trenton formation, Murfreesboro, Tennessee.

MoproLopsis OWENI, 7. sp.

PLATE XLII. FIGS. 15 and 16.

This species is founded upon a single and not very well preserved cast of the
interior. It seems to belong to Modiolopsis and very near M. similis, with which
species it should be compared. As far as can be seen its valves were a little more
convex, the mesial sulcus narrower, the anterior part of the shell somewhat inflated
and the posterior part comparatively narrower.

Formation and locality.—Galena shales, about five miles south of Cannon Falls, Minnesota.

“MoproLopsis ARGUTA, 7. Sp.
PLATE XXXVI, FIGS. 3—6.

Shell small, ventricose, elongate, highest posteriorly, the length twice the
greatest hight, and three times the hight at the beaks. Cardinal margin straight;
anterior end unusually long, sharply rounded at the extremity of the hinge beneath
which it slopes backward gradually curving into the straight ventral margin; poster-
ior end strongly convex and most prominent in the lower half, above curving more
gently and very gradually into the dorsal edge. Beaks a little more than one-sixth
of the length from the anterior extremity, moderately prominent and incurved, com-
pressed; mesial impression scarcely more than a mere flattening of the sides of the
shell; umbonal ridge rather sharply rounded. Point of greatest convexity of valves
very near the center. Surface with concentric lines, sharp, subequal and thread-
like on the cardinal slopes, here with about ten in 5 mm. at their strongest parts,
becoming faint before they pass over the umbonal ridge in their course to the
anterior end where they are again somewhat thread-like. In good casts of the
interior the anterior adductor sears are large, prominent, and marked on their inner
halves with transverse lines. The surface markings do not show through the shell
so as to mark the casts. Hinge thin, apparently edentulous. An average specimen
is 24 mm. long, the largest seen about 31 mm.

This is one of a number of closely related species ranging from the lower Trenton
to the middle beds of the Cincinnati group. They are all elongate, especially so for

LAMELLIBRANCHIATA. 507

Modiolopsis nana.)

Modiolopsis, anterior to the beaks. Their general expression, therefore, is decidedly
like Orthodesma, of which some member of this line is believed to have been the
ancestor. In Orthodesma the valves gape slightly at the ends, which is not the case
in these shells. In that genus again the point of greatest thickness is more or less
behind the center, while in all the species referred by me to Modiolopsis this point is
central or anterior to the center. Furthermore, as stated under the generic descrip-
tion, the VW. arguta line traces by very gradual degrees into M. concentrica H. and W.,
which is a Modiolopsis in every respect.

M. nana, of the Galena shales, has stronger concentric striz, and these extend
further forward and are visible on the internal cast, is scarcely so convex, with a
deeper mesial depression and more obtuse umbonal ridge, and more rounded and
shorter anterior end; M. mytiloides Hall, is without the even thread-like lines on the
cardinal slope; and M, angustata Ulrich, of the Cincinnati rocks, has a more truncate
posterior margin, more uniformly rounded anterior end, and more nearly parallel
dorsal and ventral margins.

Formation and locality.—Middle third of the Trenton shales, Minneapolis, St. Paul, Chatfield and
Fountain, Minnesota.

Mus. Reg. No. 8350.
MopIoLopsis NANA, %. Sp.

PLATE XXXVI, FIG. 7.

This small species is closely related to M. arguta.- The differences are as follows:
The valves are not quite as convex, the umbonal ridge is less sharply rounded, the
mesial depression a trifle deeper, and the anterior end a little shorter and more
uniformly rounded. The most striking peculiarity, however, is found in the con-
centric lines which show very distinctly on casts of the interior, are coarser (eight
in 5 mm.), more regular and continue of the same strength over the cardinal slope,
umbonal ridge and forward into the mesial depression, near the center of which
they are lost. 7

In M. mytiloides Hall, as identified in Minnesota, the surface of the casts is very
obscurely marked with concentric lines, and the posterior extremity of the hinge
line subangular.

Only two specimens have been seen. Of one the length is 19 mm., the posterior
hight 9.3 mm., the anterior hight 7.2 mm., the thickness 6 mm. Of the other these
dimensions are respectively 16, 8, 6 and 5 mm.

Formation and locality —Galena shales, near Cannon Falls, Minnesota.

508 THE PALEONTOLOGY OF MINNESOTA.
(Modiolopsis mytiloides.

MoproLtopsis mytiLtorpEs Hall.
PLATE XXXVI, FIG. 8.

Modivlopsis mytiloides HALL, 1847. Pal. New York, vol. i, p. 157.

Three incomplete casts of the interior are referred to this species. They agree
very well with Hall’s description and figures, except in being proportionately higher.
But the general appearance of his figure 4a, particularly in the abruptness of the
postero-basal curve, causes me to believe that the original of the figure has been
compressed vertically and is therefore narrower than normal.

- Compared with M. arguta and M. nana, which are closely simulated, it is found
to differ in its surface markings, which are fine, with stronger wrinkles of growth,
the latter showing only on casts; the concentric lines are, therefore, not equal nor
thread-like. The outline differs in the subangular junction of the posterior and
cardinal margins. The mesial depression also is more pronounced and the end of
the casts in front of the depression more swollen, causing a slight concavity in the

ventral margin.

Formation and locality.—Trenton limestone, Middleville, New York; middle Galena, Goodhue and
Fillmore counties, Minnesota, and Oshkosh, Wisconsin. According to Billings, in the Trenton and Black
River groups of Canada. J

Mus. Reg. No. 8361.

MopioLopsis CHATFIELDENSIS, %. Sp.

PLATE XXXVI, FIGS. 9 and 10.

Shell small, subelongate, the length a little less than twice the hight. Dorsal
and ventral margins nearly straight, subparallel, diverging slightly posteriorly;
anterior end rather long, rounded; posterior margin broadly rounded, scarcely
oblique, curving gradually into the hinge line. Beaks compressed, projecting little,
situated about one-fourth of the entire length from the anterior extremity. Valves
moderately convex, thickest at the middle, the umbonal ridge sharply rounded in
the upper half; mesial flattening distinct, very gently concave. Surface of cast
exhibiting rather broad and unequal concentric furrows which, on the shell itself,
seem to have separated sharply-elevated lines. The latter were probably restricted
to the cardinal and posterior slopes. Anterior adductor scar large, its inner edge
sharply defined and curving forward. Hinge apparently thin and edentulous.

Length 10 mm., posterior hight 5.2 mm., anterior hight 4.5 mm., thickness 3.38 mm.

This species is not elongate, like the M. angustata Ulrich, of the Cincinnati rocks,
its anterior end is shorter and the sides of the valves flatter; with a better defined
umbonal ridge than in M. subparallela Ulrich, also occurring in that higher series of
strata at Covington, Kentucky. Compared with Minnesota species, it is perhaps

LAMELLIBRANCHIATA. 509

Modiolopsis obsoleta.]

nearest M. arguta, with which it is also associated. It is, however, readily distin-
ugished by its surface markings, which are not visible on the casts of that species,
and by its less oblique anterior and posterior ends and more nearly parallel ventral
and dorsal margins. In M. faba Hall, which is probably not a true Modiolopsis, the
mesial depression is much more distinct. M/. nana is wider and more oblique pos-

teriorly, and has more regular surface markings.

Formation and locality—Middle third of the Trenton shales, Chatfield, Minnesota.

Mop1oLopsis OBSOLETA, 2. Sp.

PLATE XXXVI, FIGS. 11 and 12.

Shell small, elongate ovate, the length twice the greatest or posterior hight.
Valves thickest a little above the center, rather uniformly convex, the umbonal
ridge and mesial depression being both nearly obsolete. Beaks small, between one-
fourth and one-fifth of the entire length from the anterior extremity. Dorsal margin
gently arcuate, anterior end narrowly but almost uniformly rounded, ventral edge
straight, posterior end slightly oblique, rather broadly rounded, most prominent a
little beneath the center, above which it curves forward gradually into the hinge
line. Surface with very fine concentric lines; these are equal and strongest near the
posterior cardinal border. Hinge very thin, edentulous. Muscular scars not observed.

Length 13.3 mm., posterior hight 6.6 mm., anterior hight 5 mm., thickness (left
valve only) about 2.5 mm.

Considerably like, and probably a near relative of M. arguta, but differs in the
more uniform convexity of its surface, obsolete umbonal ridge and less oblique
anterior margin. The posterior end also is comparatively narrower and the shell
smaller. Avisterella nitidula is associated but cannot be confounded, since it is a
smooth shell, with unequal valves, and much wider posteriorly.

Formation and locality.—Associated with Plethocardia wmbonata, Matheria rugosa and other species
marking the upper part of the middle third of the Trenton shales near Cannon Falls, Minnesota.

Moproxtopsts concava Ulrich.
PLATE XXXVI, FIGS. 15, 16, 16a:

Modiolopsis concava ULRicu, 1892. Nineteenth Ann. Rep. Geoi. Nat. Hist. Sur. Minn., p. 227

Shell very small, elongate, the greatest hight a little less than the length,
arcuate, the posterior end much the widest and broadly rounded, the anterior end
exceedingly short, narrow and contracted beneath the beaks; the latter are small,
compressed, and project but little above the hinge. Hight of posterior third about
two and one-half times as great as at the beaks. Dorsum gently arcuate ; anterior

two-thirds of ventral margin strongly concave, a fact due in a great measure to the

510 : THE PALEONTOLOGY OF MINNESOTA.

{[Modiolopsis concentrica

width of the mesial sulcus and the rapid descent of the surface included in it.
Umbonal ridge slight, cardinal slope, convex. Ina dorsal view the anterior half of
the shell appears compressed, yet the point of greatest thickness is very near the
middle of the length. Surface marked with simple concentric lines of growth.
Hinge plate very thin, without teeth or appreciable thickening under the beak.
Muscular scars not observed.

This peculiar species, which is decidedly mytiloid in appearance and probably
not a true Modiolopsis, is distinguished at once from all known Lower Silurian
Lamellibranchiata, except M. arcuata Hall, by its strongly arcuate form, Hall’s
species is represented as larger and with a straight instead of convex back.

Formation and locality —Same as the preceding.

Moptonopsis concentrica Hall and Whitfield.
* PLATE XXXVII, FIGS. 15 and 16.
Modiolopsis concentrica HALL and WHITFIELD, 1875. Pal. Ohio, vol. ii, p. 86.

Shell rather exceeding medium size, elongate ovate, highest in the posterior
half. Hinge line arcuate, gently declining toward the extremity and rounding gradu-
ally into the oblique posterior margin, the same curve continuing to the lower third
when it is sharpened in turning forward into the basal margin. The latter is gently
convex in the posterior half and anterior third, the part between being very slightly
concave. Anterior end very short, narrowly rounded. Beaks small, compressed,
projecting very little above the hinge. Surface of valves moderately convex, most
prominent a little in front of and above the middle; this point is on the umbonal
ridge, which is low, broadly rounded, and not a conspicuous feature. Mesial sulcus
shallow, forming an undefined depression across the valves from the beak to the
middle third of the basal margin. Surface marked on the cardinal slope and poste-
rior end by regular, even, concentric furrows, four to six of them in 5 mm. in their
strongest parts. These furrows are most distinct along a line following the middle
of the cardinal slope; in crossing the umbonal ridge they become suddenly obsolete,
existing On the sides, basal portion, and anterior end only as fine irregular strize of
growth.

In casts of the interior the concentric furrows are distinctly visible on the
posterior half of the cardinal slope. The mesial sulcus is much deeper and rather
sharply defined on the posterior side by a strongly convex ridge extending obliquely
across the cast from a point a short distance behind the beaks toward the basal
margin, which, if the ridge did not become obsolete before reaching it, would he
intersected at a point about three-fifths of the length of the shell behind the anterior
extremity. In front of this ridge the surface is impressed and flattened to the

LAMELLIBRANCHIATA. 511

Modiolopsis excellens ]

strongly elevated filling of the anterior adductor scar. The latter is large, of oval
shape, horizontally marked in its upper half; sharply defined all around and, because
of the brevity of the anterior end, is situated partly beneath the point of the beak.
Posterior scar large, but so faintly impressed that its exact shape cannot be deter-
mined with the material at hand. Pallial line distinct only in the anterior half,
where it consists of an obscurely pustulose raised line.

To this species I refer provisionally a badly distorted mould of the exterior of a
right valve, collected by me at Spring Valley in 1887. Its surface is marked
precisely as described above, but the reference is still rendered doubtful by the fact
that its anterior end is a little longer than is normal for the species. There is, how-
ever, no reason to doubt that M. concentrica occurs in Fillmore county, and it is to
draw attention to its probable occurrence in Minnesota that the species has been
included in the report.

Formation and locality.—A common species in the upper beds of the Cincinnati group at numerous
localities in Ohio, Indiana and Kentucky. Probably also in the Hudson River shales near Spring Valley,
Minnesota.

MoDIOLOPSIS EXCELLENS, 2. Sp.

PLATE XXXVI, FIGS. 13-14.

This species, of which we have five specimens, is closely related-to—AW. concentrica
Hall and Whitfield, and was at first confounded with it. A careful comparison
however proved its distinctness in the following respects: It attains a larger size,
the casts are more uniformly convex, with the mesial sulcus, on both the shell and
the cast, much shallower, for which reason the ventral margin is very slightly
convex where it is sinuate in that species. The outline differs also in the postero-
cardinal region being less uniformly curved and more prominent at the extremity
of the hinge. The anterior end is longer so that a line drawn from the point of the
beak across the shell at right angles to the hinge line passes within the inner border
of the anterior adductor scar, whereas it cuts a third of the scar away in JZ. concen-
trica, Finally, the concentric surface markings are finer and the difference between
them as developed on the cardinal slopes and on the sides of the shell is a much
less striking feature. The number of the concentric lines at a point about midway
between the beaks and the posterior extremity varies in different specimens from
six to nine in 5 mm.

What I regard as a nearer ally occurs at the top of the Cincinnati hills. The
outline of this species is intermediate between figures 6 and 15 of plate xxxvi. In
its characters also it approaches one almost as nearly as the other.

Formation and locality.—Upper part of the Hudson River group, Spring Valley and Granger,
Minnesota.

Mus. Reg. No. 8374.

4

512 THE PALEONTOLOGY OF MINNESOTA.
(Eurymya.

Genus HURYMYA, n. gen.
Modiolopsis (part.) HALL and ULRICH.

Shell thin, short, compressed, high and subalate posteriorly, greatly narrowed
anteriorly, transversely truncate-ovate or subtriangular in outline. Cardinal margin
straight, base oblique, gently convex. Beaks small, near the anterior extremity.
Umbonal ridge moderate, rounded or subangular. No mesial sulcus, the surface of
the valves forward and downward from the umbonal ridge being slightly convex or
flat rather than concave. Hinge strong, with a broad longitudinally striated liga-
mental area posterior to the beaks, and beneath them an obscure cardinal fold or
tooth in the left valve and a corresponding depression in the right. Muscular
impressions and pallial lie apparently as in Modiolopsis.

Type: Modiolopsis plana Hall.

The alate appearance of the postero-cardinal region, rounded base, absence of a
mesial depression, and the presence of a striated ligamental area are the principal
distinguishing features when compared with Modiolopsis. The anterior part of the
‘hinge is precisely as in Modiomorpha, Hall, but the Devonian shells, upon which that
genus is founded, have no posterior striated ligamental area, while in nearly every
other respect they agree with Modiolopsis. The new genus Modiolodon has one or
more strong cardinal teeth in both valves, no ligamental area, and a mesial thicken-
ing of the inner sides of the valves that produces mesial sulci on the casts.

Besides the type only one other species has been described that I would place in
this genus without question. This is the Modiolopsis alata Ulrich, from the hill quar-
ries at Cincinnati, Ohio. <A third form, if it is really distinct from H. plana, occurs
in the middle beds of the Trenton in Kentucky and @ennessee. A possible fourth

‘species is the Modiolopsis truncata Hall, a rare shell of the Cincinnati rocks. This

species is known only from indifferently preserved casts of the interior. So far as

4 these admit of judgment, the species might well be classed with Hurymya. Of the

‘hinge nothing is known beyond this, that it was stronger than usual for Modio-
lopsis.
EKurymya pLana Hall.
PLATE XXXVI, FIGS. 27 and 28.

Mgdiolopsis plana HALL, 1861. Rep’t. Sup’t. Geol. Sur. Wis., p. 30; Geol. Wis., vol. i, pp. 88 and 438,
fig. 6; Ubricn, 1892, Nineteenth Ann. Rep. Geol. Nat. Hist. Sur.
Minn., p. 224.
Shell rather small, compressed, subtriangular in outline, alate and highest
posteriorly, the greatest hight and length (the latter measured parallel with the

hinge line) respectively as six is to seven. Cardinal margin straight, nearly as long
g s s g

LAMELLIBRANCHIATA. 513

Modiolopsis nana.]

as the shell; anterior end very small, sharply rounded above, curving backward into
the slightly convex, medially almost straight, basal margin; posterior edge gently
curved, truncate, nearly vertical, strongly convex below; above turning abruptly
into the hinge line. Beaks small, but little incurved, not prominent, about one-
sixth of the length of the shell behind the anterior extremity. Umbonal ridge mod-
erate, cardinal slope flat or slightly concave, ventral and anterior slopes depressed
convex. Surface marked with distant strong concentric lines of growth, and between
these with a finer set. In casts of the interior the anterior muscular impression is
well marked, not very large, vertical, situated in front of the beaks and close to the
cardinal margin. A little more than one-third of the scar is divided off above by a
distinetly impressed transverse line. Posterior scar indistinct, much larger than the
anterior, situated behind the center of the posterior cardinal slope. Pallial line simple,
rather distinct, not following the outline of the shell, being farther removed from the
margin in the postero-basal region than elsewhere. Hinge as shown in figure 28 on
plate xxxvi. Free casts of the interior of both valves, being without the hinge
plate, are longer in proportion to the hight than are the impressions of single valves.

The shape of the shell will distinguish this species at once from all Minnesota
Lamellibranchiata except Matheria rugosa and Cyrtodonta affinis, both of which occupy
a higher horizon and have a different shell structure.

I have before me ten more or less complete silicified shells from the middle Tren-
ton or “Orthis beds” of Tennessee and Kentucky. These belong to a species that is
closely allied to 2. plana and which may be called Hurymya subplana, n. sp. The new
species does not attain the size of the Minnesota form, and is not so high and more
oblique posteriorly, while the margin is less narrowly rounded in the postero-basal
region. The Cincinnati species, 4. alata (Modiolopsis alata Ulrich) is a slightly
shorter and more compressed shell, with a more convex basal margin and different

anterior muscular sear.

Formation and locality—Lower limestone of the Trenton formation in Minnesota at Minneapolis,
St. Paul and Cannon Falls. In Wisconsin the species seems to be restricted to the ‘‘ Lower Blue”
limestone at Janesville, Beloit and Mineral Point.

Mus. Reg. Nos. 749, 757, 5011, 5012, 5013, 5062, 5358, 5669, 5834, 8312.

ae \
NV psALiatv-egz4a
wy

Genus ACFENOAFYA, n. gen.
Modiolopsis (part.), of various authors.

Shell ovate, more or less elongate, narrowing anteriorly. Valves moderately
ventricose, fitting each other tightly. Anterior end short, but not excessively so.
Base gently convex, occasionally straight, never sinuate. Mesial sulcus wanting.

—33

514 THE PALEONTOLOGY OF MINNESOTA.

[Actinomya.

Beaks comparatively large, full and rather prominent. Umbonal ridge generally
strongly rounded, sometimes subangular. Surface with concentric lines of growth
and often with radii or divaricating folds; the radii sometimes restricted to the
inner side of the shell, showing on casts of the interior and not on the exterior of
the shell itself. Muscular scars and pallial line as in Modiolopsis, excepting that in
the majority of the species they are very faintly impressed. Hinge plate edentulous,
very narrow, especially so under the beaks, a little wider and grooved on each side
for the reception of a linear internal ligament. A similar external ligament prob-
ably also present.
Type: Modiolopsis cincinnatiensis Hall and Whitfield.

Fig. 39. ea, a large right valve of Actinomya cincinnatiensis, mostly devoid of shell, showing the
muscular scars and delicate internal radii on the cast; b, the hinge of another right valve of the same
species: ¢ and d, hinges of a left and a right valve of Actinomya pholadiformis Hall, sp. The student
will do well to compare these hinges with those of Modiolopsis and related genera, figured on a suc-
ceeding page.

This genus brings into very natural association a number of Lower Silurian
species, the described forms of which have heretofore been placed chiefly with
Modiolopsis. These are Modiolopsis cincinnatiensis H. and W., M. cancellata Walcott,
M. pulchella Ulrich, and two undescribed species from the lower or Utica horizon of
the Cincinnati group, 4: subcarinata, 0. sp., from the Galena, and Modiolopsis superba |
Hall, M. modioliformis Meek and Worthen, and Orthodesma saffordi Ulrich, from
the lower limestone of the Trenton formation.

Besides these, I propose to place here another group of species, so far known
only from rocks above the Trenton, that approaches Modiolopsis in the strength and
definition of the anterior adductor impression, while differing from that genus, and
therein giving us a clue to their origin, in the convexity of the basal outline and
absence of a mesial depression or so-called “byssal sulcus,” and in the character of
the hinge, which is thinner, and thus more like that of an Orthodesma than of species
of Modiolopsis of the same size. Four species of this kind, all from the Cincinnati
rocks, are known to me, only two of them, however, being described, 7. e., Modiolopsis
pholadiformis Hall, and M. oblonga Ulrich.*

Whilinw tA : 7 —

*Mr. S. A. Miller has described three forms having surface markings like setinomye pholadiformis. These may be
distinct from Hall’s species, but I cannot now admit that they are. The one called M. sulcata is ulmost certainly founded
upon vertically compressed specimens of the pholadiformis, while the M. corrugata is, so far as IT can make it out, in no
wise different from the same species.

LAMELLIBRANCHIATA. 515

Actinomya modioliformis.]

The systematic position of Actinomya seems to be nearly intermediate between
Orthodesma and Modiolopsis, differing from the former in the somewhat shorter form
and tightly closing instead of gaping valves, from the latter in the thinner hinge
plate and_shell, and from both in the convex basal outline and absence of a mesial
sulcus.

WhAr areata.
Aormemya MoDIOLIFORMIS Meek and Worthen.

PLATE XXXVI, FIGS. 19 and 20.

Modiolopsis modioliformis MEEK and WoRTHEN, 1868. Geol. Sur. Ill., vol. iii, p. 294.
Compare Modiolopsis superba HALL, 1861. Rep’t., Sup’t. Geol. Sur. Wis., p. 31.

Shell of medium size, elongate, obliquely ovate, much the widest in the posterior
half; strongly convex. Hinge nearly straight, rather short, extending anterior to
the beaks almost half as far as posterior to them, and posteriorly less than half the
distance from the beaks to the posterior extremity of the shell. From the hinge
the outline passes almost imperceptibly into the oblique posterior margin, and this
slopes backward with a gentle convexity to the abruptly rounded posterior basal
extremity. Basal margin extending obliquely upward and forward, very slightly
convex throughout its length. Anterior end narrow, rounding sharply into the
extremity of the hinge. Beaks rather prominent, incurved, situated about one-sixth
of the entire length of the shell from the anterior extremity; a strongly rounded or
subangular umbonal ridge extends from the beaks to the posterior extremity of the
shell, the convexity becoming gradually less as it recedes from the beaks. Surface
with fine concentric strie and rather strong (especially on the flattened regions
anterior to the umbonal ridge) wrinkles of growth. Muscular impressions so faint
that they cannot be traced with certainty on the casts of the interior at hand.

I believed this species to be identical with Hall’s previously described Modio-
lopsis superba, but Prof. R. B. Whitfield, to whom a specimen was sent for compari-
son with the original types of Hall’s species, writes me that it is “less angular on
the umbonal ridge, more rounded on the base, and fuller on the lower disc.” These
differences are probably of specific importance. Figure 20 is taken from the type
used by Meek and Worthen. The specimen, though a good one, is slightly distorted
by vertical pressure, and imperfect in front and along the base. To facilitate com-
parison with fig. 19, the missing parts have been restored in the figure.

This fine species I regard as in every sense an Actinomya. It is, perhaps, nearer
A saffordi Ulrich, than any other known, but there is little likelihood of confusion
between them, that species being a higher shell, with a larger anterior end and
somewhat smaller umbones. It has also several radiating folds on the posterior

cardinal slope not seen in this species,

516 THE PALEONTOLOGY OF MINNESOTA.

[Actinomya subcarinata,

Formation and locality.—Lower part of the Trenton formation at Beloit and Mineral Point, Wis-
consin. Not yet known to have been found in Minnesota, but there is no reason why it should not
occur in the limestone at Minneapolis, St. Paul and elsewhere in the state.

Mus. Reg. No. 8341.
Whttavreatar
SUBCARINATA, %. SD.

PLATE XXXVI, FIGS. 17 and 18.

Shell of the same general form as 4. modioliformis M. and W. sp., only smaller,
not so oblique, subalate and higher posteriorly and consequently not so elongate. The
hinge also is longer, the posterior margin more erect and the junction between them
subangular. The postero-basal margin, furthermore, is not so sharply rounded, while
the beaks are less incurved and farther apart,. Surface of cast entirely smooth except
between the umbonal ridge and the postero-cardinal border, where a number of very
fine radiating striz are obscurely visible.

This species reminds somewhat of the New York Trenton Modiolopsis avicu-
loides of Hall (Pal. N. Y., vol. i, p. 161; 1847), but I cannot believe they are identical.
Indeed, it is more likely that they will prove widely distinct. I know of no Minne-
sota species with which it might be confounded.

Formation and locality.—Rare in the shaly part of the middle Galena of Goodhue county, Minnesota.

Genus ORTHODESMA, Hall and Whitfield.

Orthodesma, HALL and WHITFIELD, 1875. Pal. Ohio, vol. ii, p. 93.

Shell elongate, usually increasing slightly in hight posteriorly. Anterior end
comparatively long, contracted in front of the beaks. Valves moderately convex,
usually with a strong umbonal ridge and a broad mesial depression in front of it,
their edges fitting tightly along the straight or sinuate ventral margin, but leaving
a narrow gape at each end. Umbones prominent, wide, compressed, often extending
posteriorly as low cardinal ridges between which the hinge is sunken. Hinge plate
edentulous, very thin, long, extending in almost a straight line from the posterior
cardinal angle, past the beaks, nearly to the anterior extremity of the shell. Liga-
ment linear, internal and external, the latter chiefly. Posterior muscular scar large,
very faint, elongate ovate; anterior scar large, though scarcely half the size of the
posterior, well defined, ovate or approaching semicircular in shape, the vertical
diameter the longest. Pallial line simple. Shells thin, marked externally with
more or less distinct concentric striz and wrinkles.

Type: Orthodesma rectum Hall and Whitfield.

The above diagnosis does not agree exactly with Hall and Whitfield’s original
description of the genus, but as it corresponds with the fossils no apology is neces-

~)

LAMELLIBRANCHIATA. 51
Orthodesma.]

sary. They make, for instance, the erroneous statement that the hinge plate is bent
down in front of the beaks; and the fictitious feature has become so well established
in literature that it stands as the most important peculiarity of the genus, indeed, as
the only one separating it from Orthonota, Conrad. Now, despite the fact that the
hinge plate is nearly or quite as straight in Orthodesma as in Orthonota, IT am fully
satisfied that there is little affinity between the two jen a The Lower Silurian
genus, doubtless, is closely related to Modiolopsis and “Coma Not so, however,
with the Devonian genus, which seems to me to be totally different and nearer_Solen
than Modiolopsis.

Species have been placed under Orthodesma that are very different from the
types, some of them belonging, I believe, to other families. Thus, O. byrnesi §. A.
Miller, and 0. mickleboroughi Whitfield, belong to Rhytimya, a new genus that obvi-
ously belongs to the same family as Pholadella, Hall, and Allorisma, King. 0. cunei-
forme Miller, has recently been made the type of his new genus Sphenolivm. This
genus seems to be related to Cuneamya and therefore cannot belong to the Modio- .
lopside. O. subovale Ulrich, together with a number of undescribed species, belongs to.
’ the new genus Psiloconcha, while O. saffordi Ulrich, should be referred to ‘Actinomyt.

ORTHODESMA MINNESOTENSE Ulrich.
PLATE XXXVII, FIGS. 12 and 14.

Orthodesma minnesotense ULRICH, 1892. Nineteenth Ann. Rep. Geo. Nat. Hist.Sur. Minnesota, p. 228.

Shell small, elongate, subrhomboidal, with the dorsal and ventral margins nearly
straight and parallel; the length two and one-half times the width. Beaks small,
incurved, compressed, projecting moderately above the hinge and situated about one-
fourth of the entire length from the anterior extremity; posterior umbonal ridge
subangular, cardinal slope abrupt, in casts of the interior with a linear impression
close to and on each side of the hinge line. ‘Anterior end small, contracted a little
in front of the beaks, almost uniformly rounded; posterior end oblique, sloping
upward and forward from the produced and narrowly rounded lower part.

Interior with the anterior pair of muscular scars rather distinctly marked and
large; above and between them and the beaks, two other very small pairs of scars
are to be seen on the specimen figured above, but the posterior muscles left no
appreciable impressions. Surface of casts with few obscure folds of growth.

This shell is related to O. curvatum Hall and Whitfield, though more nearly
approaching 0. contractum Hall, in its outline. It differs from both in having the
posterior end narrower and in wanting the strong concentric furrows which occur
on the posterior cardinal slopes of those shells.

Formation and locality—Middle third of the Trenton shales, St. Anthony Park, St. Paul, Minnesota.

518 THE PALEONTOLOGY OF MINNESOTA.

LOrthodesma schucherti.

OrTHODESMA SCHUCHERTI, ”. Sp.

PLATE XXXVI, FIGS. 25 and 26.

Shell only moderately elongate, subovate, between two and two and one-half
times as long as wide; cardinal and basal margins nearly straight, gradually diverg-
ing posteriorly to near the posterior end, where the hight is equal to once and a half
times the hight at the beaks; posterior margin obliquely truncate above and rather
strongly rounded in the lower half; the anterior end, though narrowly rounded, is
still a little wider and shorter than usual for the genus. Umbones not prominent,
less so than usual, compressed; beaks incurved, a little less than one-sixth of the
length of the shell from the anterior extremity; umbonal ridge subangular and a
well marked feature above, becoming obtuse and at last indistinguishable as it is
traced to the postero-basal margin. Mesial sulcus undefined, obsolete, the surface
anterior to the umbonal ridge being scarcely flattened. Surface with a very fine
and a stronger set of concentric lines. Anterior muscular impression large, well
defined, the inner side somewhat straightened, giving it a semicircular shape.|:

This species, which, in the absence of a mesial sulcus, recalls Actimomya, is still
so much like Orthodesma in all other respects that its generic position cannot be in
doubt. Indeed, excepting the feature mentioned, the species is very similar to
O. recta, the type of the genus. That species is more elongate and narrower poster-
iorly, and has oblique folds on the cardinal slope not seen on the Minnesota form.

The specific name is given in honor of Mr. Charles Schuchert, who found the
only specimen seen.

Formation and locality.—Middle Galena, Weisbach’s dam, near Spring Valley, Minnesota.
Mus. Reg. No. 8343.

OrTHODESMA SuBNASUTUM Meek and Worthen.
PLATE XXXVI, FIGS. 23 and 24.

Modiolopsis subnasuta MEEK and WORTHEN, 1870. Proc. Phila. Acad. Nat. Sci., p. 41; 1875, Geol.
z Sur. Ill., vol. vi, p. 494. (Not Modiolopsis subnasuta Hall, 1860.)
Modiolopsis carrollensis WORTHEN, 1882, Bull, No. 1, Ill. St. Mus. Nat. Hist.

Shells rather small, elongate, narrow and slightly arcuate, the length a little
more than two and one-half times the greatest posterior hight and more than three
and a half times the hight at the beaks. Valves rather strongly convex, the most
prominent part being on the well defined umbonal ridge a little behind and above
the middle of the valves. Dorsal and ventral margins slightly diverging posteriorly,
the former very gently arcuate, the latter with an equally slight and broad sinuosity
chiefly anterior to the middle. Anterior end narrow, produced, rather sharply rounded

LAMELLIBRANCHIATA. 519

Orthodesma subnasutum.]

posterior edge obliquely truncate, very gently convex above the narrowly rounded
basal part and passing rather abruptly into the hinge line. Beaks not prominent, com-
pressed, situated between one-fifth and one-sixth of the length of the shell behind the
anterior extremity. Surface of cast showing moderately distinct irregular concen-
tric undulations, which are most strongly defined on the umbonal ridges and on the
flattened or concave flanks. These are crossed on the cardinal slopes by two obscure
sulci. Anterior muscular scar moderate in size and definition, ovate; small pedal
muscular scars distinct above them.

The valves of this shell gape very slightly posteriorly and probably also in front,
but upon this point the material at hand presents no conclusive evidence. They
have also the point of greatest convexity a little behind the center. Both of these
features are characteristic of Orthodesma. On the other hand the species presents
considerable resemblance to the early elongate forms of Modiolopsis like M. arguta,
but this indicates, I believe, merely, what I have already stated, a common origin
for the two genera and not that 0. subnasutwm was evolved from the Modiolopsis. I
come to this conclusion because the present species is even nearer the O. minnesotense
which occurs in the same beds holding M. arguta. Further, as regards the develop-
mental history of Orthodesma, I view O. minnesotense and O. subnasutum as the earliest
known stages in the line of development that produced 0. cwrvatum H.and W., and
one or two undescribed species occurring at Cincinnati, Ohio, while O. rectum H. and

W., appears to have been derived through intermediate species from 0. schucherti.
Specifically O. swbnasutum is distinguished from O. minnesotense by its more
elongate and posteriorly diverging form, better defined mesial depression, the longi-
tudinal sulci on the cardinal slope, and more distinct concentric folds.

As regards the name of the species, it will be seen from the synonomy that
Meek and Worthen first called it Modiolopsis subnasuta, being evidently unaware
that the same name had been used previously by Prof. James Hall (Can. Nat. and
Geol., vol. v, p. 148; 1860) for an Upper Silurian species from Canada. This fact
being brought to the notice of Prof. Worthen he, in 1882, proposed to change the
name to Modiolopsis carrollensis, and this specific designation will have to be used
should the Canadian species also prove to be an Orthodesma. But until that has been
established, the original name will have a clear field.

Formation and locality—The types of the species are from the Galena of Carroll county, Illinois.

The specimen here figured and described is from the same horizon near Dixon, Mlinois. In Minnesota
the species is to be looked for in the “Maclurea beds” of the Galena.

or
iw)
S

THE PALEONTOLOGY OF MINNESOTA.

[Orthodesma canaliculatum,

ORTHODESMA CANALICULATUM, v.s,

PLATE XXXVII, FIGS. 7—11.

Shell elongate, the length three times the hight; cardinal and basal margins
straight, nearly parallel; posterior margin oblique, rounding into the hinge line, below
which it slopes backward with a gentle curve to the postero-basal extremity where
it turns abruptly into the basal line; anterior end contracted in front of the beaks, of
moderate length, rounded, most prominent a little above the middle. In a side view
the beaks project very little, are compressed by a broad shallow sulcus which crosses
the valves and occupies a large part of the anterior three-fifths of the shell; umbonal
ridge rather distinct, extending from the beaks to the postero-basal extremity. In
a cardinal view of casts of the interior, the only condition in which the species has
been noticed, the hinge line is strongly depressed, lying at the bottom of a wide and
deep channel, deepest between the rather widely separated beaks and gradually
shallowing posteriorly. Casts usually almost smooth, exhibiting only a small num-
ber of obscure concentric furrows. One specimen preserves a small part of the shell
and this shows that near the dorsal edge the outer surface is marked with somewhat
regular raised lines, about six of them in 5 mm. The best preserved casts exhibit in
the posterior half of the mesial sulcus a number of obscure radii. Anterior muscular
scar sharply defined at the inner side, rather small, broad-oval or circular, occupying

the middle two-fourths of the upper half of the anterior end. Posterior impression
"somewhat larger than the anterior, subcircular, with a narrow prolongation extend-
ing forward nearly parallel with the posterior cardinal margin. Pallial line distinct
in the anterior half, consisting (on the casts) of a straight row of obscure pustules
extending in a slightly oblique direction from the base of the anterior adductor
impression toward a point much wearer the ventral border.

There are several peculiar features about this species. (1) I have never seen its
valves separate, a fact indicating, if it is not fully accounted for by the next circum-
stance, a strong ligament. (2) Its natural position seems to have been with the
anterior end down, and so it is commonly found in the shales, and in consequence
it is often greatly shortened by pressure. (3) The channel-like depression of the
hinge; and (4) the unusual course of the anterior half of the pallial line. These
peculiarities distinguish the species readily from all others of the genus known.

Formation and locality—Hudson River group, Spring Valley, Minnesota. Fragments have been

found at many localities in Ohio and Indiana where the upper beds of the Cincinnati formation are
exposed. Good specimens, however, are very rare,

LAMELLIBRANCHIATA. 521
Modiolodon,

Genus MODIOLODON, n. gen.

Cyrtodonta (part.) SAFFORD, 1869, Geol. of Tenn.; Modiolopsis (part.), ULR1cH, 1890, Amer. Geol.,
vol, v.

Ovate shells of the same general type as Modiolopsis and Modiomorpha, but hay-
ing from one to three oblique cardinal teeth in each valve.

Type: Modiolopsis oviformis Ulrich.
The hinge in this genus is much like that of Ischyrodonta, Ulrich, and 1 might have
placed the species under that genus were it not for the fact that their shells are of
the same composition as those of Modiolopsis, while the shells of that genus are gen-
erally heavier and of the more calcareous nature characterizing the Cyrtodontide.

The development of distinct cardinal teeth is an important deviation from
Modiolopsis, and 1 cannot see how any one could object to the generic separation
of species possessing them. Surely, if Modiomorpha can stand, then Modiolodon must,
for its claims for recognition are certainly better. This may be seen from the accom-
panying sketches of the hinges of the three genera.

Fig. 40. Hinges of Modiolopsis, Ifodiomorpha and Modiolodon. a, anterior half of hinge of a
right valve of Modiolopsis versaillensis Miller, from the upper part of the Cincinnati group at Versailles,
Indiana. 6, hinge of a right valve of Modiolopsis valida, a new species from the top of the Lower
Silurian at Waynesville, Ohio. This species, though closely related to M. modiolaris, has a wider hinge
plate than in any other species of the genus known. c¢, hinge of a left valve of Modiomorpha concentrica
Conrad, sp., from the Hamilton of New York. d, anterior part of hinge of right valve of Modiolodon
ganti (Cyrtodonta ganti Safford}, e and f, of right and left valves of Modiolodon winchelli (Cyrtodonta
winchelli Safford), and g, of a left valve of Modiolodon oviformis Ulrich; all from the middle Trenton
(“Orthis beds”) of Wilson county, Tennessee, and from specimens kindly given to the author by Prof,
J. M. Safford.

Modiolodon ganti and M. winchelli, two of the most typical species of this genus,
were placed into the genus Cyrtodonta, Billings, by Prof. Safford. Aside from their
different shell structure, they have no right in that genus, being without posterior

lateral teeth,

MopioLopON PATULUS, 7”. Sp.
PLATE XXXVII, FIGS. 20—24.
Shell of medium size, suberect, compressed convex, broad ovate, very inequi-

lateral; anterior end very short, in the casts occupied almost entirely by the strongly
elevated, lobe-like, anterior muscular scar. Hinge line short, the posterior part of

522 THE PALEONTOLOGY OF MINNESOTA.
° {Modiolodon (?) gibbus.

the cardinal region compressed and rounding, except in the youngest stages, gradu-
ally into the posterior margen. Beaks small, rather prominent, scarcely incurved
in the shell and not at all in the casts. Surface of casts almost uniformly convex.
Pallial line distinct along the anterior and ventral margins, not traced posteriorly;
nor has the posterior muscular scar been observed. Hinge with two interlocking
cardinal teeth in the left valve, and corresponding sockets and teeth in the right.
This shell is wider, more erect and more uniformly convex than M. oviformis,
the type of the genus. The erectness of the beaks is a very unusual feature among
the Modiolopside and should render good service in the identification of the species.

Formation and locality.—Middle Galena, Kenyon, Goodhue county, Minnesota, and Decorah, Iowa;
also in the Trenton near Danville, Kentucky. Rare.

Mus. Reg. No. 8363.

MoproLopon (?) GIBBUS, 2. Sp.
PLATE XXXV, FIGS. 28 and 29.

Shell small, obliquely ovate, the anterior end very small, separated as a bicarin-
ated lobe from the body of the shell by a distinct sulcus extending vertically across
the valves from the anterior side of the beaks. Behind this sulcus the valves are
gibbous, especially in the umbonal region and anterior to the center; posterior
cardinal region somewhat compressed; beaks full, prominent, incurved. Surface
with simple concentric lines of growth, rather stronger in the sulcus than else-
where. Hinge very thin immediately under and behind the beaks. It widens some in
front of them, and here the left valve exhibits a small protuberance. Being a small
shell, and the specimen not very well preserved, the nature of this protuberance has
not been determined with certainty. Examined under a good lens it looks like the
remains of a double tooth. Muscular scars and pallial line not observed.

This species cannot be confounded with any Lower Silurian bivalve known to
me. The small size and peculiar character of the anterior end, and the unusual
gibbosity of the shell, render its systematic position doubtful. I place it with
Modiolodon chiefly because the outline is much like that of M. patulus, but I
suspect strongly that it belongs to an undescribed genus.

Formation and locality.x—Upper third of the Trenton shales near Cannon Falls, Minnesota.

Genus COLPOMYA, n. gen.

Shell subelongate, oblique, inequilateral, subrhomboidal or ovate in outline,
widest posteriorly or with the ventral and dorsal margins nearly parallel. Mesial

; LAMELLIBRANCHIATA. 523
Colpomya.]

sulcus distinct, causing a flattening of the umbones and a sinus in the ventral mar-
gin. Umbonal ridge prominent, strongly convex. Hinge plate straight, long, very
thin posterior to the beaks, much heavier in front of them; beneath the beak of the
right valve a tooth-like prominence which fits into a corresponding depression
beneath the beak of the left valve; in front and beneath this depression in the
left valve, a strong process projects obliquely downward, backward and toward the
opposite valve, and is partly received in a socket that defines the anterior ‘side of
the tooth in the right valve, while its lower end curves under that tooth. Muscular
sears and pallial line apparently as in Modiolopsis, excepting that there is a small
accessory scar in the hinge plate just behind the anterior adductor,as in Ischyrodonta.
Type: Colpomya constricta n. sp.

Fig. 41. Colpomya constricta Ulrich, top of Trenton group, Frankfort, Kentucky. a, right valve,
showing the usual characters of the species; b, interior of a left valve; ¢, interior of an imperfect
right valve.

Colpomya evidently belongs to the Modiolopsidw with relations to Modiolopsis, Mo-
diolodon and Orthodesma. In none of those genera, however, are the umbonal ridges
and the mesial sulci quite such marked features, at any rate it would be rare, so that
we may fairly regard their distinct development in shells of this family as indicative
of Colpomya. When we come to internal characters all comparisons with the first
and last of these genera may as well cease, since in both the hinge is practically
toothless. In Modiolodon, however, we find cardinal teeth, but every one will admit
that they are very different from those of the genus under consideration. There is
nothing to represent the oblique process which projects under the tooth and hinge
plate of the right valve, the teeth being approximately equal in the two valves of
Modiolodon.

The species to be placed ino this genus are not numerous and with two possible
exceptions are all new. The exceptions are Modiolopsis milleri Ulrich, from the
Cincinnati rocks, and M. faba Hall, said to be a Trenton and Hudson River species.
The general expression of these shells is very much as in undoubted species of Col-
pomya, but as their hinges are not yet known, their removal from Modiolopsis now
would be of very doubtful advantage. Of four new species, C. demissa is a lower
Trenton form, while the type of the genus and two other species occur in the
upper Trenton of Kentucky.

or
bo
—

THE PALEONTOLOGY OF MINNESOTA.

[Aristerella.
COLPOMYA DEMISSA, 2. Sp,

PLATE XXXVI, FIGS. 21 and 22.

Shell small, gibbous, arcuate, subtriangular, very high posteriorly; hinge line
very slightly arcuate, nearly as long as the shell, forming an angle where it joins
the nearly erect and broadly rounded posterior margin; ventral margin abruptly
rounded and much produced in the posterior third, then ascending rapidly with a
broad yet distinctly concave curve into the narrow anterior end, which is most
prominent above where it turns sharply into the hinge line. Beaks of moderate
size, compressed, incurved, about one-sixth of the length of the shell from the
anterior extremity; umbonal ridge prominent, strongly rounded, curved. Mesial
sulcus broad and deep, occupying the greater portion of the ventral slope. Cardinal
slopes slightly concave, somewhat compressed and alate posteriorly. Surface with
distinct subequal concentric striz. Hinge and interior unknown.

The prominent umbonal ridge and deep mesial sulcus are the characters that
have induced me to place this peculiar little shell with Colpomya. Compared with
the other species of this genus, it will be found to differ in the much greater hight
of its posterior end. Of Minnesota species only Modiolopsis concava is at all similar,
but even here there is scarcely a possibility of confusion, that species being more
elongate, its anterior end much narrower and the posterior outline quite different.

Formation and locality.—Middle third of the Trenton shales, Chatfield, Minnesota.

Genus ARISTERELLA, n. gen.

Shell small, almost smooth, subovate, moderately convex, inequivalved, the left
valve smaller than the right. No mesial sulcus. Muscular and pallial impressions
as in Aclinomyt. “Hinge plate apparently very thin and edentulous.

This Sans | is f founded upon a single species, which might have been placed into
either eee or Eurr ‘ymya were it not for its unequal valves.

ARISTERELLA NITIDULA, ”. Sp.

PLATE XXXV, FIGS. 30—39,

Shell small, 5 to 8 mm. long, subovate, narrowest anteriorly; hinge line nearly
straight, long; posterior margin slightly oblique, broadly rounded, subangular at the
extremity of the hinge; basal margin gently convex, ascending into the narrowly
rounded anterior end. Beaks situated about one-fifth of the length of the shell from
the anterior extremity, small, projecting slightly above the hinge, and that of the

LAMELLIBRA NCHIATA. 525

BEndodesma.]

right valve beyond that of the left. Umbonal ridge inconspicuous. Surface of shell
smooth, nothing but an occasional growth line having been detected on any of the
specimens seen. A good cast of the interior shows that the pallial line and muscular
scars are very faintly impressed; the anterior scar is small, ovate, and situated in
front of the beaks close to the hinge line; the posterior scar at least twice as large
and situated just behind the center of the cardinal slope. As shown in figs. 33 and
35, the relative convexity of the two valves varies, the thickness of the left in some
specimens being only half as great as that of the right, while in others it is quite
two-thirds. A slight gap is left between the posterior edges of the valves.

J am not acquainted with any Silurian shell with which this species might be
confounded. Several small species of Modiolopsis and Colpomya demissu are associ-
ated with it, but they can all be distinguished without the slightest trouble.

Formation and locality.—Middle third of the Trenton shales, Chatfleld, Minnesota.
Mus. Reg. No. 8450.

Genus ENDODESMA, n. gen.

Shell elongate, the dorsal and ventral margins subparallel, equivalved, generally
ventricose. Mesial depression deep, often producing a decided oblique contraction
of the shell and a sinus in the basal outline. Umbones compressed, elevated consid-
erably above the hinge line on the anterior side, but not on the posterior side. Hinge
thin, apparently edentulous. A strong linear internal ligament was attached on
each side to a rib or ridge. Back of shell flattened or with the edges of the valves
bent inward without, however, forming a true escutcheon. More or less well defined
lunule in front of the beaks. An obscure sulcus in the middle of the cardinal slope.
Shell very thin; surface marked with concentric growth lines. Muscular scars and
pallial line so faintly impressed that they have not been determined satisfactorily.

Type: Endodesma cuneatum, n. sp.

This well marked genus is placed in the family Modiolopsidw chiefly in deference
to the views of Hall, Billings, and Meek and Worthen, who have each described a
species as belonging to Modiolopsis. According to my own conviction there is little
indeed to suggest that genus, the shape of the shell being often quite different (in
this respect some of the species remind of Orthodesma) and the mesial depression
deeper, while the faintness—so far as can be seen the total absence—of muscular
scars on casts of the interior is not only a striking but an important difference. In
the faintness of the muscular impressions the new genus agrees with the most typ-
ical forms of Actinomya, but they are distinguished at once by their want of a mesial
contraction, in consequence of which their basal outlines are gently convex instead

526 THE PALEONTOLOGY OF MINNESOTA.

[Endodesma cuneatum.

of sinuate. LHndodesma finally is separated from all true Modiolopside by the lunule
in front of the beaks and the sulcus and ridge on each side of the hinge line.

A more natural placement of the genus seems to me to be near Rhytimya,
Ulrich, which is regarded as an early type of the Pholadellidw. But as Endodesma
evidently is a complex primitive type with characters suggesting widely different
Lamellibranchiata it is probably good policy to defer coming to a final conclusion
as to its position until we know more of the origin of the group of species and its
development in times succeeding the Trenton to which all the species now known
are restricted.

Six species of Hndodesma are illustrated in this work. Besides these, Modiolop-
sis? trentonensis (Conrad) Hall, is almost certainly also referable to the genus.

ENDODESMA CUNEATUM, nN. sp.
PLATE XXXVI, FIGS. 33, 34.

Shell elongate, the length and greatest hight, which is subcentral, respectively
as nine is to four. Valves strongly convex, the point of greatest thickness on the
umbonai ridge above and in front of the center; cuneate posteriorly. Dorsal mar-
gin gently arcuate, passing rather gradually into the posterior outline; the latter is
prominent and sharply rounded near the middle, nearly straight in the upper half
and slightly convex below; ventral margin gently convex in the posterior half,
straight or barely sinuate near the center of the anterior half, and rather strongly
convex in front; anterior end short, most prominent and narrowly rounded in the
middle, very slightly concave in the upper half. Beaks of moderate size, strongly
incurved, with a rather distinct lunette beneath them; mesial sulcus clearly defined;
umbonal ridge unusually prominent, subangular near the beaks. Cardinal slope
abrupt, concave, in casts of the interior showing a well marked curving depression
and ridge on each side of the hinge line. Surface of cast with a few obscure con-
centric folds. Anterior muscular scar very faint, situated just within the anterior
extremity of the shell, of semielliptical shape, the inner side straight.

This species must be closely related to L’. trentonense Hall sp., from the Trenton
of New York, but in the figure of that species the anterior end is quite different,
being shorter and obliquely truncate. The anterior end of the Minnesota form is
more like that of the Canadian H. gesneri Billings, sp., but in other respects these
two species are quite distinct.

Formation and locality.—The specimen figured, which is the only one seen, was discovered by Dr. C.

H. Robbins in the middle Galena near his home at Wykoff, Minnesota, and kindly given to the author for
description.

LAMELLIBRANCHIATA. 527

Endodesma orthonotum.]

ENDODESMA POSTLATUM, 2. Sp.
PLATE XXXVII, FIGS. 5 and 6.

Of this species I have seen only a single imperfect specimen—which under
ordinary circumstances would scarcely merit description. Being however the most
recent existence of the genus now known it is of interest as it may give usa clue to
the later development of the genus. As may be seen from the figures the species is
closely related to EF. cuneatum but, as the name implies, the posterior width (hight)
is greater in L/. postlatum. Ina cardinal view both ends also are more obtuse, giving
greater convexity to the sides; the umbonal ridge, though prominent, is not so
sharply rounded, the umbones fuller, the anterior end shorter, and the posterior
margin more broadly rounded and most prominent in the basal half instead of near
the middle. Finally, the mesial sulcus crosses the valves more obliquely and the
sinuation of the ventral margin is wider and nearer the center of the length of the
shell.

The side view of this shell is considerably like that of several species of Modio-
lopsis, but the absence of a strong anterior muscular scar on casts and the presence

of the concave areas bordering the hinge line proves that it is not a Modiolopsis but
an Hndodesma.

Formation and locality.—Uppermost beds of the Galena, Dubuque. Lowa, where if was collected by
Mr. Charles Schuchert.

Mus. Reg. No. 8345.

EnpoprEsMa ortHoNoTUM Meek and Worthen.
PLATE XXXVII, FIGS. land 2.

Modiolopsis orthonota MEEK and WorTHEN, 1868, Geol. Sur. LIl., vol. iii, p. 295.
Modiolopsis rectiformis WORTHEN, 1882, Bull. No. 1, Ill. St. Mus. Nat. Hist., p. 38.

Shell elongate, the length being nearly three times the hight; valves quite
convex, the greatest convexity being a short distance above the middle, in front of
which they have an undefined concavity commencing in the umbonal region and
widening and deepening to the base in front of the middle. Cardinal margin long,
very nearly straight or but slightly arched; posterior margin obliquely substrunca-
ted, sometimes very faintly sinuous above, and rather narrowly rounded below the
middle; basal margin subparallel to the dorsal, gently convex behind the middle,
and broadly sinuous between the middle and the front; anterior side short, con-
tracted beneath the beaks, narrowly rounded. Beaks depressed, appearing on a line
with the dorsal margin, strongly incurved, placed about one-sixth of the entire

length of the valves behind the anterior extremity; lunule rather large but not

528 THE PALEONTOLOGY OF MINNESOTA.

(Endodesma orthonotum,

sharply defined. In the cast the dorsal edge from the beaks to near the posterior
extremity of the hinge appears bent inward and downward. Surface marked with
moderately distinct concentric strie of growth, crossed on the dorsal slope by an
obscure sulcus, extending obliquely from the posterior side of the beaks to the mid-
dle of the obliquely subtruncated upper part of the posterior margin.

Length about 64 mm., greatest posterior hight 22 mm., anterior hight 21 mm.,
convexity 20 mm. °

The above description is founded upon the original type of the species which is
preserved in the Illinois State Museum. The obscuring matrix of which the authors
of the species complain was removed without much trouble and a good cast pre-
pared. The figures on plate 37 were drawn from this counterfeit of the type and
and give a reliable idea of the species, which most certainly cannot be said of Meek
and Worthen’s illustration.

Comparing the species as it is now known with other forms of the genus Endo-
desma we find that it is one, and the earliest, of three closely related forms which at
first seemed scarcely distinguishable. As usual, however, with such hasty conclu-
sions their error soon became manifest when careful comparisons were undertaken,
so that now I may say that they are not only separable but with ease even when
the specimens are complete. Thus the second of these species—the next
described, E. undosum--is distinguished from Meek and Worthen’s species by its
irregularly undulating surface, more distinct growth lines, and uniformly rounded
posterior margin. The third species, H. gesneri Billings’ sp., is nearer than E.
undosum, but as a comparison of figures 1, 2,3and 4 on plate 87 will show, there
is in this case even little trouble in drawing the specific lines. Meek and Wor-
then in distinguishing H. orthonotum from the Canadian species seem to have
relied chiefly upon the more central position of the point of greatest. convexity
in their species, but this difference is much less in the specimen of 4. gesnert
here illustrated.* We must therefore depend upon other differences among which
I find one that seems to be well marked, namely, the anterior extremity of L.
gesneri is subangular while in E. orthonotum it’ is almost regularly rounded. Car-
rying our comparison to other points we find that in the latter the upper pos-
terior edge is more truncated, the dorsal outline somewhat straighter, and the
valves on the whole more convex and a little longer.

I have rejected Worthen’s name rectiformis because under Hndodesma the

specific name orthonotum is not preoccupied as was the case under Modiolopsis.

*In Billings’ figure 45 b (Paleozoic Fossils, vol. i, p. 43) this point is so far behind the center that I am constrained
to believe the figure overdrawn or the specimen abnormal in this respect.

LAMELLIBRANCHIATA. 529

Fndodesma undosum.]

Formation and locality.—Lower Trenton limestone, Dunleith, Illinois. There is reason to believe
the species occurs in Minnesota and it will be well to search for it in the limestone at Minneapolis and
St. Paul. If £. gesneri occurs in the rocks of the state it will most probably be in the middle division of
the Galena.

ENDODESMA UNDOSUM, 2”. Sp.
PLATE XXXVI, FIG. 38.

Shell of the same general form as EZ. orthonvtum M. and W., sp., being elon-
gate, with the length a little more than twice and a half the hight; dorsal and
ventral margins subparallel; posterior edge almost uniformly rounded; anterior
end short, narrowly convex. Beaks depressed, wide, strongly incurved; umbonal
ridge inconspicuous; mesial depression undefined, wide, rather shallow. Lunule
narrow but shaply defined. Ridge and sulcus rather distinct in the anterior half
of the posterior dorsal slope of casts. Surface of casts with numerous strong and
somewhat irrregular concentric lines of growth; on the dorsal slope and umbonal
ridge a number of large and very irregular undulations or depressions.

This species is distinguished from F. gesneri Billings, sp., and EF. orthonotum M.
& W. sp., by its stronger lines of growth, the irregular surface undulations, and
more uniformly rounded posterior margin.

Formation and locality.—‘‘Upper Buff Beds” of the Trenton formation, one and a half miles west
of Beloit, Wisconsin, where it was collected by Mr. Charles Schuchert.

Mus. Reg. No. 8344.

ENDODESMA COMPRESSUM, 2. Sp.
PLATE XXXVI, FIGS. 35 and 37.

Shell elongate, dorsal and ventral margins subparallel, the length two and one-
half times the hight. Anterior margin concave above, most prominent and suban-
gularly bent down at the middle, beneath which point the upper part of the
gradual curve into the basal line is nearly vertical; ventral outline very broadly
sinuate; posterior margin oblique, most prominent and strongly rounded in the
lower half, above passing rather gradually into the hinge line. Beaks compressed,
mesial depression or sulcus illy defined but very wide, causing the sinuosity of
the ventral margin to extend farther posteriorly than usual. Umbonal ridge
rather sharply defined on the upper side by the distinctly concave character of
the dorsal slope. Dorsal edge inflected, the inflected part extending rather far
inward under the beaks (see fig. 37). Lunule narrow, deep and well defined.
Surface of cast with a few obscure concentric undulations.

This species seems to be more nearly related to HL. gesneri Billings, sp., than

to any of the others. It is however readily distinguished by the broader sinuosity
—34

530 THE PALEONTOLOGY OF MINNESOTA.

LPsiloconeha.

of the ventral margin, more compressed dorsal regions, sharper umbonal ridge,
and somewhat different posterior outline. The central and posterior parts of the
shell also are less convex.

Formation and locality.—Middle Galena, near Wykoff, Minnesota.

Genus PSILOCONCHA; n. gen.

Shell elongate subelliptical, compressed convex, gaping slightly at both ends;
inequilateral, with very small beaks, inconspicuous umbonal ridges and smooth or
concentrically lined surface. Mesial depression very shallow or wanting; basal
outline convex. Shell very thin; hinge plate very narrow, edentulous. Ligament
internal? linear. Muscular impressions exceedingly shallow, rarely distinguishable.
Anterior adductor scar small, subcircular or ovate, situated in front of the beaks
and just within the hinge line. Posterior adductor about three times the size of
the anterior, occupying the greater part of the middle third of the space between
the beaks and the posterior extremity of the shell. Pallial line simple, more dis-
tinctly impressed in the posterior half of the shell than in the anterior.

Type: Psiloconcha grandis Ulrich.

Fig. 42. a. and b, the left side and a dorsal view of an excellent cast of the interior of Psiloconcha
grandis, n. sp., from the upper beds of the Cincinnati group, at Waynesville, Ohio. c. a right valve
retaining the shell, and d. the right side of an internal cast of Psiloconcha elliptica, n. sp., from the same
horizon at Clarksville, Ohio, and Richmond, Indiana.

The systematic position of this genus is doubtful. That it does not belong
to the Modiolopside I am satisfied, but where else to place it seemed a question
whose solution it was deemed best to defer till we shall have learned a little
more about certain Devonian and Carboniferous shells. Species of Psiloconcha,
in their gaping ends and general expression, remind greatly of Carboniferous
shells that are gommonly referred to the recent genus Solenomya, but I cannot
bring myself to believe that the short end of the Lower Silurian species is the
posterior, as would be the case if they were related to Solenomya. Indeed, it
appears to me far from established that this is true even of the Carboniferous forms
referred to. .

LAMELLIBRANCHIATA. ball

Psiloconcha minnesotensis, }

My conviction that Psiloconcha does not belong to the Modiolopside rests partly
upon the resemblance just noticed, but more especially upon a difference in the
composition of the shells. That some difference, whatever its nature, really existed
a comparison of the fossils will render obvious at once. Thus, I have collected
from the same bed of shale species of Modiolopsis, “Letinomya, Orthodesma and
Psiloconcha. The shells of the first three genera were coated with either a black
or dark brown film, while those of the last matched the color of the shales or were
a few shades lighter.

A single and not very typical species occurs in the Galena of Minnesota. At
least seven and probably eight species are found at various horizons in the Cin-
cinnati group. Two of these are figured on the preceding page and one was
described by me in 1879 as Orthodesma subovale (Jour. Cin. Soc. Nat. Hist., vol. 2, p.

82). The others I hope to describe in the next report of the Geological Survey of
Ohio.

PsILOcONCHA MINNESOTENSIS, ”. Sp.

PLATE XXXVI, FIGS. 31 and 32.

Shell rather small, moderately elongate, highest posteriorly, the length about
twice the greatest hight. Hinge line straight, nearly as long as the entire shell;
anterior end rounded, much narrower than the posterior; basal margin gently and
uniformly convex; posterior end subtruneate above, slightly produced and strongly
rounded in the lower half. Valves rather strongly convex for the genus, the great-
est convexity in front of and above the middle. Beaks small, situated between one
fifth and one sixth of the length of the shell behind the anterior extremity. Um-
bonal ridge subangular in the rostal region and unusually prominent for the genus.
Anterior to the ridge the surface of the shell is gently convex. Cardinal slope
slightly concave, abrupt near the beaks. Surface marked with fine concentric lines
which are thrown into obscure folds in crossing the umbonal ridge. Internal char-
acters unknown.

This species is doubtfully referred to Psiloconcha. It differs from all the other
species of the genus in its greater convexity, proportionally narrow anterior end, and
comparatively prominent umbonal ridge. I might have placed it with Sphenolium,
Miller, but the shell is not sufficiently ventricose, the umbones are too small, and
there is no lunule in front of the beaks, while a slight gap separates the edges of
the valves at the ends.

Formation and locality.—Middle Galena, Pleasant Grove, Minnesota.

532 THE PALEONTOLOGY OF MINNESOTA.

[Prolobella.
Genus PROLOBELLA, n. gen.

Shell equivalved, moderately convex, very inequilateral, obliquely acuminate-
ovate. Anterior end very small, auriculate or subnasute, sharply distinguished from —
the body of the shell. Basal and posterior margins rounded. Hinge thin, apparently
edentulous, rather short and not produced at the posterior extremity; just in front
of the beaks a short clavicle-like process produces a sharp linear depression in casts.
of the interior. Surface marked with concentric lines of growth and radial striz or
plications. Anterior adductor scar small, situated in the anterior lobe. Posterior
impression and pallial line not observed.

Type: Prolobella striatula, n. sp.

It is almost certain that Conrad’s Avicula trentonensis and aviformis, which Hall
in 1847 united as one species, are congeneric with the Minnesota species which is
made the type of this new genus. These shells are not true Aviculide, their valves
being equal and without the prolonged posterior wing. Nor do they fit much better
into any of the other families. They seem to be remnants of one of those complex
primitive types that give the systematist so much trouble to classify. In this case
there is almost as much reason for placing the genus with the Ambonychiude as
with the Aviculide or the Modiolopside. With such types it is good policy to defer
conclusions until the collector has furnished us with the missing links. And they

will be found sooner or later, for the lower paleozoic rocks are teeming with undis-
covered fossils.

PROLOBELLA STRIATULA, 2. Sp.
PLATE XXXYV, FIG. 27. |

Shell rather small, obliquely subovate, moderately convex. Anterior end very
small, somewhat auriculate, narrowly rounded, and rather sharply distinguished
from the rest of the shell. Cardinal margin straight, about half as long as the
shell posterior to the beaks, passing with a gentle curve into the posterior margin,
which is oblique and moderately convex to the lower third where the outline bends
rapidly forward; basal margin almost uniformly convex; anterior outline strongly
sinuate beneath the ear. Beaks full, slightly prominent, not much incurved, just
in front of them the cast shows a vertical linear depression extending from the
hinge half across the narrow sinuate part of the shell. Umbonal ridge inconspicu-
ous. Surface with a small number of obscure concentric lines, and in the antero-
basal third with numerous very fine thread-like radiating strie.

This species cannot be confounded with any other Minnesota bivalve known.

From P. trentonensis Conrad, sp. of the Trenton of New York, it is readily distin-

LAMELLIBRANCHIATA. 533
Orytodontidz.]

guished by its greater hight, different outline, and finer radiating strie. The latter
are also most distinct in that species centrally where they are wanting entirely in
P. striatula.

Formation and locality.—Middle Galena, Pleasant Grove, Minnesota.

Family CYRTODONTID A, n. fam.

Shells commonly ovate or rounded, rarely elongate, valves generally ventricose
or strongly convex. Shell substance calcareous, without epidermis, usually thick.
Hinge plate often massive, strong, with from one to five cardinal teeth; elongate
posterior lateral teeth usually present, but may be wanting. Ligament chiefly
external. Anterior adductor scar strongly impressed, rather large though always
smaller than the much more faintly impressed posterior adductor. Pallial line
simple.

The genera included in this family seem to form a very natural group. With
one exception, Ptychodesma, Hall, a Devonian genus, they are all restricted to the
Lower and Upper Silurian rocks and many of the species rank among the most
important fossils of the various beds in which they occur. The individuals also are
often very abundant, while their preservation is on an average better than that of
any other group of paleozoic bivalves.

The principal genera are variously placed by systematists, but the Arcide have
been most favored. The conclusions of the authors seem to have been biased by a
supposed resemblance between the hinges of Cyrtodonta and Macrodon and to
Stoliezka the relation is so obvious that he is led to say “the former may be consid-
ered as the predecessor of the latter in geological history.” Now, after careful
examination, I am obliged to dissent in so for at least as to claim that the case is
far from proved. So far as we can now tell the last species of Cytodonta (Upper
Silurian) are as far removed from Macrodon as are the earliest, while the first
species of Macrodon (Devonian) is no nearer Cyrtodonta, than are the Jurassic forms.
Even should later discoveries prove a development of the latter from the Silurian
genera under consideration, it would not settle the question for it is not by any
means an established fact that Macrodon is genetically related to Arca.

There is something decidedly suggestive in the resemblances to be noted in a
comparison of the interiors of true Arcide like those of the genus Barbatia, Gray,
and certain species of Ctenodonta, Salter. Now if these should, as I am inclined to
believe, indicate something more than a merely accidental agreement of structure,
I should hold that Macrodon was not a member of the Arcide, since that genus
most certainly did not arise in Ctenodonta.

w

534 THE PALEONTOLOGY OF MINNESOTA.

[Cyrtodonta,

The Cyrtodontide seem to me to be a family of shells that is essentially Lower
Silurian, the Upper Silurian species being both few in number and of small size
and thin-shelled. Indeed the evidence at hand goes to show that the family
became practically extinct with the close of the Upper Silurian. [If this is true
then we cannot very well ally them with recent families of shells, and as they con-
stitute an easily recognized group of genera it has been deemed necessary to estab-
lish a new family for their reception.

The Cyrtodontide, despite the well developed dentition prevailing among the
typical members, seem to represent a very early type of structure, and one that
probably antedated both the Ambonychiidae and Modiolopside, to which also they
appear to be more closely related than to any other of the contemporaneous
families. Thus certain of the earliest species of Vanuxemia (e. g. V. terminalis)
greatly resemble true Ambonychia, while the majority of the Modiolopside present,
aside from the hinge, an internal conformation of parts that is decidedly like the
prevailing appearance in the present family. Perhaps the only constant difference
between the shells of these three families is that while those of the Ambonychiide
and Modiolopidw were provided with a well develeped epidermis those of the
Cyrtodontide preserve no trace of such a covering.

Genus CYRTODONTA, Billings.

Cyrtodonta, BrLLiInGs, 1858, Can. Nat. and Geol., vol. 3, p. 431.

Palearca, HAut, 1859, Pal. N. Y. vol. iii, p. 27; also 12th Rep. Reg. N. Y. Mus. Nat. Hist., p. 10.

Angellum, S. A. MILLER, 1878, Jour. Cin. Soc. Nat. Hist., vol. i, p. 105.

Cypricardites, HALL, and most American authors, (not of CONRAD).

Shell varying from transversely or obliquely ovate to subcircular, moderately
ventricose. Beaks prominent, rather tumid, incurved, situated in the anterior third,
fourth or fifth of the shell. Surface marked with concentric lines of growth. No
lunule nor escutcheon. Hinge plate strong, nearly straight, often with a narrow
and not sharply defined ligamental area. Cardinal teeth well developed, subequal,
generally obliquely curved, sometimes nearly horizontal, two to four in each valve,
situated mostly in front of the beaks. Posterior lateral teeth usually two or three in
each valve, strong, elongate, more or less curved and slightly oblique, situated near
the extremity of the hinge. Adductor muscular scars placed immediately beneath
the two sets of teeth, both subovate, the posterior very faint, the anterior only
moderately impressed. Pallial line simple.

Types: C. rugosus and C. canadensis of Billings.

This is an excellently defined genus and one of the largest of the paleozoic
genera of Lamellibranchiata. It is also pre-eminently a Lower Silurian genus, the

or

: LAMELLIBRANCHIATA. 53!
Cyrtodonta ]

Upper Silurian forms now referred to it bring but impoverished remnatts of the
powerful stock that preceeded them.

Many species have been placed under Cyrtodonta or Cypricardites, which is
usually considered as identical, that have no right there. Thus of forty-nine species
classed as Cypricardites by S. A. Miller in the 1889 edition of his North Amer. Geol.
and Pal., only eleven can with reasonable certainty be said to belong to Cyrtodonta.
These are C. breviuscula, canadensis, huronensis, rugosa, spinifera and subcarinata, all
described by Billings, C obliqua Meek and Worthen, and C. obtusa, saffordi, subangu-
lata and subspatulata of Hall. The remainder belong to Whitella, Ortonella, Vanuc-
emia and Modiolodon, or are too little known for positive generic placement.*

To the eleven species mentioned we must add seven that have been described

since the publication of Mr. Miller’s list; also fifteen new species, of which ten are
published in this work. This makes a total of twenty-six valid Lower Silurian
species positively known to have the characters of the genus as above defined.
Two Upper Silurian species, Modiolopsis dicteus Hall and M. primigenia Conrad, sp.,
also fall under Cyrtodonta. These have unusually thin shells but their hinges are
essentially as demanded for the genus.
A few remarks are necessary to explain my adoption of Cyrtodonta instead of
Conrad’s Cypricardites as the name for this genus. Conrad’s name has seventeen
years priority over that proposed by Billings, but it was not until 1859 when Hall
reproduced a sketch of the hinge that had been overlooked among the manuscripts
left by Conrad that any adequate idea of his genus was possible. In the mean
time (1858) Billings proposed and fully illustrated his genus Cyrtodonta. In the
following year Hall published (in Pal. N. Y., vol. iii, p. 27, and 12th Rep. Reg. N. Y.
State. Mus., p. 10) his genus Palwarca in which he proposed to include precisely the
same group of shells. In the museum report mentioned (p. 13) Hall reproduces
Conrad’s sketch of the hinge of Cypricardites with the remark that both the descrip-
tion and figure of that genus as given by Conrad correspond in many respects with
Palwarca and “should an examination of the typical species prove the two identical
the later name will give place to that of Cypricardites”. Finally in a supplemen-
tory note to vol. iii (p. 524) he again uses this cut and now adopts Cypricardites in
place of his Palearca and Billings’ two genera Cyrtodonta and Vanuxemia. I have
not noticed that the Canadian geologists have given up the use of Cyrtodonta. In
the United States however, with a few exceptions all use Cypricardites instead,
while of European authors Bigsby adopted Palwarca and the majority of the others
Cyrtodonta.

*The following belong to Whitella: hindi and plebeia of Billings; megambonus and quadrangularis of Whitfield; sterlingensis
Meek and Worthen; and ventricosa of Hall. The new geners Ortonella is founded upon C. hainesi S. A. Miller. C, hayniana
Safford, and niota, rectirostris and rotundata Hall, belong to Vanuxemia, while ©. ganti and winchelli of Safford belong to the
new genus Modiolodon.

536 THE PALEONTOLOGY OF MINNESOTA.

[Oyrtodonta subovata.

The above is a fair statement of the case as I found it when I began the
present work. Had my studies shown what both Billings and Hall conceded to be
the case, that Conrad’s sketch of the hinge of Cypricardites was identical with that
of Cyrtodonta and Palearca, 1 would most surely have sided with Hall and adopted
the oldest name. But here was the rub. Comparisons with the hinges of numerous
species of this family of shells have demonstrated beyond question that Conrad’s
figure and description of the hinge of Cypricardites does not correspond exactly
with that of any true Cyrtodonta or Vanuxemia known. He represents the cardinal
teeth as diverging from the beak much as in a Lyrodesma and says that the anterior
one is the “largest and most prominent”. Neither of these conditions is ever
present in Crytodonta. On the contrary the teeth are subparallel, and to be called
horizontal rather than radial, while the anterior one, if any can be so called, is the
smaller. Nor have I seen any Cyrtodonta with five cardinal teeth, the usual
number being three; two is not uncommon, but four is very rare.

We are now confronted with the question, did Conrad correctly describe and
illustrate the hinge of his genus? This question can be determined only by a study
of the type of the genus. But here again we meet with trouble for of the sixteen
species originally referred to the genus only one, his C. curtus remains, the others
having proved generically distinct, being now referred to other genera. The genus
must then, if it stands at all, be based upon C. curtus. I do not know whether the
hinge drawn by Conrad represents that of this species or not. For the present we
must assume that it does, and further, until we know the contrary, it must be
accepted as correct. From this standpoint then it is evident that Cyrtodonta and
Cypricardites are not synomymous, and that both may stand for the present. I
would suggest that, however the question may be eventually terminated, Cypricar-
dites may for a long time to come serve as a convenient temporary receptacle for

those species which because they are insufficiently known cannot be definitely
placed into other genera.

‘

CyRTODONTA SUBOVATA, 2. Sp.

PLATE XXXIX, FIGS. 28, 29, 31-33, ? 30 and ? 45.

Shell somewhat obliquely ovate, narrowest anteriorly. Dorsal margin short,
less than half the length of the shell posterior to the beaks merging gradually into
the uniformly rounded posterior margin, base gently convex, anterior end short and
rather narrowly rounded; outline distinctly concave between the anterior extremity
and the projecting umbones. Beaks incurved, umbones prominently rounded,
inconspicuous. A slight flattening of the surface between the umbonal ridge and

LAMELLIBRANCHIATA. 237

Cyrtodonta janesvillensis.]

the anterior basal margin. Surface nearly smooth in the young and middle stages
but with age one or more very strong marginal imbrications are developed. In
aged examples the anterior end is proportionally narrower than in younger ones.
Hinge plate of moderate length with a narrow ligamental area. Cardinal teeth
three in each valve, sub-horizontal, their inner ends thickened and curved down-
ward. Posterior teeth two in the left and three in the right valve. Both muscular
impressions faint. Shell rather thin.

All the Kentucky types of this species retain the shell and in the absence of
unquestionable casts of the interior for comparison with the Minnesota specimens
provisionally referred here, there may well be some doubt regarding the actual ex-
istence of the species within the borders of the state. The cast represented by fig.
30 exhibits certain peculiarities that it seems scarcely likely would occur in casts of
the Kentucky form. Thus the outline is less concave in front of the umbones and
the length of the shell less than it ought to be in a specimen of this size. The
original of figure 45, which is from the Trenton limestone at Cannon Falls, also
differs a little, but in this case oblique pressure has produced distortion that may
account for the differences.

This species is closely related to both C. huronensis and canadensis which Billings
described from the lower Trenton or Black River limestone of Lake Huron. Com-
pared with authentic specimens the first proves to be narrower posteriorly and the
second wider in front. In the latter the umbones are also more inflated. The
hinges of the two species as figured by Billings are also somewhat different.

Formation and locality.—The types of the species were found in the Birdseye and lower Trenton
limestone near High Bridge, Kentutky. The original of Figure 30 is from the middle third of the Trenton
shales at St. Anthony Park, St. Paul. That of Figure 45 from the Trenton limestone at Cannon Falls.

CyRTODONTA JANESVILLENSIS, 72. Sp.
PLATE XXXIX, FIGS. 26 and 27.

Comp. Cyrtodonta huronensis Billings, 1858, Can. Nat. and Geol., vol. iii, p. 482.

Shell of medium size, strongly convex, somewhat obliquely ovate, widest
posteriorly, the hight and length about as two is to three. Outline almost
uniformly rounded for an oval, with a slight prominence at the beaks and occasion-
ally at the posterior end of the hinge line. Anterior end very short. Beaks a little
compressed, rather small, incurved, projecting but little above the hinge. In casts
of the interior the umbonal ridge is strongly and the surface in front of it slightly
depressed. Anterior adductor scar, well defined, ovate, small, not more than half
the size of the posterior scar. The latter as usual is scarcely distinguishable.
Pallial line well marked, particularly in the basal and anterior parts. Hinge plate

5388 THE PALEONTOLOGY OF MINNESOTA.

(Oyrtodonta ampla.

of moderate strength; cardinal teeth three in each valve, sub-equal, curved and
rather oblique; posterior teeth slender, two or three in each valve. Surface of shell
with somewhat irregular concentric lines of growth. No trace of these are to be
seen in casts of the interior.

It is possible that the casts above described really belong to C. huronensis.
Although I have compared them with an authentic example of that species, labelled
by Billings himself as from the original locality for the species, I could not satisfy .
myself. The Wisconsin casts are certainly distinct from this specimen, having
smaller umbones and shorter anterior end, but the latter also does not agree with
Billings’ figures. Very likely the illustrations are not entirely trustworthy.

Compared with C. swbovata, the species is distinguished by its shorter, narrower,
and less distinct anterior end, comparatively greater length, less produced and more
oblique cardinal teeth, ard more distinct muscular and pallial impressions. That
species also attains greater size.

Formation and locality.—‘ Lower Blue beds” of the Trenton at Janesville and Beloit, Wisconsin.

Mus. Reg. No. 8323.

CYRTODONTA AMPLA, 7%. Sp.
PLATE XXXIX, FIG. 34.

In the outline this species resembles C. subovata and C. janesvillensis very closely.
It is known only from casts, but these are distinguished at once by the oblique ridge
running from the beak toward the posterior third of the base. On the anterior side
the surface descends sharply from the ridge into an unusually wide flattened space.
C. janesvillensis is also narrower anteriorly and relatively more convex. Another
species with which it is to be compared is the Galena form described by Meek and
Worthen as C. obliqua. The outline of that species is different being narrower in
front and more produced in the postero-hasal region, giving the shell a more erect
appearance. Its valves are also a little more convex. C. glabella is shorter. In the

associated forms of Vanuxemia the anterior adductor scar is much more sharply
defined.

Formation and locality.—Trenton limestone, Cannon Falls, Minnesota.

CYRTODONTA BILLINGSI, 2. Sp.
PLATE XL, FIGS. 2—6.
Cypricardites ventricosus Whitfield, 1882 Geol. Wis., vol. iv, p. 209, pl. 5, fig. 9.
Shell of medium size or less, transverse, obliquely ovate, highest in the posterior

half; valves strongly ventricose in the umbonal and central regions. Hinge line
at least two-thirds the length of the shell, slightly arcuate, posteriorly declining

LAMELLIBRANCHIATA. 539
Cyrtodonta biilingsi.]

and passing gradually into the broadly and uniformly curved posterior margin;
basal line most prominent and strongly convex behind the center, in front of which

~ point it ascends rather rapidly with a much more gentle curve into the short, small
and sharply rounded anterior end. Umbones full, large and prominent, beaks
small and strongly incurved; umbonal ridge subangular near the beaks only, incon-
spicuous in a lateral view. Surface marked with concentric lines of growth, These,
with the exception of a few near the margin, are obscure in the material at hand.
Ligamental area very narrow. Hinge plate of moderate strength, with three slightly
curved and nearly horizontal cardinal teeth and two or three slender posterior
lateral teeth in each valve. Pallial line and anterior adductor muscle distinct, the
latter rather small and of obovate or subcircular shape; posterior adductor faintly
impressed, situated immediately beneath the lateral teeth. Internal umbonal
sulcus and ridge slightly developed but always distinguishable on good casts of the
interior.

Although closely simulating several others this is still to be regarded as a well
marked species. Itmay be compared with C. huronensis Billings but will be found
to be higher, more erect and more ventricose. The umbones also are larger and
the cardinal teeth longer and more nearly horizontal. C. obliqua Meek and Worthen
has a straighter basal line and is more produced in the postero-ventral region. C.
glabellus and C. persimilis have a more rounded outline and smaller umbones. C.
subovata is longer, wider in front, not so ventricose, and has smaller umbones. A shell
that is likely to prove more troublesome to separate than any of these is the |’an-
uxemia decipiens. They are associated in the same strata at Minneapolis but when
good casts are available they may be distinguished at once by the higher position
and much greater sharpness of definition of the anterior muscular scar in the
Vanuxemia.

It is possible that the Wisconsin species referred by Whitfield to Cypricardites
ventricosus Hall, sp., in 1882 (loc, cit) is not identical with C. billingsi, because his
illustration, if correctly drawn, would indicate a distinct form. However that may
be it is quite certain that he had this species before him when he drew up his
description, since it is not uncommon at the localities mentioned by him. It is
certain also that neither the specimen figured by him nor the form now named
after Mr. E. Billings, the founder of the genus, are the same as the types of Hall’s
Edmondia ventricosa (Pal. N. Y., vol. i, p. 155; 1847). Indeed they are widely dis-
tinct species the last having proved to be a true Whitella and not Cypricardites nor
Cyrtodonta at all. On page 271, Pal. N. Y., vol. iii, Hall figures another species of
Cyrtodonta which he refers to his ventricosa as a Palwarca. This species is not the

same as C. billingsi being longer and having a well developed legamental area and

540 THE PALEONTOLOGY OF MINNESOTA.
[Cyrtodonta affinis.

different cardinal teeth. In all these respects the shell agrees much better with
an authentic example of C. carinata Billings, now before me, and as both the
Palwarca ventricosa of Hall and the Cyrtodonta subcarinata of Billings are from the
Trenton limestone in the northern part of Lake Huron, they are probably indentical.

Formation and locality.—Lower Trenton limestone Dunleith, Illinois; Beloit, Janesville and Mineral
Point, Wisconsin; Cannon Falls and Minneapolis, Minnesota.

CyrTopvonTa oBLIQUA Meek and Worthen.
PLATE XXXIX, FIGS. 35 and 36.

Cypricardites obliquus MEEK and WORTHEN, 1868, Geol. Sur. Il1., vol. iii, p. 311.

Of this species I have seen only the original type figured and described by
the authors. Their figures being unsatisfactory, it seemed worth the while to
prepare others, especially as the species may at any time be found within the
limits of the State. It is to be looked for in the middle and lower beds of the
Galena in Fillmore county. The type specimen is from the Galena at Scales
Mound, Illinois, and is now preserved in the Illinois State Museum.

CYRTODONTA AFFINIS, 2. sp.
PLATE XXXIX, FIGS. 20-23.

Shell small, rather compressed convex, obliquely subovate, alated and much
the highest posteriorly. Dorsal margin straight or very gently arcuate, rather long,
not passing gradually into the broadly and uniformly rounded posterior margin, the
junction being obtusely angular; ventral margin but little convex, ascending rapidly
to the small and narrowly rounded anterior end. Beaks small, projecting very little;
umbones compressed, due to a flattening of the antero-ventral slope; umbonal ridge
moderately distinct in the upper half; cardinal slope gently concave; greatest
thickness on the umbonal ridge above and a trifle in front of the center of the
valves. Surface with fine indistinct concentric striz and distinct sublamellose lines
of growth. Hinge of moderate thickness; cardinal teeth small, short, four in each
valve; posterior lateral teeth very slender, four in the right valve. Muscular im-
pressions rather faint, not well determined. Length 20 mm.; posterior (greatest)
hight 15 mm.; anterior highest 10 mm.; entire thickness 6.5 mm.

A variety reappears in the middle Galena. This is relatively more convex and
not quite as high posteriorly. Length 15 mm.; hight 10 mm.; thickness 7 mm.. It
may be distinguished as var. fillmorensis.

The typical form of this species is associated and was at first confounded with
Matheria rugosa. Aside from the hinge, which is of course very different in the two
forms, the Matheria is distinguished by its much shorter, subtruncate anterior end.

LAMELLIBRANCHIATA. 541

Crytodonta parva.]

Cyrtodonta halli Nettleroth, sp., from the upper beds of the Hudson river group of
Kentucky, is shorter and thicker, and has more prominent beaks and umbonal
ridge.

Formation and locality —The typical form occurs in the upper part of the middle third of the Tren-

ton shales, six miles south of Cannon Falls, Minnesota. The Galena variety was collected near Wykoff,
in Fillmore county.

CYRTODONTA, PARVA, ”. Sp.
PLATE XXXIX, FIGS. 24 and 25.

This small species seems to be closely related to C. affinis Ulrich and C, halli
Nettleroth, sp. In some respects it is intermediate between those species, differing
from the first in its greater convexity, stronger umbonal ridge and larger anterior end,
these being points in which the shell agrees rather closely with the latter. From both
it differs in the more abruptly rounded postero-basal margin and straighter ventral
outline.

Adductor scars very faint, undetermined. The specimen being a cast of the
interior, the detail of the hingement could not be made out with certainty.

Greatest length, 9.5 mm.; greatest hight, 6.5 mm.; thickness, 4.5 mm.

Formation and locality—Middle Galena, near Fountain, Minnesota.

CYRTODONTA ROTULATA, 2. Sp.

PLATE XXXIX, FIGS. 16—19.

Shell small, moderately ventricose, nearly erect, the outline uniformly rounded
(subcircular) except at the dorsal margin, which is straight behind the beaks and
somewhat insinuated in front of them; hight and length about as five is to six;
posterior extremity of hinge angular. Beaks small, incurved, scarcely prominent,
situated about one-fourth of the length of the shell behind the most prominent point
on the anterior margin. Umbonal region full, but not excessively so; point of
greatest convexity a little above and in front of the center of the valves; postero
cardinal slope gently concave, causing this part of the shell to appear as slightly
alate. Surface marked with fine concentric lines, with a few (those shown in the
illustrations) stronger than the rest. Shell and hinge plate thin; dentition undeter-
mined beyond this that it is essentially as called for by the genus. Muscular scars
unknown.

Iam not acquainted with any species of Cyrtodonta, described heretofore, with
which this one might be confounded. C. persimilis Ulrich, a much larger species, is
in outline somewhat like it, but on comparison proves to have the beaks situated
farther forward and to be proportionally less ventricose. Several species belonging

542 THE PALEONTOLOGY OF MINNESOTA.

[Cyrtodonta obesa.

to the genus Vanuxemia agree even more closely in their outlines, but in all of them
the shell is much thicker and the hinge generically different. Of all known species
the two next described are to be considered as the nearest.

Formation and locality.—The real types of the species were obtained from Mercer county, Ken-
tucky, where they were found in a cherty bed equivalent to the Black River limestone of New York.
Two specimens, both a little larger than the Kentucky types, were collected in Minnesota. Both are
from the middle third of the Trenton shales, one at Minneapolis, the other near Fountain.

Mus. Reg. No. 8336.

CyRTODONTA OBESA, ”. Sp.

PLATE XXXIX, FIGS, 10, 11 and 12.

This species is, so far as our knowledge extends, very closely allied to C. rotulata.
It is also associated with it in both Kentucky and Minnesota, but I cannot say that I
experienced much trouble in separating them. C. obesa is more gibbous and oblique,
the anterior end is shorter and much more obtuse in a cardinal view, the posterior
cardinal slope narrower and scarcely to be described as alate, while the outline at
this extremity of the hinge is more rounded; the entire outline is to be called
broadly ovate rather than subcircular. The umbones also are more prominent and
inflated.

Length, 14 mm.; from beak to posterior extremity, 14 mm.; hight at center of
shell, 11.; thickness, 10.5 mm. In another specimen these dimensions are respectively
14.2, 14, 11 and 10 mm.

The above measurements are furnished by two silicified examples from Kentucky,
which are to be regarded as the types of the species. Besides these two evidently
young shells from Minnesota localities are referred here provisionally. They are
too oblique for C. rotulata and have not the proper shape for C. cingulata. The out-
line is very nearly as in C. obesa, but they differ from the Kentucky specimens in
being less gibbous, especially in the umbonal region.

Formation and locality —In cherty beds equivalent to the Black River limestone of New York, in
Mercer county, Kentucky. Specimens doubtfully referred to the species were found in the middle third
of the Trenton shales at St. Paul and Preston. Minnesota,

CYRTODONTA GIBBERA, 2. Sp.

PLATE XXXIX, FIGS. 13—15.

In this specimen the umbones are more inflated even than in C. obesa. They
are also situated farther forward, the anterior end being very short and exceedingly
obtuse. Although the posterior extremity is subangular, the form on the whole is
more rotund, the hight of the shell being greater. C. rotulata is much less gibbous
in the umbonal and central regions, less oblique and a little longer, particularly in

eo

LAMELLIBRANCHIATA. 54

Cyrtodonta glabella.

the part that is in front of the beaks. Several species of Vanuxemia present a similar
external appearance, but they have all a thicker shell and are quite different intern-
ally, so that casts of the interior could not possibly be confounded.

Length, 14.2 mm.; from umbone to postero-basal margin, 14.8 mm.; hight at
middle of shell, 13 mm.; thickness, 11 mm.

Formation and locality.—Base of the middle Galena, about thirteen miles south of Cannon Falls,
Minnesota.

CyRTODONTA GLABELLA Ulrich.
PLATE XXXIX, FIGS. 37 and 40.

Cypricardites glabella ULRICH, March, 1892, Nineteenth Ann. Rep. Geol. and Nat. Hist. Sur. Minn.,

Cypricardites minnesotensis enna April. 1892. Bull. Minn. Acad. Nat. Sci., vol. iii, p. 338.

Shell of medium size, moderately convex; broad ovate or subquadrangular in
outline, with the back straight and rather long, the posterior margin broadly rounded,
sometimes nearly vertical and slightly straightened in the middle, above making
an obtusely angular or more or less rounded junction with the hinge line; ventral
and anterior margins rounded, the latter turning rather sharply backward at the
hinge. Beaks situated well forward, small, very slightly prominent, the umbonal
region full, with the line of greatest convexity—not sufficiently defined to be called
a ridge—extending obliquely across the valve from the beaks. Cardinal slope flat,
rather abrupt; between this and the undefined umbonal ridge, the surface is again
flattened; anterior and basal slopes gently convex. Surface marked with somewhat
irregular concentric lines of growth.

Good moulds of the interior show that the hinge plate was strong, the liga-
mental area very narrow, the cardinal teeth at least two and strong, and the poster-
ior teeth two or three iw each valve. The beaks are prominent, incurved, and com-
pressed because of a sulcus that crosses the valves a little obliquely, but is lost before
reaching one-half the distance to the ventral border. On each side of the suleus is a
very faint ridge. Anterior adductor distinct, rather small, ovate, acuminate below.
Pallialline distinct, especially the anterior part where it appears as a sharply
defined pustulose ridge in the cast. Posterior adductor ovate, the long diameter
vertical, nearly three times the size of the anterior, situated about one-third of its
length beneath the posterior end of the hinge plate.

This fine shell is an early form of the group of species of which C. germana,
C. grandis and C., billingsi are more typical representatives. It is distinguished
from them all by the more anterior position of the beaks, and greater prominence
of the antero-basal margin. The next species, though very similar in most respects,
belongs to another group of species, in which the internal ridge and sulcus is
indistinguishable.

544 THE PALEONTOLOGY OF MINNESOTA.

(Cyrtodonta pesrsimilis.

Formation and locality.—The original type is from the middle third of the Trenton shales at Minne-
apolis. A small cast of the interior, belonging to the survey collection, was found in the building lime-
stone at the same place. Casts occur also in the lower Trenton limestone at Beloit, Wisconsin and Dun-
leith, Dlinois.

Mus. Reg. No. 5100.

CYRTODONTA PERSIMILIS, 1. Sp.

PLATE XXXIX, FIGS. 41 and 44.

This form, which is known only from casts of the interior, was confused with
C. glabella until a critical comparison proved it to be not only distinct but to belong
to another group of species. The outline is very much alike in the two species, but
here even some constant differences are to be observed, especially in the shape of
the margin at the posterior extremity of the hinge, where the present species is
more angular. But the main difference lies in the fullness of the umbones, there
being no appreciable sign of the sulcus and ridge which cross this portion of casts
of that species. This difference is very obvious after it has once been pointed out.
The beaks are also more strongly incurved and the hinge bent downward anteriorly
in a greater degree, while the plate is probably also of less width. Finally, the
posterior muscular scar is closer to the hinge and the longer diameter of the
impressions more oblique.

The systematic position of the species is near C. rotulata, C. cingulata, and C.
tenella. The first is more rotund in outline, less oblique and has fuller umbones,
the others are higher and have the beaks situated farther behind the anterior
extremity.

At Minneapolis C. persimilis is associated with a small Vanuxemia that is not
easily distinguished unless the casts are clean and in good condition. The latter
(V. decipiens,)differs somewhat in its outline being proportionally narrower anteriorly,
but the principal difference hes in the character of the anterior adductor scar, which
is much more distinct from the umbonal cavity. In short, the species is not a
Crytodonta but a Vanuxemia as now defined.

Formation and Locality.—Trenton limestones, Minneapolis, Minnesota, ‘“‘ Lower Blue Beds” of the
Trenton formation at Beloit, Wisconsin. :

Cyrtoponta ovirormis, Ulrich.
PLATE XXXIX, FIG. 16; PLATE XL, FIG. 1.
Cypricardites oviformis ULRICH, 1892. Amer. Geol.,’vol. x, p. 99.
Shell rather above the medium in size, moderately convex, but little oblique, the
outline almost regularly oval, with the posterior end a little the widest and a slight

straightening along the cardinal margin. Beaks small, situated between one-fourth
and one-fifth of the length behind the anterior extremity; erect, compressed and not

LAMELLIBRANCHIATA. 545

Cyrtodonta cingulata.]

incurved in casts of the interior; in the shell projecting very little above the hinge
line. Umbonal ridge very indistinct, with the point of greatest convexity a little
above and in front of the middle. In the casts there is a more or less sharply defined
and unusually wide depressed or Hattened strip running from the beaks downward.
Hinge plate wide and strong, with two strong posterior lateral teeth in each valve,
and sometimes a third small oné above them in the left valve. Anterior teeth con-
sisting of one long tooth placed parallel with the margin of the shell in front of the
beaks and five or six small unequal teeth running downward from the horizontal
tooth. Ligamental area well developed. Anterior muscular scar distinct, elongate,
vertically disposed, situated immediately beneath the cardinal teeth. Posterior scar
illy defined. Shell substance thin, except in the anterior and dorsal region.

The small vertically arranged anterior teeth, and the erect and strongly com-
pressed beaks of casts of the interior are the two principal peculiarities of the
species. These and other equally obvious characters distinguish it from C. glabella
Ulrich. C. saffordi Hall, sp., often has the cardinal teeth broken up in a similar
manner, but differs too obviously in other respects to render confusion between
them at all likely.

Formation and locality.—Two opposite valves were collected by Mr. Chas. Schuchert at Janesville.
Wisconsin, in the “Lower Blue limestone.” These are now in the museum of the Geological and Natural
History Survey of Minnesota. .

Mus. Reg. No. 8324.

Cyrroponta CrncuLata Ulrich.
PLATE XL, FIGS. 7 and 8.

Cypricardites cingulata ULRICH, 1892. Nineteenth Ann. Rep., Geol. and Nat. Hist. Sur. Minn., p. 235.

Shell scarcely reaching the medium size, ventricose in the central and umbonal
region, oblique, narrow anteriorly and broadly rounded posteriorly; the outline on
the whole, excepting a slight prominence at the postero-cardinal edge, almost regu-
larly ovate; hinge line rather short posterior to the beaks, slightly convex. Beaks
of good size, strongly incurved, projecting well above the hinge, situated a little
more than one-fourth of the entire length behind the anterior extremity; umbones
prominent, full, with an obtuse ridge or line of greatest altitude running from the
beaks towards the postero-basal side; anterior and cardinal slopes both slightly
concave, the latter descending more rapidly. Point of greatest convexity near the
middle of a line drawn parallel with and one third of the hight of the shell beneath
the hinge. Surface marked with very fine concentric lines, easily abraded, and
distant irregular lines or wrinkles of growth, Shell substance thin, Internal char-

acters unknown.
—35

546 THE PALEONTOLOGY OF MINNESOTA.
[Cyrtodonta tenella.

This species seems to be rather closely related to Cyrtodonta canadensis Billings,
but is more erect, comparatively higher posteriorly and has its outline more pro-
duced and more sharply rounded in the postero-cardinal region. C. tenella has a
longer hinge line and is more uniformly convex. C. grandis Ulrich, is a larger and
almost circular shell. .

Although the hingeand internal characters are unknown, I cannot doubt that
the species isa true Cyrtodonta. I judge further that it belongs to the group of species
of which C. persimilis and C. rotulata are typical members,

Formation and locality.—Middle third of the Trenton shales, Minneapolis, Minnesota.

CyRTODONTA TENELLA Ulrich.
PLATE XL. FIGS. 15-19.

Cypricardites tenellus ULRICH, 1892. Nineteenth Ann. Rep. Geol. and Nat. Hist. Sur. Minn., p. 287.
:

Shell of medium size or less, moderately ventricose, not very oblique, subovate,
widest posteriorly, slightly alate and subangular or sharply rounded in the postero-
cardinal region. Hinge line long, slightly arcuate, posterior margin straightened
in the upper half, broadly rounded and produced a little in the lower half; ventral
margin rather strongly convex, most prominent a little behind the middle; anterior
end more or less narrowly rounded. Beaks small, incurved, projecting moderately
beyond the hinge line; situated about one-fourth of the entire length behind the
anterior extremity; umbones full, prominently rounded. Cardinal slope slightly
concave. Surface marked with rather fine concentric striew, and sometimes with
strong distant lines of growth as well.

Shell substance very thin. Hinge plate narrow, a good part of it forming a finely
striated ligamental area; two very slender posterior lateral teeth in the right valve,
and the same number probably in the left; anterior teeth obscure in the specimen,
consisting apparently of two slight horizontal folds in the margin of the shell,
muscular impressions very faint. '

The hinge plate and teeth are thinner in this species than in any other known
from Lower Silurian deposits. In two Upper Silurian species, however, C. primigenia
Conrad, sp. (Medina), and C. dictwa Hall, sp. (Niagara), the hinge is quite as slender
if not more so.

C. cingulata is a more ventricose shell, especially in the central and umbonal
regions; the outline is a little different, being longer from the beaks to the postero-
ventral margin, and the hinge line shorter. C. grandis and its varieties germana and
luculenta, the first and second from the Galena, the last from the Hudson River
group, are very similar shells, differing chiefly in the greater strength of their hinges.

LAMELLIBRANCHIATA. 547
Cyrtodonta grandis.]

Casts of what may be a small variety of C. tenella occur in the Trenton limestone
at Minneapolis. The largest seen (Mus. Reg. No. 700), is only 12 mm. long. Aside
from the matter of size, they agree very well indeed with the types of the species.

Formation and locality.—Upper part of middle third of the Trenton shales, about six miles south of
Cannon Falls, Minnesota.

Mus. Reg. No. 8336.
CyrtoponTa GRANDIS Ulrich; and varieties.

PLATE XL, PIGS. 9-14.

Cypricardites grandis ULRICH, 1890. Amer. Geol., vol. vi, p. 387.
Cypricardites germanus ULRICH, 1892. Nineteenth Ann. Rep. Geol. and Nat. Hist. Sur. Minn., p. 236,
Cypricardites luculentus SARDESON, 1892. Bull. Minn. Acad. Nat. Sci., vol. iii, p. 338.

‘

Fig. 43. Cyrtodonta grandis, and varieties. a and b, anterior and lateral views of@a perfect speci-
men, upper Trenton, two miles south of Burgin, Kentucky. e¢ and d, lateral and antero-cardinal views
of a small left valve of same, with stronger Surface markings than usual; from same formation and
locality. e, nearly entire cast of the interior of a left valve, from same locality. /f, Small fragment of
a cast of the interior of a left valve, preserving sharp impressions of the anterior adductor scar and
cardinal teeth. g, the cardinal part of a cast of the interior of a right valve, drawn without the beak
so as to show the entire hinge. i, hinge of specimen shown in figure ce and d. j, original type of C.
germana, restored; hinge of same figured on plate xu. k, interior of two left valves of C. grandis var,

intermedia, n. var.; Trenton, Haynie’s Mill, Tennessee.
——

548 THE PALEONTOLOGY OF MINNESOTA. Hes
[Oyrtodonta grandis.

Shell large, moderately ventricose, slightly oblique, the outline subcircular.
Beaks small, projecting slightly above the hinge line, obliquely incurved, almost in
contact; situated about in the middle of the anterior half of the cardinal margin.
Umbonal ridge inconspicuous, the slope of the surface to the postero-cardinal mar-
gin gradual and slightly concave, the slope to the basal and anterior margins very -
gently convex; point of greatest convexity a little above the center of the shell. An-
terior end longer in front of the beaks than usual in this genus, the margin narrowly
rounded above, then with a very gentle and almost uniform downward and backward
curve, merging imperceptibly into the basal, and later into the posterior margin.
Antero-cardinal edge slightly produced; likewise the postero-ventral, but in most
cases so gently as to be scarcely appreciable. Surface smooth, with fine concentric _
lines of growth.

- Ligamental area deep but appearing narrow in a cardinal view. As usual, it is
finely striated longitudinally. Hinge plate strong, with three anterior teeth in the
left, and four in the right valve. These teeth are short and abruptly curved down at
their posterior ends, terminating with a knob-like projection. In the right valve
the first and fourth are much smaller than the second and third; the middle tooth of
the three in the left valve is also much the largest. Posterior teeth longer, parallel,
and slightly curved, three in the right valve and two in the left. Anterior and pos-
terior muscular scars large, situated just beneath the two sets of hinge teeth, the
posterior one rather faintly impressed, the anterior deep. Pallial line simple, only
the anterior half sharply defined, and often emphasized by a series of small pits.
Inner side of shell with two low, subparallel ridges extending from the beaks two-
thirds the distance to the postero-basal margin. The furrow between these appears
as a low ridge on casts of the interior. These often present another but much
smaller ridge running downward from the inner margin of the anterior muscular
scar. In casts the beaks are flattened, very prominent, not strongly incurved nor
far apart.

The above description does very well for the large Kentucky types upon which
‘the species was founded. It is also wide enough to include a few of the numerous
casts that occur in the lower and middle beds of the Galena of Minnesota. The
majority of them, however, seem to fall more nearly under the variety or species
germana whigh was established (Joc. cit) for the reception of usually smaller specimens
in which the form is a little more oblique and-the hinge plate proportionately thin-
ner and longer, with the cardinal teeth less curved and the posterior teeth placed
more nearly horizontal. The internal furrow and the anterior muscular scar, are
both less deep in this variety, than in the true grandis, The same is true of the
pallial line. |

LAMELLIBRANCHIATA. 549

Vanuxemia.]

Fig. 9 of plate XL, represents what appears to be a large right valve of germana.
The specimen is preserved as a partial mould of the exterior. Another specimen
from the Galena near Wykoff may be said to be identical in its characters with the
original types of germana. The specimen represented by fig. 10 is one of a number
in which the balance of agreements is with the variety rather than with typical
grandis, while the original of fig. 11 was made by a small right valve of which the
opposite seems to be true.

Another variety was found in the Trenton of Tennessee by Prof. Jas. M. Safford,
and sent to me for examination. The illustrations show that in its outline and
general appearance this new variety closely simulates variety germana and C. tenella.
It differs, however, in the teeth which are stronger and more curved than in those
forms, being on the whole more like those of C. grandis and C, saffordi. As it marks
another stage in the development of this type of shells it should receive aname. I
propose therefore that it be called Cyrtodonta grandis, var. intermedia.

Mr. Sardeson has given the name /uculenta (loc. cit.) to a Hudson River form of
which the hinge and exterior of two fair examples are represented on Plate XL, by.
figs. 13 and 14. This form I cannot now regard as specifically distinct from C. grandis,
since it is almost identical with var. germana, the only difference being small ones
in the hinge and that the umbones are somewhat larger in the /uculenta.

Two other stages in the development of this series of shells, in these cases per-
haps of specific importance, occur in the upper beds of the Cincinnati group at Rich-
mond, Indiana. These I hope to describe in another publication.

°

Formation and locality.—The types of C. grandis and the var. germana, are from the upper Trenton
between Burgin and Danville, Kentucky. Casts of the species and variety have been found im the middle
and lower Galena near Cannon Falls, Kenyon, Pleasant Grove, Wykoff, Lime City, and other localities in
Minnesota; at Decorah, Iowa,-and Oshkosh, Wisconsin. The variety intermedia is so far known only
from the Trenton at Haynie’s mill, in Tennessee, where it occurs in association with Vanuxemia hayniana
Safford, sp. The var. luculenta occurs in the shaly limestones of toe Hudson River group at Granger and
other localities in Fillmore county, Minnesota.

Mus. Reg. Nos. 8337, 8347, 4102, 8360, 8333. -Var. luculenta 8332.

Genus VANUXEMIA, Billings.

Vanuxemia, BILLINGS, 1858. Rep. of Progr. Geol. Sur. Can., p. 186.

Shells ventricose, oblique, acuminate ovate to subcireular; anterior end very short
and small, the posterior broadly rounded. Umbones full, prominent, beaks strongly
incurved. Surface with concentric growth lines only. Hinge strong, with teeth
as in Cyrtodonta, two to four, rarely more, cardinal, and two to four posterior lateral
teeth in each valve. Teeth frequently striated transversely, an elongated ligamental
area generally present. Two adductors, the anterior depression very sharply defined
and deep, and situated in a prolongation from the anterior end of the hinge plate;

550 THE PALEONTOLOGY OF MINNESOTA.

{Vanuxemia dixonensis.

in casts of the interior forming a distinct lobe-like prominence, often of reniform
shape, immediately in front and sometimes partly between the filling of the beaks.
Posterior scar indistinct, larger than the anterior. Pallial line simple. Internal
umbonal ridge well developed.

Type: Vanuxemia inconstans Billings.

As a rule this genus can be distinguished from Cyrtodonta by ‘the more nearly
terminal position and greater prominence of the beaks, but the final and only reliable
test lies in the position and character of the anterior adductor sear. This, in being
excavated out of the hinge plate instead of being placed on the floor of the valve,
makes so obvious a difference that I cannot see, now that it is pointed out, how any
one can fail to discriminate between the two genera.

Between twenty and twenty-five valid species of Vanuxemia are known to me.
They are all Lower Silurian and, although Billings has placed a Devonian shell here,
Iam almost satisfied that the genus became extinct with the close of the Hudson
River deposits.

VANUXEMIA DIxoNENSIS Meek and Worthen.
PLATE«XXXVIII, FIGS. 1—5.

Vanuxemia dixonensis MEEK AND WORTHEN. Pro. Chicago Acad. Sci., vol. i, p. 16; also 1868, Geol.
Sur. Ill., vol. iii, p. 297, pl. 1, fig. 5a, b.

Shell beneath medium size, very gibbous, obliquely acuminate-ovate, the nar-
rowly rounded rostrum forming the small end of the oval. Outline gently arcuate
dorsally, and usually rather sharply rounded at the posterior extremity of the hinge;
from this point around the lower half of the shell, the outline sometimes forms a
regular semicircle, but it is more common to find that the center of the base is more
or less produced. (See fig. 4.) Anterior end rounded, projecting very little, if at all,
beyond the nearly terminal beaks. Beneath the latter the outline is insinuated
often strongly, but in most cases more gently than in fig. 5; in a front view an unde-
fined heart-shaped lunule-like depression. Umbones tumid and prominent, with the
beaks curving strongly inward and forward. An obtuse curving ridge extends from
each beak backward along the depressed hinge line.* These dorsal ridges form a
broad flattened or rather concave back to the closed valves. Just within them an
impressed line, defining a lanceolate escutcheon-like area, is sometimes distinguish-
able. Surface marked with strong, but unequal concentric lines of growth.

In casts of the interior the beaks stand far apart (much more so than in the
shell), are very prominent, broad, much compressed, concave on the inner side, sharp-
edged in front and very little incurved, while a more or less strong and nearly vertical
sulcus and ridge marks the anterior half. The dorsal ridges are sharper than on the

or
Or
—_

LAMELLIBRANCHIATA,

Vanuxemia dixonensis, var. insueta.]

shell itself, and a flattening of the surface beneath them is usually distinguishable.
Anterior muscular impression distinct, reniform, the pair forming a strongly defined
lobe at the base of the beaks. Posterior scar large, but very faint. Pallial line
rather indistinct, except in the anterior part. ‘

Shell substance very thick in the anterior third. Ligamental area with good

definition, strongly concave, long, high, but not wide in a dorsal view. Posterior
lateral teeth, three in each valve, the upper often much the smallest; in many cases
more nearly horizontal than shown in fig. 4. Cardinal teeth normally three in each
valve, subequal, nearly horizontal, slightly curved. Occasionally the upper one is
more slender than usual, and one or both of the others divided so that their number
may be four or even five in each side.
' This species, which is one of the most abundant and best marked fossils of this
class found in Minnesota, was at first believed to be identical with V. inconstans Billings,
but a second comparison with the original description and figure of that spocies
seemed to throw some doubt upon their identity. This doubt was strengthened to
conviction when a few days ago I received from Prof. Jas. M. Safford an authentic
example of Billing’s species. This shows that, despite the close agreement of the
two species, Meek and Worthen were fully justified in separating theirshell. The
principal difference lies in the anterior part of the shells, which in V. inconstans is
more obtuse than in V. dixonensis, and in the upper part just beneath the beaks pre-
sents a small protuberance where the latter has a lunule-like excavation. This
difference is due to the shape of the anterior extremity of the hinge, this being
angular in V. inconstans and well rounded in V. dixonensis.

Compared with other species, V. rétundata Hall, sp., and V. suberecta, and V. crassa
are all less oblique and of rounder outline; in V’. obtusifrons the dorsal outline is
concave instead of convex.

Formation and locality.x—Very common in the upper beds of the Trenton Ilmestone at Minneapolis
and St. Paul; less abundant at Cannon Falls and other localities in the state. In the ‘t Lower Blue beds”
at Janesville, Wisconsin, and Dixon, Illinois. .

Mus. Reg. Nos. 202, 320, 670, 5080, 5098, 5525, 5527, 5876, 8322, 8330, 8881.

VANUXEMIA DIXONENSIS, ‘Var. INSUETA, ”. var.
PLATE XXXVIII, FIGS. 6 and 7,

This name is proposed provisionally for one or two casts differing from the
ordinary form of V. dixonensis apparently in one important respect only, namely,
the sulcus and ridge which should traverse the anterior part of the cast from the
umbones downward is wanting except above the anterior muscular scar where a
slight flattening of the umbones may represent the sulcus. The beak also is more
incurved than in any specimen of the typical form of the species seen.

Or’
On
DOU

THE PALEONTOLOGY OF MINNESOTA.

[Vanuxemia rotundata.

Formation and locality._Upper part of the Trenton limestone, Minneapolis, Minnesota. The
illustrated specimen.was found by Mr. A. D. Meeds and kindly given by him to the author. The other,
a much smaller and doubtful cast, belongs to the survey collection and bears the museum register
number 8329,

@ VANUXEMIA ROTUNDATA Hall.
PLATE XXXVIII, FIGS. 8—14.

Cypricardites rotundata HALL, 1861. Rept. -Supt. Geol. Sur., Wis. p. 29; 1862, Geol. Rept. Wis.,
vol. i, p. 38, fig. 7, and p. 4387.

Cypricardites rotundatus (part.) WHITFIELD, 1874. Geol. Rept. Wis., vol. iv, p. 208. (Not the speci-
men illustrated—pl. V, fig. 11—which belongs to V. subereeta ULRICH.)

This species is very similar to V. dixonensis Meek and Worthen, and a another
direction quite as much like V. suberecta Ulrich. Still, as it is very constant in its
peculiarities, and not at all difficult to distinguish, it should be recognized as a dis-
tinct species. From the first it differs in being shorter from the beaks to the base
and therefore circular rather than ovate in outline. The form of the casts, the only
condition in which the species has been observed, is more erect, the beaks curving
much less forward so that the anterior margin projects considerably beyond them.
The anterior sulcus is on the whole stronger, the pallial line more distinct, and the
average size of the shells little more than half what it is in V. dizonensis. In other
respects, including the hinge, the two species are practically indentical. Hall says
there are two posterior lateral teeth in each valve, and Whitfield one or two, but in
all the specimens seen by me (about fifty), their number was not less than two and
oftener three.

Compared with V. suberecta, a form that was united by Whitfield with V. rotwn-
data, the latter is found to be more oblique, with the anterior end longer and more
rounded above, the sulcus stronger, more curved, narrower, and without the small
ridge which is included in the sulcus in that species. Nor is the anterior boundary
of the sulcus, especially beneath the muscular scar, so much thickened. There are
furthermore some differences in the backs of the two species, the hinge line being
less sunken, the dorsal ridges more obtuse, and the outline, in a side view, straighter
and even a little concave behind the beaks in some casts of V. suberecta. The hinge
of the latter is not fully known, but so far as our knowledge goes, it adds another
difference in the greater obliquity of the cardinal teeth. The survey colléction con-
tains two examples (Mus. Reg. No. 8321) of an unusually convex small variety of this
species. Four views are given of one of these on plate xxxvu.

Formation and locality—Very common in the ‘Lower Blue Beds” of the Trenton formation at
Janesville and Beloit, Wisconsin. A few specimens from the upper part of the limestone at Minneapolis,
are doubtfully referred here.

Mus, Reg.’ Nos. 25101, 8319, 8321.

~

LAMELLIBRANCHIATA. 553

Vanuxemia suberecta. |

VANUXEMIA SUBERECTA, 2. Sp.
PLATE XXXVIII, FIGS. 20—22.

Cypricardites rotundatus (part.) WHITFIELD, 1874. Rept. Geol. Sur. Wis., vol. iv, p. 208, pl. V. fig. 11.

Casts of the interior subcircular, strongly convex, suberect, with strong erect and
scarcely incurved beaks situated nearly one-fourth of the length of the shell behind
the anterior extremity. Back (without hinge) nearly straight; flattened sulcus wide,
distinct, yet not deep; vertical], causing a marked compression of the anterior part of
the umbones; usually includes one or two obscure vertical ridges. Hinge plate
strong, with several (?3 or 4) strongly oblique cardinal and three posterior lateral
teeth in each valve. :

There is no doubt in my mind respecting the specific distinctness of this shell
and the smaller and much more abundant V.votundata. As I have already pointed
out the difference, I shall not repeat them, but will refer the reader to the remarks
on that species. The next species V. media, though very similar in its general expres-
sion, is not I believe so closely related. The beaks are smaller and more incurved,
and there is a decided concavity in the dorsal outline behind the beaks, while the
anterior margin has a slight backward direction that is not seen in V’. swberecta.

Formation and locality.—Upper Buff limestone of the Trenton formation at Beloit, Wisconsin.
Mus. Reg. No. 8328.

VANUXEMIA MEDIA, M. Sp.
PLATE XXXVIII, FIGS. 23—26.

Shell small, strongly convex, rounded, a little the highest posteriorly; anterior
margin slightly oblique, dorsa] outline distinctly concave behind the beaks. Umbones
of moderate size and prominence, but little compressed, beaks incurved. Hinge plate
of moderate strength, the details of its structure not well determined. Anterior
muscular scar rather small, and not so strongly defined as usual for the genus. Pal-
lial line indistinct except for a short distance beneath the anterior muscle.

This species, though smaller, seems to be intermediate in its character between
V. suberecta Ulrich and V. hayiana Safford, sp. It is of more rounded form and has
larger and more prominent umbones than the latter, while in these same features it
fails to equal the fornfer. The anterior muscular scar is smaller and unusuaily
shallow. Other differences may be noticed but those mentioned will, it is believed,
suffice for the recognition of the species.

Formation and locality.—Trenton limestone, Minneapolis and Cannon Falls, Minnesota.

VANUXEMIA CRASSA, ”. Sp.
PLATE XXXVIII, FIG. 27.
This species, seems, on the whole, to have been much like V’. suberecta, but is
readily distinguished by the remarkable strength of its hinge and the great internal

554 THE PALEONTOLOGY OF MINNESOTA.

[Vanuxemia obtusifrons.

thickening of its shell in the umbonal and anterior parts. The beak is compressed
in the cast, very prominent and not at all incurved; the anterior muscular scar
strongly defined, large, of subcircular form with the inner side truncated; the pallial
line is distinguishable all around and, for some distance beneath the anterior muscle,
strongly defined by a deep and unusually wide furrow, out of which the anterior
side of the body of the cast rises very abruptly. Ligamental area high and strongly
striated longitudinally; cardinal teeth strong, comparatively Jong and _ slightly
curved, three in number; posterior lateral teeth three, strong and a trifle more
oblique than the cardinal teeth. Dorsum of cast broad and flat.

The external characters of the shell are unknown, but as the species doubtless
_ belougs to the most typical section of the genus, they will probably prove ntuch as

in V. inconstans, V. dixonensis and V. rotundata.

Formation and locality.—Middle third of the Trenton shales, St. Paul, Minnesota.

VANUXEMIA oBTUsIFRONS Ulyich.
PLATE XXXVIII, FIGS. 15-19.

Cypricardites obtusifrons ULRICH, March 3, 1892. Nineteenth Ann. Rep., Geol. and Nat. Hist. Sur.

Cypricardites vicinus See eae Bull. Minn. Acad. Nat. Sci., vol. iii, p. 339.

Shell rather large, moderately ventricose, very oblique, subovate, much the
highest and broadly rounded posteriorly, with the beaks subterminal, incurved, not
very prominent nor large, and the umbones strongly rounded. Anterior end obtuse,
the upper part forming nearly a right angle with the hinge line, the slightly project-
ing junction between the two lines rather sharply rounded; postero-basal half of shell
broadly semielliptical; dorsal outline very gently concave. Surface markings con-
sisting of irregular, fine and coarse, sublamellose lines of growth.

Casts of the interior with the beaks large, very prominent, compressed and
strongly incurved at their apices; umbonal ridge and sulcus of moderate definition,
nearly parallel with the anterior margin. Anterior muscular sear large and strongly
defined, excavated out of the hinge plate, in the cast having the appearance of a strong
process projecting from the under side of the base of the beak forward and upward
to the anterior extremity of the hinge; posterior scar illy defined, large, ovate, situ-
ated close to the posterior end of the hinge. Pallial line distinct.

Hinge with three cardinal and three posterior lateral teeth in each valve, both
sets strong. The cardinal teeth are situated under the beaks, finely toothed on
their sides, sightly curved and usually oblique, ranging at an angle of 45° or more

with the hinge line.*

*The original figure of the interior of this species is faulty in its representation of the cardinal teeth. The type
specimen has been injured at this point and in such a manner that I quite overlooked the actual remains of the teeth

LAMELLIBRANCHIATA. 555

Vanuxemia sardesoni.]

The species may be compared with V. inconstans Billings, V’. niota Hall, sp., V.
hayniana Safford, sp., V. sardeson and V. umbonata. None of these forms, however,
seem to me sufliciently similar to render the separation of the present species
troublesome,

Formation and locality.—Blue limestone of the Trenton at Minneapolis, Minnesota.
Mus. Reg. No. 5524. :

VANUXEMIA SARDESONI Ulrich.
S PLATE XXXVII, FIGS. 17—19, and PLATE XXXVIII, FIG. 45.

Cypricardites sardesoni, ULRICH, 1892. Nineteenth Ann. Rep. Geol. and Nat. Hist. Sur. Minn., p. 231.

Shell a little above the medium size, known only from casts of the interior, and
the impression of the hinge and free margins on the limestone matrix. The outline
was subrhomboidal, with the cardinal and anterior margins nearly straight, and the
two lines forming an angle of about 62°; anterior extremity subacuate or sharply
rounded, hinge line equaling nearly three-fourths of the entire length, postero-ventral
margin broadly rounded, almost semicircular; above this the posterior outline is some-
what straightened and slopes forward rapidly, meeting with the cardinal line to form
an angle of about 135°; the immediate junction however is not perceptibly angular.

In the casts the beaks project strongly, are nearly terminal, pointed, slightly
incurved, greatly compressed, and somewhat twisted. A strong sulcus extends from
the beaks to the postero-basal part of the casts; this sulcus occupies the larger part
of the anterior slope, and from its inner side the umbonal ridge, constituting the
highest portion of the surface, rises abruptly.. For the reasons mentioned the
anterior slope appears flattened and in part concave, while the posterior is almost
uniformly convex to the margin. Cardinal slope abrupt, especially near the hinge.

Gutta-percha impressions bring out the internal characters in a very satisfactory
manner. They show a wide and faintly striated ligamental area, two lateral and
two cardinal teeth, both pairs large and distinctly crenulated on the sides. The

cardinal pair are considerably curved and the lower one forms the upper boundary

of the very sharply impressed anterior muscular scar. On the whole the hinge
- impresses one as being unusually strong. The posterior muscular scar is large,
ovate, slightly prolonged below and but faintly impressed. :

Comparing casts with the associated V. obtusifrons, which is nearer than any
other now known, the present species differs in its greater obliquity, narrower
anterior end, much stronger umbonal sulcus, broader and better defined ligamental
area, and stronger as well as more coarsely crenulated hinge teeth.

*. Formation and locality.—Blue iimestone of the Trenton at Minneapolis, Minnesota.
Mus. Reg. No. 8335.

556 THE PALEONTOLOGY OF MINNESOTA.

[Vanuxemia umbonata.

VANUXEMIA UMBONATA, %. Sp.
PLATE XXXVIII, FIGS. 28—31.

Shell of medium size, tumid in the rostral and central parts, the hight about
one-seventh greater than the length; obliquely subovate, hinge line rather short, the
anterior extremity subangular and projecting a short distance beyond the beaks. .
Anterior margin gently convex, vertical, rounding neatly into the semicircular base;
posterior margin broadly convex, the junction with the hinge line obtusely angular.
Umbones evenly tumid, very prominent, the beaks curving forward*and down to the
hinge. Cardinal slope, concave; postero-cardinal portion of she!l compressed. Sur-°
face not well preserved in any of the specimens seen, apparently marked with rather
strong and somewhat irregular concentric lines of growth. Shell substance compara-
tively thin, so that the internal rostral and anterior thickening produces but a very
obscure sulcus on internal casts. Anterior muscular scar sharply defied, reniform,
of good size; posterior scar not observed; pallial line distinct in the anterior and
basal parts. Hinge plate rather strong, with a narrow ligamental area posterior to
the beaks; cardinal teeth long, nearly horizontal though distinctly curved, two in the
right valve; posterior lateral teeth four in the right valve, slender, oblique.

This species is doubtless closely allied to V. obtusifrons but may be distinguished
at once by its thinner shell, the greater projection of the anterior extremity of the
hinge, and the greater length and more nearly horizontal arrangement of the cardi-
nal teeth. Of the latter also there are only two instead of three, and they are not
crenulated as in the species. The posterior teeth again are more slender. V. hayniana
Safford, sp., is shorter and has a longer hinge line. One of the specimens is imper-
fect, so that it resembles Cyrtodonta cingulata, a rare species, occurring in the same
beds, and having similar surface markings. However, a comparison of external
characters alone reveals sufficient difference to render confusion between them highly
improbable, especially when the possibility of such an occurrence is borne in mind,
The hinge line of the Cyrtodonta, namely, is longer, the shell is more erect, the ante- -
rior end much longer, and the umbones, though more strongly convex, are on the
whole much less tumid. ;

Formation and locality.—Upper part of the mddle third of the Trenton shales, Minneapolis and St.
Paul, Minnesota. Also in the Black River horizon of the Trenton formation in Mercer county, Kentucky.

VANUXEMIA TERMINALIS Ulrich.
PLATE XXXVIII, FIGS. 33 and 34.
Cypricardites terminalis Uiricu, 1892. American Geologist, vol. x, p. 98.

Shell of medium size, moderately ventricose, extremely oblique, with the beaks
terminal, rather small, strongly incurved and projecting but little above the hinge

LAMELLIBRANCHIATA. Bay

Vanuxemia hayniana.]

line. Umbo full, and the whole surface neatly rounded. Outline obliquely acuminate-
ovoid with the anterior end narrowly rounded and projecting scarcely, if at all,
beyond the beaks, from which the margin slopes backward with a gentle curve into
the base; posterior end broad, uniformly rounded; cardinal margin straight, about
three-fifths as long as the diagonal length of the shell, rounding into the posterior
margin. Surface with faint wrinkles of growth and probably with finer concentric
lines. Shell substance thin. Hinge plate rather narrow, with two long posterior
and two or three short cardinal teeth in each valve. The latter are difficult to see
because of the closely incurved beaks. Anterior muscular impression, as seen in
casts of the interior, scarcely visible in a side view, being overhung by the side of
the Umbo. In an end view they appear like two narrow vertical lobes tapering
upward and placed just beneath the free portion of the beaks. Posterior scar very
faint, large, ovate, situated a short distance beneath the extremity of the hinge.
Pallial line distinct considering the thinness of the shell.

In the thin shell, its general form, and particularly in the character of the
anterior muscular impressions, V. terminalis reminds strongly of Ambonychia, It is
possible that this resemblance is merely coincidental, but I must say that I do not
believe it, even if I can not now present plausible arguments to show that it
expresses natural relationship. As a rule, it is not good policy to speculate in
paleontological questions, but in the present instance I may be pardoned when I
state my conviction that the Ambonychiide are an ofi-shoot from the same line of
development that produced Vanuxemia and the rest of the Cyrtodontide.

Seven of the species of Vanuxemia described in this report are found at Minne-
apolis in the same beds that have furnished V. terminalis. All of them occur as
casts of the interior, yet not one of the others is at all likely to be confounded with
the present species. The principal peculiarities of the latter are the terminal beaks,
almost hidden anterior muscle scars, the thin shell and the absence of the internal
ridge-like thickening which in nearly all species of the genus produces a more or less
well marked sulcus across the umbonal and anterior parts of casts.

Formation and locality.—Trenton limestone, Minneapolis and Cannon Falls, Minnesota. Also in
the ‘Lower Blue beds” of the Trenton near Beloit, Wisconsin.
Mus. Reg. Nos. 5100, 8320.

VANUXEMIA HAYNIANA Safford.
PLATE XXXVIII, FIG. 32. ALSO FIG. 36-VI, P. 479.
Cyrtodonta hayniana SAFFORD, 1869. Geol. Tenn., pl. F., fig. 1.
Cypricardites haynianus ULRicn, 1892. Nineteenth Ann. Rep: Geol. and Nat. Hist. Sur. Minn., p. 240.

Cypricardites triangularis SARDESON, 1892. Bull. Minn. Acad. Nat. Sci., vol. iii, p. 338.

Shell of medium size, moderately convex, oblique, broadly subovate or obscurely
quadrate, narrowing anteriorly, the hight and length respectively as nine is to ten;

558 THE PALEONTOLOGY OF MINNESOTA.

[Vanuxemia hayniana.

hinge line nearly straight, rather long, terminating subangularly behind; posterior
margin broadly rounded, slightly oblique, generally forming, with the basal margin
a semicircle drawn to a diameter but little shorter than the length of the shell, and
equalling the greatest hight; anterior end projecting very little beyond the beaks,
nicely rounded from the end of the hinge, sloping backward in the lower half and
passing very gradually into the basal line. Beaks only moderately prominent,
strongly incurved, approximate; umbones full, uniformly convex to the beginning
of the faintly concave dorsal and posterior slopes. Surface marked with more or
less obscure and unequal concentric lines, some of them often, especially near the
margin of old shells, being of a strongly lamellose character.

Hinge of moderate strength, the plate varying between 2 and 3 mm. in width at
the middle in adult specimens; about half of the width taken up by a long and very
finely lined ligamental area. Posterior lateral teeth constantly three in each valve,
nearly straight, ranging at an angle of about 40° with the hinge line. Cardinal teeth
varying in number and size. Asa rule they are at least 10° more oblique than the
posterior ones and normally of nearly equal size, finely toothed or striated and three
in each valve. The variations are evidently due to irregularity of development,
Rarely there are two large ones with a small one on each side; more commonly one.
two, or even all three will be divided, so that the total number may reach six.
Anterior muscular scar sharply defined, semicircular; posterior scar ovate, as usual
very faintly impressed; pallial line quite distinct, except in the posterior part.
Umbonal cavity small, compressed; anterior internal thickening of the valves gen-
erally rather sharply defined on the inner side.

Casts of the interior, the only condition in which the species has been found in
Minnesota, have small compressed pointed and scarcely incurved beaks, projecting
slightly beyond the hinge line and situated farther behind the anterior extremity of
the shell than is the case on the exterior. The ridge immediately behind the
anterior flattening or sulcus is well marked, as is also the pallial line and the ante-
rior muscular scar. Indeed the natural casts correspond exactly with artificial ones
prepared from typical Tennessee and Kentucky specimens of the species.

This is a widely distributed and well marked form, about which a number of
closely related species or varieties are grouped. One of these, V. subrotunda, occurs
in Minnesota, but in lower beds than the typical form. It is distinguished by its
more circular outline. Another, V. abrupta, from the Galena of Fillmore county, is
more easily separated by its more nearly terminal beaks, very obtuse anterior side,
thinner shell, and in wanting the ridge which marks the casts of V. hayniana. A
third form is found in the upper Trenton of Kentucky. Being a smaller shell I
called it nana (Cypricardites nanus Ulrich, 1892. Nineteenth Ann, Rep. Geol. and Nat,

a4

LAMELLIBRANCHIATA. 559

Vanuxemia subrotunda.] c

Hist. Sur. Minn., p. 239.) On comparison it proved to have a thinner shell, to be more
erect and more rounded in outline, also more ventricose and with a stronger umbonal
ridge, while there are only two cardinal teeth instead of three or more. A fourth
form I propose soon to describe, in one of the periodicals, under the name of
V. gibbosa. -It is from the lower Trenton of central Kentucky, and differs from
the present species in being more gibbous, in having larger umbones, almost
terminal beaks:and more obtuse anterior side. A fifth is associated with the
preceding in Kentucky, and also occurs in Tennessee. It is a very thick shell and
attains to larger size than V. hayniana, from which it differs further in its form
which is higher and straighter and more obtuse in front. But the principal differ-
ence lies in the ligamental area which is at least twice as high as in adult examples
of Safford’s species. The area is shown in four specimens and in all of them its hight
is 4 mm. or more at the middle and in one it is quite 5mm. For this form | propose
the name Vanuxemia cardinata. Finally a sixth form of this type is known to me
from about twenty very perfect specimens that I owe to the liberality of Prof. J. M.
Safford. He collected them at “Haynies,” the locality in Smith county, Tennessee
from which he obtained also the types of his “Cyrtodonta hayniana.” Yor the present
I shall arrange these specimens as a small variety of V. gibbosa, since they agree
much better with that species than with true V. hayniana. :

Formation and locality.—The types of this species are from the Trenton limestone (middle Nashville
beds of Safford) in Smith county, Tennessee. In Kentucky the species occupies two narrow horizons
separated by more than 100 feet of strata. The first is at the base of the Trenton limestone in Mercer
county at a point about three miles south of High Bridge, where the decomposed limestone has left
numerous silicified shells and cystidrans. The second horizon, which is near the top of the Trenton,
is exposed at several points along the Cincinnati Southern railroad between Burgin and Danville. In
Minnesota the species seems to be restricted to the Galena shales, in which it occurs as casts of the
interior at several localities in Goodhue county and at St. Paul. Good specimens are rare.

VANUXEMIA SUBROTUNDA ey Sp.
PLATE XXXVIILI, FIGS. 36—38.

This species differ from V. hayniana Safford sp., to which it is doubtless very
closely allied, in its more uniformly rounded outline, broader anterior end and
shorter hinge line, and in having the beaks smaller and situated farther behind the
anterior extremity. The convexity of the valves also is less, and the shell is thin-
ner, particularly in the umbonal and anterior parts where the internal thickening
is so little that no perceptible sulcus nor ridge is left in casts of the interior. For
the same reason the beaks on casts must be more rounded and larger, so that how-
ever much the exterior of the two shells may resemble each other, casts of the
interior would be distinguished very readily. V. nana Ulrich, from the upper Trenton
in Kentucky, is asmaller shell; with more ventricose valves, better defined umbonal

560 THE PALEONTOLOGY OF MINNESOTA.

«

[Vanuxemia abrupta.

ridge, and longer hinge line. Of associated species, Crytodonta glabella Ulrich, has a
similar outline, but there is no relationship between them since that species is as
true a Crytodonta as this is a Vanuxemia.

Formation and Locality.—In the upper part of the middle third of the Trenton shales, Goodhue
county and Chatfield, Minnesota.

VANUXEMIA ABRUPTA 2. Sp.

PLATE XXXVIII, FIG. 39—44.

» Shell a little beneath the medium size for the genus averaging 20 mm. high and
24 mm. long; rounded or subquadrate in outline, with subterminal beaks, tumid in the
umbonal region and in front of the center, the anterior end very obtuse, the surface
in the upper part rounding abruptly inward to the edges of the valves so that in a
side view of casts of the interior the sharply defined anterior muscular scar is quite
hidden beneath the filling of the umbones. Hinge line straight, long, terminating
more or less abruptly posteriorly; posterior margin broadly rounded, occasionally
nearly erect, usually a little oblique; anterior side truncated above, rounding below;
base rounded. Casts have full and rounded and well incurved beaks, and the con-
vexity of the surface continues without a sign of the sulcus and ridge exhibited by
the casts of so many species of this genus. As near as can be determined from the
impré&sions, the hinge plate was narrow and bore two, in one case apparently three
slender posterior lateral teeth and two cardinal teeth in each valve. Pallial line and
posterior muscular impression very obscure. Surface almost smooth, the best
specimens only showing remains of fine concentric lines.

This well marked species is believed to be related to V. nana and V. hayniana,
but the subterminal beaks and obtuse anterior end will distinguish it at once. From
V. terminalis of the lower Trenton, which certainly is also very much like it and
perhaps a more natural ally, it is separated by the more erect form.

Formation and locality.—Middle Galena, Fillmore and Goodhue counties, Minnesota.

Vanuxemia niota Whitfield (?Hall).
PLATE XXXVIII, FIG. 35.

?Cypricardites niota HALL, 1861, Rep. Supt. Geol. Sur., Wis., p. 20; also 1862, Geol. Rep., Wis., vol. i,
p. 38, Fig. 8, p. 438.
Cypricardites niota WHITFIELD, 1882, Geol. Rep., Wis., vol. iv, p. 208.

Iam very much inclined to doubt that this species, a specimen of which was
submitted to Prof. Whitfield, is the same as the one described by Prof. Hall. If it is,
then the original description is anything but accurate.*

* Hall’s original description of Crypricardites niota reads as follows: “Shell broadly subovate, broadest at the posterior
end; umbones very gobbous, beaks incurved, little elevated, situated about one-fourth of the length of the shell from
the anterior end. Oardinal line straight or little curved; anterior, posterior and basal margins rounded. Anterior muscular ~
impression situated near the cardinal line, well defined; posterior imprint obscure. Surface of the shell marked by con-
centric lines of growth. This species differs from O. rotundata in being more oblique, in the straighter cardinal line, and less
ventricose form. It is intermediate between that species and C. ventrecosa, from which it difiers in less obliquity and the
greater length from beak to base.” ‘Length, one inch and a quarter; hight, one inch.”

LAMELLIBRANCHIATA. 561

Vanuxemia wortheni.]

As it reads I should say that he refers to a species of Cyrtodonta like C. glabella or
C. persimilis and not to a Vanuxemia which the shell here under consideration
undoubtedly is. The latter differs in at least two important respects from the
characters brought out in Hall’s description, and either one would in my opinion, be
sufficient to defeat specific identity. Thus, he ‘says the beaks are “situated about
one-fourth the length of the shell from the anterior end,” whereas in Whitfield’s
niota they are much nearer the anterior extremity; then he gives the impression
that the anterior, posterior and basal margins are almost uniformly rounded, while
in the present species, the outline is always more or less quadrangular. Under the
circumstances I might have been justified in proposing a new name, but as the
questions involved would still be open (a study of the original of Hall’s description
alone can answer them), it seemed best to refer to the species provisionally as

above.

Vanuxemia niota Whitfield (?Hall) sp., is closely related to V. hayniana Safford
sp. and V. gibbosa Ulrich. From the first it is distinguished by its greater convexity
and length, more anterior and larger beaks, and almost rectangular instead of
rounded anterior side. The cast figured on plate xxxvim preserves the impressions
of the hinge teeth. The cardinal teeth were rather small, oblique, and numbered
four in each valve. The posterior teeth were slender, nearly horizontal, and three
in number. In V. gibbosa the anterior margin forms a wider angle with the hinge
line, the shell was a little thicker, the hinge stronger, and the cardinal teeth larger,
not exceeding three in number and less oblique. In artificial casts of that species
the anterior muscular scar proved to be comparatively larger, and to project farther
anterior to the filling of the beaks, which again are of larger size than in niota. JV.
wortheni of the Galena belongs to the same group of species but is a much larger
and rounder shell, and in casts has more compressed and less incurved beaks.

Formation and locality.—Top of the ‘‘ Lower Blue Beds,” and base of the ‘‘ Upper Buff Beds” of the
Trenton formation at Beloit and Mineral Point, Wisconsin, and Rockton, Illinois.

Mus. Reg. No. 8321, 8325.
VANUXEMIA WORTHENI Ulrich.
PLATE XXXIX, FIGS. 6 and 7.

Cypricardites, sp., undet., Meek and WorrueEn, 1868. Ill. Geol. Sur., vol. iii, p. 311.

Cypricardites wortheni ULRicH, 1888. Amer. Geol., vol. 1, p, 189.

Shell large, moderately ventricose, suberect, subcircular, the length a little
greater than the hight, the beaks nearly terminal, the dorsal margin almost straight,
rather long and with the extremities rounding abruptly, the anterior one scarcely

projecting beyond the point of the beaks; the rest of the outline rounded with the
—36

562 THE PALEONTOLOGY OF MINNESOTA.

(Vanuxemia decipiens.

postero-basal part a little more curved than elsewhere. Surface rather uniformly
convex in the central and umbonal regions, with the point of greatest convexity a
trifle in front of the middle and unusually low.

Casts of the interior show that the shell was thickened internally on the anterior
part, that the posterior side of the thickening was margined by a slightly oblique
narrow groove or sulcus which left a blunt though well marked ridge on the cast
extending down from a little behind the beaks to below the middle of its sides.
Beaks very prominent in the casts, greatly compressed, but little incurved, hollow
upon the inner side, an unusually large space left between them, showing that the
hinge plate was much thickened in this part. The exact width of the hinge plate is
unknown, but it must have been considerable and probably greater than the average,
especially at the ends where it was bent down to make room for the large teeth.
Of the cardinal teeth there were three in the right valve and the same number or
only two in the left. They were of large size and rather strongly curved and oblique.
The posterior teeth were strong, scarcely curved and oblique, but their number is
unknown. Anterior muscular impression of medium size, rounded, sharply defined,
but not very deep, excavated out of the anterior end of the hinge plate, the pair
forming (in an anterior view of the cast) a narrow lobe partly between, but mostly
in front of the filling of the beaks. Pallial line sharply defined in the anterior half,
obscure behind. Posterior muscular impression very faint, large, situated immedi-
ately beneath the lateral teeth. A large cast has a hight of over 50 mm.

This shell is the largest known to belong to the genus. It belongs to the group
of species of which V. hayniana Safford may be regarded as typical, but differs from
them all in having the point of greatest convexity situated at the center instead of
above the center. It is scarcely necessary to compare the species in detail with the
numerous forms to which it is more or less nearly related, since ordinary specimens
are distinguished at once by their unusual size.

Formation and locality.—Middle or upper part of the Galena, Mount Carroll, Illinois.

VANUXEMIA DECIPIENS, 2. Sp.

PLATE XXXIX, FIGS. 1-5.

Shell rather small, strongly convex, obliquely ovate, highest posteriorly, the
length of a large specimen 23 mm., its hight 18 mm. Hinge line straight, two-
thirds as long as the shell, terminating subangularly behind, rounded in front;
posterior margin slightly oblique, strongly rounded and somewhat prominent in the
lower half; basal line moderately convex, ascending from the posterior third or
fourth; anterior end narrowly rounded, very short, the greater part of it occupied

LAMELLIBRANCHIATA. 563

Matheria ]

by the muscular scar. Beaks of moderate size and fullness, incurved, the anterior
half slightly flattened in the casts. This flattening, which is produced by the usual
internal thickening of the anterior part of the shell, extends obliquely backward
and downward from the beaks toward the middle of the ventral edge. Anterior
muscular scar somewhat uniform, not as sharply defined below as is usual for the
genus, very distinct, however, and partly overlapped above by the fillimg of the
beaks. Pallial line sharp in the anterior two-fifths, obscure behind. Posterior
muscular impression too light to be determined with certainty. Hinge plate nar-
row, with two slender horizontal posterior lateral teeth in the left valve and three
in the right. Cardinal teeth unknown.

This species is associated with several of Cyrtodonta that, under ordinary condi-
tions, are not easily distinguished. The feature to be chiefly relied upon in separating
them (i. ¢., the character of the anterior muscular scar) is usually obscured by crys-
tallized remnants of the shell. When these are removed and a clean cast of the inteior
has been produced the difficulties will have been overcome, since the l’anuxemia may
then be distinguished at once from the Cyrtodonta by the much greater distinctness
and character of the anterior muscular sca: ‘Comp. figs. 3 and 42 on plate xxx1x.)

Formation and locality.—Trenton limestone, Minneapolis, Minnesota.
Mus. Reg. No. 5100; 626,

Genus MATHERIA, Billings.

Matheria, BrttrNes, 1858. Can. Nat. and Geol., vol. iii, p. +40.

Shell equivalve, very inequilateral, oblong quadrate or suboval; beaks small
anterior. Surface marked with concentric growth lines only. Hinge of moderate,
strength or rather weak, with external linear ligamental area posterior to the beaks,
two small, divaricating cardinal teeth beneath the beak of the left valve and only
one in the right; no lateral teeth. Adductor impressions two; the anterior one
smaller and better defined than the posterior. Pallial line simple, obscurely defined.

Type: Matheria tenera Billings.

Only four or five species known to me have the characters of this genus. They
are all small shells and with one exception belong to the Trenton. J. fenera is from
that horizon in Canada, one or two undescribed species occur in Kentucky, and J,
rugosa in Minnesota, while the Modiolopsis recta Hall, which is a true Matheria,
belongs to the Niagara of Wisconsin and Illinois.

Marueria ruGosa Ulrich.
PLATE XXXVI, FIGS. 29 and 30.
Matheria rugosa Utricu, 1892. Nineteenth Ann. Rep. Geol. and Nat. Hist. Sur., p. 241.
Shell large for the genus, trapezoidal, widest posteriorly, with the beaks nearly
terminal, small, incurved, projecting slightly above the hinge; a strongly convex

564 THE PALEONTOLOGY OF MINNESOTA. [ Whitella.

umbonal ridge. Anterior end descending abruptly from the beaks, below rounding
sharply into the nearly straight ventral border; posterior margin produced and
strongly rounded in the lower half, obliquely subtruncate above, forming an obtuse
angle at the junction with the hinge line; the latter very gently arched. Surface
marked with strong concentric wrinkles and finer lines of growth. Shell substance
of moderate thickness.

Hinge plate strong, flat, slightly arcuate, the upper half of the width posterior
to the beaks, finely striated lengthwise. Cardinal teeth small, situated just beneath
the beaks, directed toward the postero-basal margin, with one in the right valve and
on each side of it a deep socket for the reception of the two teeth of the left valve.
Anterior muscular scar rather distinct, subcircular, situated immediately beneath
the teeth.

Several additional specimens of this well marked species were collected during
the summer of 1892, among them an entire left valve showing the hinge. This has
two cardinal teeth and no posterior laterals, so that there can be no longer any
question as to the generic position of the shell. Only two other species belonging
to this genus are known to have been described. These are M. tenera Billings and
_ M. recta (Modiolopsis recta Hall), from both of which M. rugosa differs in the much
greater hight of the posterior end. The shape of the shell reminds one greatly of
Ischyrodonta and certain species of Cyrtodonta, but in the former the cardinal teeth
are much stronger and the ligament internal instead of external. The hinge of
Cyrtodonta, with its posterior lateral teeth and curved, more numerous, and longer
cardinal teeth, is quite different, but when the interior is hidden the collector may
experience some trouble in distinguishing the species from the associated Cyrtodonta
afinis. Still, there is one difference that will serve his purpose very well, namely,
the anterior end of the latter is rounded and somewhat produced beyond the beaks,
whereas it descends abruptly from the beaks in the Matheria.

Formation and locality.—Upper part of the middle third of the Trenton shales, about six miles south
of Cannon Falls, Minnesota.

Genus WHITELLA, Ulrich.

Whitella, ULRICH, 1890, Amer Geol., vol. vi, p. 176.

Shell thin, obliquely quadrangular or suboval, equivalve, inequilateral, more or
less ventricose. Umbones very prominent, the beaks strongly incurved; umbonal
ridge prominent, subangular or sharply rounded. Cardinal margin straight or
slightly convex, the edges inflected to form a sharply defined escutcheon extending
beyond the beaks sometimes quite to the anterior extremity of the shell; area finely
striated longitudinally. Hinge line straight, from one-half to two-thirds the length

LAMELLIBRANCHIATA. 565
Whitella obliquata.]

of the shell, with two to five rather obilque folds or teeth in front of the beaks.

Posterior portion of hinge apparently edentulous. Ligament probably beth external v a rm phe m
pend eoetta Diiee Jateee Only aiOie wae BOsherior taare OF the-hinge line, where it-was
supported-by an internal ridge in each valve. Two simple adductor impressions, the

posterior one very faint; pallial line simple, marginal; interior of shell lined with a

nacrous film. Surface of shell with fine concentric lines, and sometimes with stronger
concentric undulations.

Type: W. obliquata Ulrich.

No more easily recognized genus of Lamellibrancliiata than this is known from
the Lower Silurian rocks, and of those restricted to that system, none is more
important in the way of species and distribution. Twelve species, nine of them
Trenton, the rest from the Hudson River group, are described and figured in this
work. ‘Two others were described by me in 1890, from the Cincinnati group of Ohio
as W. umbonata and W. subovata, while another pair, hindi and plebeia, from the
Hudson River rocks of Anticosta, were doubtfully referred by Billings to his genus
Cyrtodonta. With the latter species Billings describes two others as Cyrtodonta ?
sigmoidea and C. acutumbona (1866, Catal. Sil. Foss. Anticosti, pp. 15 and 49), which
may turn out to belong to Whitellu. The Cypricardites carinata Meek, from Cincin-
nati, Ohio, also belongs here, while a very large species from the upper beds of the
same formation remains to be described. Species of this genus have been referred to
Dolabra McCoy, Cypricardites Conrad, and Cyrtodonta Billings. McCoy describes his
genus as containing inequivalve shells in which the hinge is edentulous. Cypricardites
and Cyrtodonta both have well developed posterior lateral teeth and quite different
cardinal teeth. In the latter also the shell is thicker and the ligamental area never
so well developed, nor is the umbonal ridge ever so prominent as is commonly the

case in Whitella.

WHITELLA oBLIQuATA Ulrich.
PLATE XL, FIGS. 31 and 32.

Whitella obliquata Uric, 1890. Amer. Geol., vol. vi, p. 177.

Shell large, oblique, subrhomboidal in outline, produced in the postero-basal
region, ventricose, with point of greatest convexity above the middle; beaks rather
small, prominent, slightly incurved, situated nearly one-third of the length of the
hinge line from its anterior extremity; umbonal ridge well marked, the cardinal
slope concave. Anterior end small, narrowly rounded above, merging gradually into
the evenly and only moderately convex ventral margin. Posterior end sharply
curved and produced below, gently convex and sloping forward in the upper half to
meet the slightly convex, cardinal margin. Escutcheon well marked, wide, shallowest

566 THE PALEONTOLOGY OF MINNESOTA.

[Whitella quadrangularis.

in front of the beaks. Anterior muscular scar elongate. Hinge thin, simple posterior
to the beaks, in front of them, with one long and slender horizontal tooth and
several slightly oblique short teeth above it. The dimensions of a cast of the inte- .
rior, of the average size, are as follows: greatest length, 50 mm.; greatest hight, 38
mm.,; greatest convexity, 24mm. A large specimen is59 mm, long and 42 mm. high.

In W. sterlingensis M. and W. sp., the umbonal ridge is much stronger, the cardinal
area much wider, the anterior end short, the posterior margin different, especially
below where it is narrower, and the length from the beak to the postero-basal
extremity comparatively greater. W. quadrangularis Whitfield, sp., is a more convex
shell, not so oblique, and has a wider cardinal area, and larger beaks. For compari-
son with Trenton species see their descriptions.

Formation and locality.—Hudson River group, near Spring Valley, Minnesota. In Ohio and Indiana
the species is not uncommon in the upper beds of the Cincinnati group.

WHITELLA QuADRANGULARIS Whitfield.
PLATE XL, FIGS. 28—30.
Cypricardites quadrangularis WHITFIELD, 1878. Jour. Cin. Soc. Nat. Hist., vol. i, p. 138.

Shell of medium size, gibbous, rather erect and nearly rounded or quadrangular
in outline, with very large incurved, though widely separated, subcentral beaks, over-
hanging the proportionally short but unusually wide ligamental areas. Length and
hight subequal, the latter probably a little the greater; thickness more than two-
thirds of the hight. Umbonal region very prominent, rounded anterior to the
obtusely angular and rather inconspicuous umbonal ridge; behind the ridge the
surface is a little concave and slopes abruptly toward the magin; anterior slope
similarly abrupt and concave. Anterior end sharply rounded and most prominent
at the extremity of the hinge; ventral and posterior margins sometimes forming a
regular semicircle, but usually a slight prominence is perceptible in the postero-
basal regions, causing a straightening of the posterior margin. Surface marked
with somewhat irregular concentric lines and wrinkles of growth.

In casts of the interior the anterior muscular scar i; uncommonly well defined
for the genus, and immediately above them, a pair of depressions forming the ante-
rior end of the cardinal area, is also an unusual feature. Furthermore, a slight
vertical furrow on the umbones reminds of Cyrtodonta. Yet, despite these peculiar-
ities, am convinced that the species belongs to Whitella rather than to Cyrtodonta.
This view is strengthened by the facts that the shell was very thin and covered on
the inner side by a delicate pearly nacre, parts of which are preserved on the cast
represented by figure 29. Such a film has been observed on casts of other species of
Whitella, but has never been noticed on similarly preserved species of Cyrtodonta.

LAMELLIBRANCHIATA. 567

Whitella sterlingensis.]

In drawing up the above description I have made use of the original type of the
species which was borrowed from the museum of the Cincinnati Society of Natural
History. This specimen is a mold of the exterior and has been compressed in such
a manner that the outline is now unnaturally quadrangular, the umbonal ridge too
prominent and the beaks too narrow. I have compared it very carefully with the
northwestern specimens, which are casts of the interior, and while I admit freely the
the possibility of error, my conclusion for the present is that they are specifically
identical.

Compared with other species of Whitella it will be found that the shell is more
erect and shorter, and the cardinal area wider than in any other known. An asso-
ciated form, Cyrtodonta grandis, var luculenta Sardeson, has much smaller beaks, while
they are also nearly in contact, the ligamental area being very much narrower.

Formation and locality—Upper beds of the Cincinnati group at Clarksville, Waynesville and other
localities in Ohio. The northwestern specimens were obtained from an equivalent horizon at Savannah,
Illinois, and Spring Valley, Minnesota.

WHITELLA STERLINGENSIS Meek and Worthen.
PLATE XLI, FIGS. 27 and 28.

_Dolabra sterlingensis MEEK and WortTuHEN, 1866. Proc. Acad. Nat. Sci. Philad., p. 260; also 1868,
Geol. Sur. Ill., vol. iii, p. 339.

Not Cypricardites sterlingensis ? MEEK, 1873. Pal. Ohio, vol. i, p. 133.

Original description: “Shell rhombic-cordate, being cordate in outline, as seen in
an anterior and posterior view, and obliquely rhomboidal, as seen from either side.
Posterior margin obliquely truncated, with a long slope, which is slightly convex
above and faintly sinuous near the middle; posterior basal extremity produced
obliquely backwards and downwards, with a more narrowly rounded or subangular
outline; basal margin ascending forward, with a moderately convex curve, and
rounding up more or less gradually into the very short or almost obsolete anterior
side; hinge line short; cardinal area moderately developed. Beaks prominent,
placed nearly over the anterior margin, strongly incurved and compressed antero-
posteriorly. Umbonal ridges very prominent, subangular, and extending from the
beaks obliquely to the posterior basal extremity at an angle of about 45° below the
horizon of the hinge, thus dividing each valve into two subequal areas, of which the
one behind is flattened or slightly concave between the ridge and the moderately
prominent postero-dorsal edge, and that in front and below it convex. (Hinge and
interior unknown.)

“Greatest length, measuring obliquely from the beaks to the posterior basal
extremity, 2.20 inches; diameter, at right angles to the same, 1.50 inches; convexity
of the two valves when closed, 1.50 inches,”

56S THE PALEONTOLOGY OF MINNESOTA.

[Whitella compressa,

The great prominence and sharpness of the umbonal ridge, the decided flattening
of the postero-dorsal region and the narrowness of the posterior extremity are the
features that distinguish the species from all the others referred to the genus, except
W. hindi Billings sp., W. carinata Meek sp., and W. truncata Ulrich. The first of these
exceptions is not so high, less gibbous, less oblique, has a more prominent and less
broadly rounded anterior side, straighter posterior margin, narrower beaks and a
cardinal area or escutcheon that is a little longer but not nearly so wide. The other
two are sufficiently distinguished by their much smaller size.

The specimen described by Meek in the Ohio Paleontology (loc. cit.) and doubt-
fully referred to this species is certainly distinct. It my belong to W. hindi Billings,
or to W.wmbonata Ulrich, both of which it resembles more closely than W. sterlingensis,
especially in the prominence of the anterior end, which of itself precludes all possi-
bility of its identity with the present species. That it really belongs to one or the
other of the two species mentioned it would not now be safe to say, since I have no
means of learning to what extent the specimen may have suffered from compression.

Formation and locality.—The type specimen was found in the upper beds of the Cincinnati group
at Sterling, Illinois. A small distorted shell from the Hudson River group near Spring Valley, Min-
nesota, may belong here, but I cannot say as much for any specimen seen from the equivalent strata
of Ohio and Indiana, despite the fact that the species is commonly believed to occur there.

WHITELLA compressa Ulrich.
PLATE XLI, FIGS. 6—9.

Whitella compressa ULRICH, 1890. Amer. Geol., vol. vi, p. 180.

This shell has an outline very similar to that of W. obliquata, yet differs con-
spicuously from that species in having much less gibbous valves, the thickness in
that species equalling about one-half of its greatest length, while in W. compressa
the length is more than two and one-half times the convexity. And yet the length
of the latter is comparatively a little less than in the Hudson River group species.
Comparing the two species critically we find further that in W. compressa the umbonal
ridge is much less developed and the outline at the extremities of the hinge some-
what different, the posterior part being a little more sharply rounded, while anteri-
orly the hinge projects farther beyond the beaks and in a straighter line, so as to
form an angular junction with the anterior margin. An undescribed form found
associated with W. obliquata in Ohio, and which I shall call W. ohioensis, attains a
greater size, but agrees in all its specific characters much more closely with the
present species. Indeed the agreement is so close that we may be justified in
regarding it as a reapparition of W. compressa, the only difference so far detected
with certainty being a slight one in the outline. The Ohio form, namely, is a little
narrower across the posterior half of the shell, I expect, however, that when more

LAMELLIBRANCHIATA. 5

Whitella concentrica.]

perfect material can be compared other differences will become apparent, especially
in their hinges and muscular impressions, these parts appearing to be somewhat
stronger in the Trenton shales species.

Formation and locality.—Middle third of the Trenton shales, Minneapolis and St. Paul, Minnesota.

WHITELLA conceNTRICA Ulrich.
PLATE XLI, FIGS. 2 and 3.

Whitella concentrica ULRICH, 1892. Nineteenth Ann. Rep. Geol. and Nat. Hist. Sur. Minn., p. 247.

Shell rather beneath the medium size, oblique, ventricose, widest posteriorly,
trapezoidal; beaks large, prominent, incurved; umbones full, with a sharply rounded
ridge or line of gibbosity extending backward from the beaks to the posterior
extremity of the shell. Cardinal and posterior slopes shghtly concave. Anterior
end short, narrowly rounded; ventral edge very gently convex; posterior end pro-
duced and sharply rounded in the lower half, more gently convex and sloping rapidly
forward above, merging gradually into the curve of the dorsal side. Hinge line about
half as long as the shell, with the edge inflected so as to form a narrow escutcheon,
extending but little, if at all, in front of the beaks. Internal ligamental supports
leave a distinct impression on each side of the postero-cardinal margin in casts of
the interior. Anterior muscular scars distinct though faintly impressed, situated in
the antero-dorsal angle. Surface of casts, especially in the lower and posterior parts,
marked with fairly distinct, rounded, concentric folds.

The concentric undulations are stronger in this species than in any other known
tome. It is shorter than W. pracipta, more ventricose than W. compressa, and has
much fuller umbones than W. obliquata. In W. scofieldi the surface is not undulated,
the anterior end is subangular above, and the umbonal ridge sharper.

Formation and locality.—Middle third of the Trenton shales at Minneopolis, Minnesota.

WHITELLA RUGATINA, 7. SD.

PLATE XLI, FIG. 1.

Shell subovate or obscurely trapezoidal, moderately gibbous, with well shaped
and prominent umbones and strongly incurved beaks situated one-fourth of the
length of the shell behind the anterior extremity. Umbonal ridge moderate, rounded
except immediately behind the beaks. Escutcheon narrow, not extending in front
of the beaks. Surface of casts marked with numerous, rather small, concentric
furrows, which in parts may be quite regular, but in others are thrown into bundles
so as to produce? obscure] undulations. Hinge unknown, muscular and_ pallial
impressions very faint.

570 THE PALEONTOLOGY OF MINNESOTA.

[Whitella megambona.

The specimen figured has the following dimensions: From the postero-basal
margin to the antero-cardinal angle, 33 mm.; from the same point to the umbones,
31 mm.; from the postero-cardinal margin to the antero-basal margin, 26.5 mm.;
greatest or posterior hight, 24.7 mm.; greatest convexity, 16.5 or 17 mm.

Though comparable in a general way with a number of species referred to the
genus, the relations are not very close in any case. In the matter of outline it agrees
best with W. compressa and W. ohioensis, but the umbones are larger, the valves more
convex, and the surface markings much better defined, especially on casts of the
interior. The umbonal ridge is not strong enough for W. scofieldi, and the umbones
too small for W. concentrica, while in the outline it differs iu a similar manner from
both of those species. Finally, in W. subcarinata and W. ventricosa Hall, sp., the
anterior end is shorter.

Formation and locality.—Middle third of the Trenton shales, Minneapolis, Minnesota.

WuitELLA mMEGAMBONA Whitfield.
PLATE XLI, FIGS. 4 and 5.

Cypricardites megambonus WHITFIELD, 1877. Ann. Rep. Geol. Sur. Wis., p. 73. Also 1882, Geol., Wis.,
Whitella megambona ULRICH, a0 ees vol. vi. p. 384.

Shell of medium size or less, oblique, subelliptical in outline, very gibbous, the con-
vexity of the closed valves equalling very nearly the shorter of the oblique diameters,
and about two-thirds of the distance from the beaks to the postero-basal extremity.
Umbones very large, tumid, with the beaks strongly and obliquely incurved, their
points being brought into close proximity; umbonal ridge prominent, subangular
near the beaks but becoming obtuse in receding from them; point of greatest con-
vexity somewhat behind the middle of the shell. Hinge line very short, posteriorly
passing rather gradually into the posterior margin; the latter is somewhat oblique
and broadly rounded to the base where the outline turns rather sharply forward into
the basal line, which continues with a uniform curve to the ‘narrowly rounded—
almost angular—anterior extremity; the latter projects about one-ninth of the longer
diameter of the shell beyond the anterior side of the umbones. Surface marked by
irregular concentric lines of growth, and distant obscure undulations. Anterior to
the umbonal ridge the surface is rather strongly convex, while the posterior and
cardinal slopes are flattened and exhibit along the center a more or less distinct
sulcus. Escutcheon very short and narrow. Internal ligament supports, unusu-
ally long, in casts leaving a well defined furrow on each side of the hinge line,
extending from the upper part of the posterior margin almost to the beaks. Car-
dinal teeth apparently as in W.scofieldi. Anterior muscular scar shallow, rather,

~l
—

SE A aa ee LAMELLIBRANCHIATA. 5
small, rounded, situated in the antero-dorsal angle. Posterior scar and pallial line
undetermined.

In most specimens there are two or three, thin, parallel and oblique ridges on
each side at the extremity of the hinge. These opposed sets of ridges are separated
by an interval in adult examples, but it is scarcely to be questioned that in an earlier
stage in the development of the shell they represented posterior lateral teeth similar
to those of Cyrtodonta. This fact must have an important bearing upon the question
of genealogy, but, in the absence of any knowledge of similar types in earlier strata,
it is not now possible to discuss it with anything like certainty of arriving at a true
solution of the question.

This is a well marked species and one that is not likely to be confounded with
any, of the associated shells. Its nearest congeners seem to be |W. scofieldi and W.
sterlingensis M. and W., sp., the latter particularly, but in both of these species the
umbonal ridge is more conspicuous and the outline different. The former again has
a longer escutcheon and hinge, much larger anterior end and more prominent
postero-cardinal angle, while in the latter the shell is more oblique, the posterior
angle narrower, the cardinal area much wider and the beaks farther apart.

Formation and locality.—Lower Trenton limestone, near Beloit, Wisconsin and Minneapolis, Minn.

Wuitetta scorretpr Ulrich.
PLATE XLI, FIGS. 17—21.

Whitella scofieldi ULRicuH, 1890. Amer. Geol., vol. vi, pp. 181 and 382.

Shell of medium size, strongly convex, moderately oblique, subtrapezoidal in
outline, with the hinge line longer, straighter and better defined than usual. Ante-
rior end unusually long and wide, the outline gently rounded from the subangular
junction with the hinge line; basal margin slightly convex, oblique, descending to the
strongly rounded postero-basal angle; posterior margin subtruncate, slightly oblique
and but little convex in the upper half. Umbones prominent, subcarinate behind, with
the beaks approximate, obliquely enrolled and situated a little more than one-third of
the length of the hinge line behind its anterior extremity. The umbonal ridge is a
conspicious feature, although becoming obsolete before reaching the postero-basal
margin, Posterior to the ridge the surface is distinctly concave; in front and
beneath it convex. Surface marked by rather distinct concentric lines of growth,
of which the marginal ones may, in old examples, assume a sublamellose character.
Escutcheon high but narrow in a dorsal view, finely striated longitudinally and not
extending anterior to the beaks. Internal ligamental supports appearing as a double
ridge in each valve beneath the posterior half of the escutcheon. Anterior hinge

572 THE PALEONTOLOGY OF MINNESOTA.
[Whitella truncata.

teeth two in each valve, elongate, slightly curved, nearly horizontal. Muscular scars
and pallial line faint, not well determined.

This species is more convex and has a more distinct umbonal ridge than W.
compressa, and a longer hinge line and larger anterior end than W. megambona, while
the basal margin is more oblique and the anterior end much larger than in W, sub-

carinata.

Formation and locality—Upper part of middle third of the Trenton shales, St Paul, and near
Cannon Falls, Minnesota, Also in the Trenton limestones (‘‘ Upper Buff beds”) near Beloit, Wisconsin.

WHitELia TRUNOATA Ulrich.
PLATE XLI, FIGS. 10—14.

Whitella truncata Utricn, 1890. Amer. Geol., vol. vi, p. 385.

Shell small, very oblique, ventricose, subrhomboidal in a side view. Beaks
nearly terminal, prominent, of moderate size, obliquely enrolled; umbones and
umbonal ridge full, the latter angular and traceable to the postero-basal angle.
Cardinal slope sharply defined and distinctly concave; anterior and basal slopes
slightly convex and very rapid. Anterior end very short, scarcely projecting beyond
the beaks, narrowly rounded, then sloping rapidly backward and uniting very gradu-
ally with the gently curved basal margin. Posterior end truncated, straightened,
forming nearly a right angle with the hinge line, and one of from 75° to 80° with
the ventral edge. Hscutcheon narrow, not extending anterior to the beaks. In casts
of the interior, the internal cartilage support leaves two narrow impressions, one on
each side of the posterior half of the hinge line. Dentition of hinge not observed.
Muscular scars very faint.

Dimensions of a large cast of the interior: Greatest hight, 13 mm.; greatest
convexity (near center of shell), 15 mm.; length from beaks to postero-basal angle,
19 mm.; length from anterior extremity to upper portion of posterior margin, 15 mm.
In a smal] specimen only 6 mm. high, the other dimensions are in proportion, except
that the convexity is comparatively less.

This species is closely related to W. scofieldi, but may be distinguished by its
smaller size, greater convexity, truncated posterior end, shorter anterior end and
more pronounced postero-ventral angle.

Formation and locality.—Galena shales, Goodhue county, Minnesota.

WHITELLA SUBCARINATA, 2. Sp.
PLATE XLI, FIGS, 22 and ?23.
This species is in many respects like W. truncata, but is readily distinguished by
its lesser gibbosity, smaller beaks and more rounded shape.’ The umbonal ridge is

LAMELLIBRA NCHIATA. Die

Whitella ventricosa.]

angular or sharply rounded and distinct quite to the postero-basal margin. An
obscure furrow in the middle of the fat cardinal slope. From JW. ventricosa Hall, sp.,
which seems to be its nearest congener, it differs principally in the greater sharpness
and prominence of the umbonal ridge. The anterior end is much too small and
short for W. rugatina, W. concentrica and W. scofieldi. In each case other differences
might be mentioned, but those selected will, it is believed, suffice.

Greatest length, 23 mm.; distance from beaks to posterior extremity, 22.5 mm.;
posterior hight, 16.5 mm.; thickness, 13 mm. Antero-ventral—postero-cardinal diam-
eter, 17 mm.

Figure 23 is taken from a doubtful left valve, obtained from the lower Trenton
in Jo Daviess county, Illinois. As viewed now, this specimen represents an ancestral
form or variety of the present species from which also W. ventricosa, W. truncata and
perhaps other species as well have been evolved. More and better material, however,
is necessary before such a view of its relations can be consdered either as proved or
disproved.

Formation and locality.—The typical form is from the middle Galena near Wykoff, Minnesota.

Wauiretia ventricosa Hall.
PLATE XLI, FIGS. 24—26.

Edmondia ventricosa HALL, 1847. Pal. N. Y., vol. 1, p. 155.

Not Palearca ventricosa, HALL, 1859. Pal. N. Y., vol. iii, p. 271, and Twelfth Rep. State Cab.,

pp. 10, 68 and 95. (?=—Cyrtodonta huronensis BILLINGS.)

Not Cypricardites ventricosus HALL, 1862. Geol. Rep. Wis., vol. 1, p 438; nor WHITFIELD, 1882.

Geol. Rep. Wis., vol. iv, p. 209. (=Cyrtodonta, sp., undet.)

Believing that this species is represented among the undetermined fragmentary
shells from Minnesota, I thought it well to give illustrations of authentic specimens
from the Trenton of New York. These were received in an exchange some time
ago. Quite recently I sent two of them to Prof. R. P. Whitfield, of the American
Museum of Natural History, who compared them with the original types of the
species and verified the identification.

An examination of the New York examples established what I had already
suspected from the original figures, namely, that the species is a true Whitella and
not, as is commonly believed, a Cypricardites or Cyrtodonta. Its place in the genus
will be seen at once, when compared with other species of the genus figured on
plates xu and xu. The shell was thin, the beaks were full and prominent, the
umbonal ridge, though not as sharply defined as in many other species of the genus,
is still a more conspicuous feature than in any species of Cyrtodonta, the hinge has a
narrow external ligamental area or escutcheon, and ridge-like supports for a posterior
internal ligament, but no posterior lateral teeth. In short, the species presents

574 THE PALEONTOLOGY OF MINNESOTA.
[Whitella precipta.

every essential characteristic of the genus Whitella. We cannot, however, say this
of the specimens which were referred to the species by Hall in 1859 and 1862, and
Whithfield in 1882, since in these cases we are dealing with inequivocal types of
Cyrtodonta. The interior figured by Hall in vol. iii, Pal. N. Y.,as Palearea ventricosa,
is very different from the original Edmondia (now Whitella) ventricosa. That shell
seems to belong to the species previously described by Billings as Cyrtodonta sub-
carinata. The cast figured by Whitfield, if correctly represented, belongs to a species
of Cyrtodonta as yet unknown to me. In his description, however, he included the
species which I have named and described on page 537 as Cyrtodonta janesvillensis,

Comparing W. ventricosa with other species of the genus, W. swbcarinata will be
found to have a sharper and more prominent umbonal ridge. In W. rugatina and
W. concentrica the anterior end is much larger; W. precipta is much narrower poste-
riorly and a more elongate shell.

Formation and locality.—In New York the species occurs in the Trenton limestone at Watertown,
Middleville and other localities. If it really occurs in Minnesota, it will be, I think, in the middle
Galena of Goodhue and Fillmore counties.

WHITELLA pPRaorpera Ulrich.
PLATE XLI, FIGS. 15 and 16.

Whitella precipta ULRicH, 1890. Amer. Geol., vol. vi, p. 386; more fully described and figured in
1892, Nineteenth Ann. Rep. Geol. and Nat. Hist. Sur. Minn., p. 246.

Shell of medium size, ventricose, very oblique, elongate-ovate or subrhomboidal
in a side view, produced and sharply rounded in the postero-basal region. Beaks of
moderate size, prominent, strongly incurved; umbones full; umbonal ridge well
marked, traceable almost to the posterior extremity. Anterior end small, short,
narrowly rounded; ventral margin gently convex; posterior end produced and
narrowly rounded in the lower part; from’ the point of greatest extension to the
posterior side of the projecting umbones the outline is gently and almost uniformly
convex. Hinge line comparatively short, its length less than half the length of the
shell, the edge inflected to form a distinct escutcheon, extending somewhat in front
of the beaks. In casts of the interior the internal ligament supports have left
distinct impressions of unusual width on each side and behind the impression pro-
duced by the escutcheon. An obscurely defined ridge and sulcus is also to be seen
running through the middle of the cardinal slope. Anterior muscular scar faint,
subovate, acuminate below, situated very near the anterior extremity. Pallial line
represented by a thin raised line running parallel with the margin of the cast.

This species is very similar to IW. obliquata Ulrich, from the upper beds of the
Cincinnati group, yet I do not doubt that they are really quite distinct species.
That species grows to a larger size, is less elongate, wider posteriorly and with the

Oo
~)
[obra |

LAMELLIBRANCHIATA
?Megalodontidwz.]

umbones less tumid and not so prominent. The impressions of the internal liga-
ment supports also are very much less distinct. W. subcarinata is not so oblique,
shorter and has a longer hinge and narrower escutcheon.

Formation and locality—Galena shales near Cannon Falls, Minnesota.

Family 7? MEGALODONTID A, Zittel.
Genus PLETHOCARDIA, Ulrich.
Plethocardia, ULricu, 1892. Nineteenth Ann. Rep. Geol. and Nat. Hist. Sur. Minn., p. 243.

Shell thin, inequilateral, oblique, tumid, with margins closed; beaks large,
prominent, spirally enrolled and curving forward. [Posterior cardinal margin with
a narrow escutcheon or lunette. A strong and large process projects forward and
downward from the underside of the hinge just beneath the beak in each valve; one
strong linear lateral tooth, or thickened internal cartilage support, beneath the
posterior extremity of the hinge line and close to the margin. Anterior muscular
scar strongly impressed, situated in the antero-dorsal angle, margined on the inner
side by a curved ridge extending from the under side of the cardinal process. In
_ casts of the interior the filling of the anterior impressions forms a small but sharply
defined lobe. Posterior muscular scars indistinct, much larger than the anterior,
situated just behind the center of the postero-cardinal slope. Pallial line simple,
submarginal, faintly impressed.

Type: P.umbonata Ulrich. :

In the original description of this genus and of the typical species, I called the
subrostral process a cardinal tooth. This view I now believe to be at variance with
the facts, for the reason that the supposed tooth does not project beyond the plane
of the margins of the valve and therefore could not have interlocked with a corres-
ponding tooth or teeth in the opposite valve. In the left valve, upon which the
genus and P. umbonata was established, this process was somewhat injured in clear-
ing away the adhering matrix. It is, however, sufficiently preserved to show that
it had one large transverse depression in the lower part (for which reason it was
described as bifid) and probably one or two in the upper part. In an imperfect right
valve, recently obtained from Kentucky, the process is similarly marked with a large
depression in the lower part and two (perhaps three) smaller prominences above.
In neither specimen are the upper prominences in a sufficiently good state of pres-
ervation to admit of positive declarations respecting their character and purpose.
Still it is reasonable to suppose that they represent hinge teeth perhaps similar to
those of Whitella, especially since they lie just within the line of the hinge. As to the
lower part of the process, why should it not have supported an internal cartilage?

576 THE PALEONTOLOGY OF MINNESOTA.

(Plethocardia umbonata.

The shells of this genus present considerable external resemblance to those
of Whitella, Ulrich. As a rule they will probably prove shorter, more erect and
comparatively more ventricose. I believe also that Whitella offers closer affinities
than any other genus yet known, and I can see that it may prove difficult in some
cases to distinguish species of the two genera when the internal characters are not
available. Of course such difficulties cannot obtain when the diagnostic characters
of the hinge are preserved, since the strong subrostral process of Plethocardia is too
marked a feature to be overlooked in comparing the two genera. Good casts of the
interior even are easily distinguished by the presence of the small lobe beneath and
in front of the beaks of Plethocardia, the muscular impressions being very much less
distinct in the casts of Whitella. In the posterior part of the. hinge, however, as
well as in other respects, the two genera are practically the same.

It seems to me more than doubtful that Plethocardia belongs to the family
Megalodontide. A general resemblance to those heavy and strongly-hinged Devonian
and Triassic shells, which are included in the family by Zittel, may at first strike
one, but a critical comparison brings out too many important differences. I adopted
the above provisional arrangement chiefly that attention may be directed to the
genus as a possible progenitor of a remarkable family of shells. ~*

PLETHOCARDIA umBoNATA Ulyich.
o
PLATE XL, FIGS. 22—24,

Plethocardia umbonata ULRICH, 1892. Nineteenth Ann. Rep. Geol. and Nat. Hist. Sur. Minn., p. 244.

Shell about 25 mm. in length, strongly ventricose, obliquely subovate in a side
view, widest posteriorly; beaks large, very prominent, inrolled; umbonal ridge angu-
lar, traceable to the postero-basal margin; cardinal slope narrow, rather sharply
defined, concave. Anterior end very short, nearly ventrical, sharply rounded above;
dorsal margin arcuate, graduating into the posterior curve; the latter is produced
slightly in the lower part and accelerated as it turns into the broadly convex ventral
margin. Surface marked with concentric lines of growth, some of them strong.

Escutcheon narrow, extending backward from the beaks nearly to the posterior
extremity of the hinge. Subrostral cardinal process large, projecting obliquely for-
ward from the lower side of the hinge, with one large depression (? internal cartilage
pit) in the lower half and several smaller ones (? teeth sockets) above. A strong,
ridge-like thickening of the shell, probably representing either a postero-lateral
tooth or the support of an internal ligament, occurs just within the postero-cardinal
margin. Anterior adductor muscular scar situated in a cup-like depression formed
by a curved ridge which proceeds from the under side of the cardinal process and

LAMELLIBRANCHIATA. DEC

Plethocardia suberecta.]

the antero-cardinal margin of the shell; posterior scar indistinct, larger than the
anterior, situated a short distance beneath the post-cardinal margin. Pallial line
faint, simple, submarginal.

It is possible that this species is not distinct from the Cyrtodonta cordiformis of
Billings. His figures of that species looks so much like the shell above described
that I am nearly satisfied that they must be congeneric at least. It might be a
Whitella, but it is not a true Cypricardites. Compared with P. wmbonata it appears
that in the Canadian shell the beaks are situated farther back from the anterior
extremity, the umbonal ridge is rounded instead of angular and the outline different,
especially that of the posterior end, which is also wider.

Formation and locality.—Upper part of the middle third of the Trenton shales six miles south
of Cannon Falls, Minnesota. Also in cherty limestones of -the age of the Black River limestone of
New York, in Mercer county, Kentucky.

PLeTHOCARDIA SUBERECTA Ulyich.
PLATE XL, FIGS. 25—27.

Plethocardia suberecta ULRICH, 1892. Nineteenth Ann. Rep. Geol. and Nat. Hist. Sur. Minn., p. 245.

Shell small, but little oblique, exceedingly ventricose, short, subelliptical in a
side view, with the dorso-ventral diameter much the longest. Beaks very prominent,
large, strongly incurved, nearly terminal; umbonal ridge strong, sharply rounded,
with the cardinal and posterior slopes very abrupt and nearly flat. Anterior end
very short, the part in front of the beaks of casts consisting chiefly of the sharply
defined lobe-like filling of the anterior muscular impressions. Anterior and poste-
rior margins gently convex, subparallel; ventral edge sharply rounded. Hinge line
short, scarcely extending posterior to the umbonal ridge, as seen in a side view. In
the casts there is a depression beneath each beak that is prolonged on each side
around the muscular scar. The escutcheon seems to have been narrow, but the
internal ligament supports at the posterior end of the hinge line have left two
strong grooves, one on each side.

This species, though clearly congenerie with P. wmbonata, is so readily distin-
guished that comparisons are unnecessary.

Formation and locality.—Galena shales near Cannon Falls, Minnesota.

575 THE PALEONTOLOGY OF MINNESOTA. eae
LNuculide.

Family NUCULID..
Genus CTENODONTA, Salter.

Nucula, HALL, 1843. Geol. Rep. Fourth Dist. N. Y., p. 76; Amer. Jour. Sci., vol. xLvin, p. 292;

1847, Pal. N. Y., vol. 1, pp. 150 and 316.
Lyrodesma (part.), HALL, 1847. Pal. N. Y., vol. 1, p. 302.

Tellinomya, HALL, 1847. Pal. N. Y., vol. 1, p. 151; 1857, Tenth Ann. Rep. Reg. Univ. N. Y., p. 181:
also of the majority of American paleontologists since that date.
(Not Tellinomya, the correct form of Tellimya, BROWN, 1827, as given
by AGASsIz in 1846 in his ‘‘ Nomenclator Zoologicus.’’)

Ctenodonta, SALTER, 1851. Rep. Brit. Assoc., p. 36; 1859, Can. Org. Rem., Decade i, p. 34.

Palewoconcha, 8S. A. MILLER, 1889. North Amer, Geol. and Pal., p. 498.

Shell equivalve, closed, usually largest anteriorly,* occasionally subequilateral,
with the beaks situated sometimes behind the middle, but usually more or less in
front of that point; surface marked by concentric lines of growth; beaks approxi-
mate, generally small and never very prominent. Ligament external, rather small,
situated immediately behind the beaks; no striated area nor internal cartilage pit.
Hinge more or less arcuate, sometimes very gently, at other times bent almost at a
right angle; with series of small curved or geniculated transverse teeth, which
diminish in size more or less gradually from the extremities to the beaks; the
series are continuous and gradually pass into each other in the typical section of
the genus, but in other sections they are often interrupted beneath the beaks.
Adductor muscular impressions two in each valve, subequal, nearly always readily
distinguishable, and sometimes very deeply impressed, situated just beneath the
anterior and posterior extremities of the hinge; scars of small foot-muscles have
been observed in a number of species, one immediately above or in front of each of
the adductor scars; pallial line indistinct, simple, submarginal.

Type: C. (Tellinomya) nasuta Hall.

Several reasons have operated in the rejection of Hall’s earlier name Tellinomya
in favor of Salter’s Ctenodonta. First among these is the fact that Tellinomya was
used for a totally different group of shells at least one year previous to the date of
publication of the first volume of Hall’s Paleontology of the state of New York,
namely, in 1846 by Agassiz, in his “Nomenclator Zoologicus,” when he catalogued
the correct form of the incorrectly constructed generic name Tellimya, which had
been proposed by Brown in 1827. Believing that such corrections are allowable, |
am obliged to hold that Tellinomya, Hall, cannot stand under the rule relating to

*It is quite difficult to establish which is the anterior end in these shells. For the sake of uniformity I have, in
each case, assumed that the higher end (it is usually also the rounder) is the anterior. It may be well to state, moreover,
that I am not at all satisfied that this rule should apply in the C. recurva section of the genus, nor that Salter, Meek and
Worthen, Hall and others who have described species of that section, are right in assuming that the side toward which
the beaks are turned is the posterior. Though I have followed these authorities, I have done so chiefly bee: wuse it seemed
desirable, at any rate until the genus was worked up monographieally, to bave our descriptions as uniform as possiple.
Had I followed my own inclination it would have been to reverse, in this case, the present application of anterior and
posterior, upon the ground that the external ligament was situated upon the covex half of the hinge instead of the con-
cave, That this is reaily a fact is, I believe, conclusively shown in C. recurva. (See plate xnar, fig. 101.)

LAMELLIBRANCHIATA. 579

Nuculida.]}

preoccupied names. Salter objected to the adoption of Hall’s name, because it was
inappropriate and conveyed “an entirely erroneous view of the affinities.” This of
itself certainly would not be sufficient to invalidate the name, yet some weight
attaches to it when considered in connection with other defects. Salter justly
observes that “the chief characters of the genus reside in the hinge and teeth,
which are neither figured nor described by him (Hall), casts only of the interior and
external surface having been given in the plates of his excellent work, nor was the
external ligament observed.”’ This is all strictly true and, what is more, it is scarcely
to be doubted that if Hall had observed the nuculoid character of the hinge he would
not have proposed Tellinomya. He would have placed the species under Nucula or
possibly Lyrodesma, that being the arrangement adopted by him in all cases where
he did see the ctenodontoid hinge. Nor can we doubt that Ctenodonta was acceptably
described at least five years before Tellinomya, Hall, was redefined in accordance
with the true character of the shells upon which the genus was founded originally.
Finally, the original description of Tellinomya was so totally at variance with the
facts that Salter could not for a moment be blamed for failing to recognize the
identity of 7. nasuta and the shell which he proposed to call Ctenodonta.

Taking all these defects of Tellinomya into consideration, I do not see how we
can do otherwise than adopt Ctenodonta in preference to Hall’s name. Had Tellin-
omya not been preoccupied I would have suggested another solution of the difficulty,
namely, to subdivide the genus so that both names might be used, at least provision-
ally, Tellinomya for the typical group of species and Ctenodonta for the higher and
round or subtriangular forms like C. astartiformis Salter. But being preoccupied,
there is no room for Tellinomya in this connection.

Taken as a whole, the genus Ctenodonta is a remarkably complex group of
species. This may perhaps be accounted for by the great number of the recog-
nizable forms, yet it is more likely the result of too great an expansion of the
generic limits. Indeed, the variety of characters exhibited in the genus as now
accepted is so great that it is difficult to draw up a satisfactory description without
becoming unusually circumstantial. Thus, there are elongate shells and others in
which the length is exceeded by the hight. In many the outline is elliptical, in some
subrhomboidal, in others rounded and in a few subtriangular. In some the umbones
are compratively large and full, in others very small, and the beaks may be turned
either forward or backward. Internally the structure is equally diverse. The hinge
plate may be narrow or broad, nearly straight or bent rectangularly, and with out-
wardly or inwardly bent denticles. The latter, though always smallest near the
beaks, may form a continuous series from one end of the hinge to the other, or the
continuity of the series may be interrupted beneath the beak. This interruption

580. THE PALEONTOLOGY OF MINNESOTA.
[Nuculida

may be produced, without materially affecting the arrangement of the teeth, by the
development of a small pit immediately beneath the beak (see plate XLII, fig. 80),
or the teeth may be so arranged that the two series of teeth are directed at almost
right angles to each other (see plate XLII, figs. 39, 90, 101 and 102). Finally, the
shell is often very thin and the muscular scars barely distinguishable, while in other
forms the shell may be thick and the muscular imprints exceedingly strong.

In the present work I have allowed all these divergent types to remain under
the single genus Ctenodonta. This does not, however, say that 1 could not have sub-
divided the genus into several, nor that I do not believe that such a course will
eventually be considered not only possible but desirable. Meek and Worthen long
ago” expressed themselves as favoring a separation of the subtriangular forms like
C. alta Hall, from the more typical ovate or elongate species. And Dr. S. A. Miller}
quite recently proposed the new genus Palwoconcha for one of the species of that
group. He did so, however, under the misapprehension that the hinge of the species .
described by him is edentulous; so his evidence on the point is much weakened, for he
would, most likely, not have proposed his genus had he understood the hinge fully.

For the reason about to be mentioned, I am probably in a better position than
any one else to speak of the possible subdivisions of this genus, namely, my efforts
to collect a large mass of material have been successful, not only in the way of
individuals, but in adding very greatly to the number of known species. Indeed,
the Lower Silurian species in my cabinet outnumber the forms described previous
to 1890 more than two to one. I believe, therefore, that with the careful study that
has been given to this abundance of material, I am able to discriminate in a fairly
trustworthy manner between the important and unimportant characters, to approx-
imate truth in my views of the inter-relations of the species and to understand some
of the genetic questions involved in the development of the family.

The Lower Silurian species may be arranged in six more or less well marked
groups, as follows:

I. C. nasuta group.

Elongate shells, narrow posteriorly, beaks subcentral; muscular scars moder-
ately or distinctly impressed, hinge but slightly arcuate, teeth in a continuous
series, straight or bent outwards.

Species: mnasuta Hall, nasuta, var. robusta Ulrich, swbnasuta Ulrich, oviformis Ulrich,
cuneiformis Ulrich, regia, n. sp., ttennesseensis, n. sp., appressa, n. sp., crandalli,
n. sp., iphigenia Billings.

*Geol. Sur. IIl., vol. iii, p. 309; 1868.

+North American Geology and Paleontology, p. 498; 1891.

%The new species, which are not described in this work nor in vol. vii of the Ohio Geological Survey reports, are
marked simplyvas.n.’sp. Descriptions of these forms will, it is hoped, be published at an early date, the plate on which
they are illustrated being ready for publication,

LAMELLIBRANCHIATA. 581

Nuculide.]
Il. C. gibberula group.

Shells usually short, thick, with very strongly defined muscular impressions;
hinge strongly bent, with the series of denticles interrupted beneath the beaks;
teeth straight or curving outward.

Species: gibberula Salter, contracta Salter, angela Billings, carinata Ulrich, planodor-
sata Ulrich, longa Ulrich.

Ili. C. levata group.

Shells usually of ovate form, rather thin, with muscular scars moderately dis-
tinct; denticles converging inward, forming a continuous series in}the Trenton
species. In the Hudson River forms, however, the series is more or less interrupted
by the development of a small and undefined pit just beneath the beak.

Species: Jevata Hall, donaciformis Hall, abrupta Billings, nitida Ulrich, medialis Ulrich,
scofieldi Ulrich, socialis Ulrich, hartsvillensis Safford, danvillensis, n. sp., retrosa
Ulrich, filistriata Ulrich, albertina Ulrich, simulatrix Ulrich, tumida, n. sp.,
madisonensis Ulrich, fecunda Hall, calvin Ulrich, mundula, n. sp., perminuta
Ulrich, nunculiformis Hall, ? hilli Miller.

IV. C. pectunculoides group.

Shells subcircular, compressed-convex, beaks very small; hinge plate strong,
regularly arcuate; teeth in a continuous series. /
Species: subrotunda Ulrich, circularis, n. sp., pectunculoides Hall, cingulata Ulrich,
pulchella Hall.

V. C. recurva group.

Shells high, the lower half semicircular, the upper subtriangular; hinge plate
rather strong, bent at nearly a right angle, the (?) anterior part convex, the (?)
posterior concave; denticles in two distinct series, arranged transversely on the
plate and therefore at widely different angles on the two. parts of the hinge.
Species: compressa Ulrich, arstartiformis Salter, intermedia Ulrich, alta Hall, obliqua

Hall.
VI. C. logani group.

Thin gibbous shells, with subcentral large beaks; muscular sears faint: —
but little arcuate, the denticles in continuous series, bent inward.
Species: Jlogani Salter, dubia Hall, gibbosa Hall, ? ovata Hall.

Group I, the typical section of the genus, seems to be strictly confined to Lower
Silurian deposits and embraces the largest known representatives of the family
Nuculide. Group II appears to be even more restricted in its range, being unknown

582 THE PALEONTOLOGY OF MINNESOTA.

LNuculide.

above the top of the Trenton. Group III is by far the largest section of the genus
both in its specific and individual development. It may justly be called the nuculoid
section, since not only the general expression of the shell is decidedly like Nucula,
but its internal characters likewise approach those of that remarkably persistent
type more closely than is the case with any of the other groups here defined. I
think that the evidence indicates very strongly that Nucula was developed from this
stock. As is well known, that genus is distinguished from Ctenodonta chiefly in
having a small but well defined internal cartilage pit immediately beneath the
beaks. Now, although in the Trenton forms of Group III the hinge denticles form
a perfectly continuous series, this cannot be said of the Hudson River species. In
many, if not all, of these, namely, the series of teeth are more or less distinctly
interrupted beneath the beaks by the incipient development of an at least similar
pit. So far as it is possible to say, true species of Nucula occur in the Devonian, so
it is but natural to assume that the missing links between them and the Ctenodonta
levata group of species are to be found in the intervening Upper Silurian deposits.
But here we meet with an obstacle in the fact that none of the Upper Silurian shells
that have been referred to Ctenodonta (Tellinomya) and Nucula*, with the possible
exception of Tellinomya curta Hall, of the Clinton group, belong to the C. levata
section. It does not, however, follow that such species did not exist, though we
must admit that it is a strange, if not a significant fact that they have not yet been
found. Still, the significance of their absence is lessened when we consider that the
Upper Silurian deposits throughout are relatively poor in remains of Lamellibran-
chiata. It is also to be remarked that the forms which have occurred belong chiefly ©
to families widely different from the Nuculidw. It is possible that the Devonian
genera Palwoneilo and Nuculites also came from this stock, such a development being
faintly indicated by C. fecunda and C. nuculiformis; but taking all the characters
into consideration, and the direction of the variation that may be followed into the
lower divisions of the Upper Silurian, Clidophorus seems to me a more likely ancestor
for those genera.

Group IV may be a departure from the C. recurva group, but, as it seems to me
to be a more primitive type, I would rather consider the relation as reversed. The
only objection to the latter arrangement may be removed at any time, since it is
nothing more than that C. compressa, a typical species of the recurva group, has been
found somewhat lower in the Trenton formation than the earliest known member
of the pectunculoides group.

*Very little is known of the hinge of the Up. Sil. species that have been referred to Tellinomya by Hall and others.
so that we are justified in doubting that they really belong to the genus. Those known to possess a denticulated hinge
are much more like Palwoneilo than Ctenodonta.

LAMELLIBRANCHIATA. DSS
Nueulide.]

Group V is probably the most distinct of all these sections. It is certainly the
least variable and the easiest to recognize, the Astarte-like form of the shells alone
being sufficiently diagnostic. The subrostral interruption of the hinge denticles is
very distinct and the point is often marked by a sort of pit, quite undefined, however,
that may have lodged an internal cartilage. Nucula may really have been evolved
from this type, since it would have required but a slight modification of the hinge,
a depression or lengthening of the form, and a filling of the umbones. As it is,
C. recurva is nearer Nucula than it is to C. nasuta, but several species of the levata
section approximate that genus even more closely, so that we are obliged to regard
the balance of the evidence to be in favor of the levata group, unless both the
groups have contributed to make Nucula as now understood.

Of Group VI only C. logani is well known, so we cannot say much about aftfin-
ities. ‘The species are all Trenton, and their general aspect is quite different from
the other groups.

It is an interesting fact that all of these sections are represented already in the
lowest geological division (considering the Birdseye and Black River limestones as one)
in which the genus makes its first known appearance; the nasuta group with the species
lennesseensis and nasuta, the gibberwla group by all of its species except C. carinata,
the levata group by at least five species, the petunculoides group by the species
subrotunda, the recurva group by C. compressa, and the sixth group by C. logani.
Kach group again is as sharply marked in these first species as it is at any subse-
quent time; nor have we any evidence to aid us in deciding which of the six groups
is the most like the primitive stock. It is evident, therefore, that a long line of
forms of this type must have existed in the ages preceding the Birdseye of which we
now have no knowledge whatever. The same remarks apply almost equally well
to the other families of Lamellibranchiata, and one of the most remarkable facts in
paleontology is the almost total absence of the class in the Calciferous, especially
when we consider that that formation abounds in Gastropoda and Cephalopoda.

I have carried on a number of very interesting comparisons between the species
of Ctenodonta and certain forms of recent genera like Nezlo; Malletia and Sarepta, three
nuculoid genera, and Axinwa and other Arcidw. If this work was not already growing
beyond the limits alloted to it, I would gladly give the results of these comparisons
here fully, but under the circumstances I am obliged to restrict myself to a few
general remarks. The three nuculoid genera mentioned are very similar indeed to
the C. nasuta group of species, the first and second differing chiefly in having a sinu-
ated pallial line, while the third has an internal cartilage pit beneath the beaks like
Nucula. Certain Cretaceous species of Avxinwa (€. g. A. sulplanata Stoliczka) are strik-
ingly similar to the C. pectunculoides section, the only difference of real consequence

584 THE PALEONTOLOGY OF MINNESOTA.

(Ctenodonta nasuta.

being the presence of a low triangular striated area between the beaks and the hinge
in the Avinea, Other Arcide present almost equally close resemblances to. logani.
Aside from the ligamental area the principal characters of Arca and Isoarca are
practically the same as in one or another species of Ctenodonta.

We have then three families of recent shells (as defined by Stoliczka) any one or
all of which, and I believe it is the latter, may have been derived from this early type.

C. nasuta section.

Crmnoponta nasuta Hall.
PLATE XLII, FIG. 30.

Tellinomya nasuta HALL, 1847. Pal. N. Y., vol. 1, p, 152; 1857, Tenth Rep’t. Reg. Uniy. N. Y.,
p. 1838, ?fig. 2. (Figures 1 and 3 not strictly nasuta,)

Ctenodonta logani SALTER, 1851. British Asso. Rep., p. 63. (Not C. logani Salter, 1859.)

Isoarca logani WooDWARD. Manuel Shells, p. 269.

Ctenodonta nasuta SALTER, 1859. Can. Organic Remains, Dec. I, p. 35.

Shells transversely elongate subovate, the length one-twentieth or more greater
than twice the greatest hight; beaks rather small, not very prominent, incurved,
situated about one-twelfth of the entire length in front of the middle; anterior end
large, broadly and regularly rounded; posterior end produced, tapering, rather nar-
rowly rounded at the extremity; cardinal margin nearly straight, basal line broadly
convex except for some distance behind the middle where it is straight or more
often gently sinuate. Greatest thickness near the middle of the anterior half,
equalling about one-third of the length of the shell. Umbones moderately inflated,
the posterior cardinal slope defined by an obscure umbonal ridge, very abrupt for a
short distance behind the beaks, more so than on the anterior side; a broad and very
shallow sulcus crosses the valves obliquely from the umbones to the contraction in
the base. Ligament attached in a sharply defined groove on each side of the hinge
line, extending from the beaks about one-third of the distance to the posterior
extremity. Surface marked with obscure concentric lines.

The test being thin, casts of the anterior look much like the exterior of the shell
itself. The muscular scars are faintlyimpressed and usually determined with difticulty
on all except the largest casts. The denticulated part of the hinge is comparatively
short, being but 21 mm. in length in a specimen 56 mm. long. Its upper margin is
nearly straight, but the lower side is rather distinctly biconvex, the plate being con-
stricted beneath the beaks to little more than half of its width on each side. The
denticles form a continuous series, are small and vertical beneath the beaks, slightly
oblique in front of them, and strongly curved outwards behind them. The entire
series, so far as observed, contains twenty-seven to twenty-nine teeth, divided almost
equally with respect to the beak.

LAMELLIBRANCHIATA. 58)

Ctenodonta subnasuta.]

None of the northwestern specimens of this species seen by me quite reach a
length of 40 mm., the average beiug about 25 mm. In Canada they grew to much
greater size, some of the specimens from Pauquette’s Rapids on the Ottawa river
having a length of more than 60 mm.

Associated with this species in Wisconsin and at Pauquett’s Rapids there is a
form which, though it has been identified unreservedly with C. nasuta by Hall and
others, I find to be not strictly identical with that species. The anterior end is higher
and larger, and the posterior end shorter, so that the beaks, instead of being in front
of the midlength, are a trifle behind that point, the muscular impressions are deeper,
and the hinge plate is on the whole narrower and much less constricted in the mid-
dle. This form, for which I propose the varietal designation robusta, was figured by
Prof. Hall in the Tenth Annual Report of the Regents of the University of New York
on page 183 as Tellinomay nasuta. He figures two specimens of which the smaller
may belong to nasuta. The larger example, however (figures | and 3), I refer to the
variety robusta, and I do so with the utmost confidence, the specimen being in my
possession at this moment. At Pauquette’s Rapids the variety attains about the
same size as the typical form of species, but in Wisconsin it is much the larger.

Near the top of the Trenton in Kentucky there is a form, that I shall call C. regia,
which seems to represent the culmination of the differentiation begun in the variety
robusta. In this Kentucky species the hight is even a trifle greater, the base is not
sinuate, the muscular scars are very deep, and the hinge plate stronger than in both
the variety and the typical form of nasuta.

7

Formation and locality.—C. nasuta occurs sparingly in the lower Trenton limestone at Minneapolis
and in the middle third of the Trenton shales in Goodhue county, Minnesota. In Wisconsin the species
is more abundant in the ‘‘ Lower Blue” and the ‘“‘ Upper Buff” limestones at Beloit, Janesville and Min-
eral Point. It has also been found in the same beds at Dixon and other localities in Illinois. In Canada
it occurs in the Black River and Trenton limestones at Ottawa and numerous other points. The original
- types of the species came from the Trenton limestone at Middleville and Trenton Falls, New York, aud
it is catalogued by Prof. J. M. Safford among the fossils of his ‘‘ Central,’ ‘‘Glade” and ‘‘ Carter’s Creek ”
limestones in Tennessee. Variety robusta occurs at Pauquette’s Rapids near Ottawa, Canada, and in the

“Upper Buff” limestone at Beloit, Wisconsin.

Mus Reg. No. 8317; var. robusta, 8315.

CTENODONTA SUBNASUTA, 2. SP.
PLATE XLII, FIGS, 34—36.

This shell is no doubt closely related to C. nasuta, but, aside from its much
smaller dimensions, it differs in several particulars that have seemed of sufficient
importance to merit specific recognition. ‘Thus the posterior end is somewhat
longer, the beaks being placed farther in front of the middle, the anterior end is
more obtuse in a dorsal view, the beaks are turned anteriorly rather than backward,
the lower margin of the hinge plate is almost straight instead of biconvex, while

586 THE PALEONTOLOGY OF MINNESOTA.

[Ctenodonta oviformis.

the denticles are relatively more numerous on the posterior part, there being about
sixteen or seventeen on this side of the beaks to about ten in front of them. Casts
of C. nasuta again exhibit a rather well marked lanceolate depressed area extending
posteriorly from the beaks about half way to the extremity of the cast. In C. sub-
nasuta the corresponding area is not lanceolate, but consists of a furrow on each
side of the raised hinge line running backwards almost to the extremity. The fol-
lowing two species also are rather closely related, but are readily enough distin-
guished by their shorter form and lesser convexity.

Since the above was written, I have found among my unworked material from
the middle third of the Trenton shales in Goodhue county, two valves that may
represent an earlier form of this species. Artificial casts of the interior of these
valves closely resemble the Galena shales type of the species, the only difference
being that the central part of the casts is not quite so full and the basal line less
straightened in the posterior half. There is also a flattened rim along the ventral
border that is not seen in the type. In these features the valves remind somewhat
of C. oviformis, but they cannot belong to that species, since they are too narrow
posteriorly and have the beaks situated more anterior to the center. The hinge is
rather well preserved on both the valves, each having about twenty-six denticles,
nine of them in front of the beaks. Of the latter the anterior five are larger than
any of the others. The hinge, on the whole, resembles that of C. cunetformis, but
the anterior teeth are larger and the beaks situated farther forward.

Formation and locality—The type is from the Galena shales near Cannon Falls, Minnesota.

CTENODONTA OVIFORMIS, 2. Sp.

PLATE XLII, FIG. 29.

Shell small, compressed convex, transversely ovate, the ends rather narrowly
_ rounded, subequal, the anterior a trifle wider and shorter than the posterior, the
base almost regularly convex, the hinge line gently arcuate, and the beaks rather
small, scarcely prominent and situated slightly in front of the midlength. Muscular
scars comparatively distinct. Number of teeth and surface unknown, but the cast
is marked with several obscure concentric furrows. Length, 9.2 mm.; hight about
6 mm.; thickness, 3.8 mm. P

This small shell is relatively shorter, less produced and wider posteriorly, and
more rounded in the basal outline than C. nasuta and C. subnasuta. Collectors will,
I think, find little trouble in recognizing it.

Formation and locality.—Galena shales, near Cannon Falls, Minnesota.

LAMELLIBRANCHIATA. 587

Ctenodonta cuneiformis.]

CTENODONTA CUNEIFORMIS, %. Sp.

PLATE XLII, FIGS. 31—3.

Shell small, compressed convex, transversely somewhat acuminate-ovate, tapering
posteriorly to a narrowly rounded extremity; anterior end shorter than the posterior,
but much higher and broadly rounded, except in the antero-cardinal region, where
the outline projects slightly beyond the path of a uniform curve; base rather prom-
inently rounded in the middle, convex throughout the anterior half, straight or very
faintly sinuate in the posterior half; beaks small, not prominent, situated about 4mm.
behind the anterior extremity in a specimen 11 mm. long; posteriorly from the beaks
the cardinal outline is straight, in front of them gently concave. Behind the center
the shell is more or less distinctly contracted. Surface with obscure concentric strie.
Hinge plate of moderate strength, comparatively long, very gently bent, and just
appreciably contracted beneath the beaks, with about twenty-seven nearly vertical
teeth in each valve, twelve in front of the beak. The posterior six or seven teeth are
stronger than the rest and bent inward. Test thin, muscular scars not observed. The
largest specimen seen, a right valve, is 12 mm. long, 7.4 mm. high and 1.5 mm. thick.

The contraction and narrowness of the posterior end gives to this species some-
what the appearance of C. contracta Salter, but the two species are really widely
different. The Canadian shell is higher, more convex and its cardinal outline much
more angular, the hinge plate strongly bent and very narrow under the beaks, the
teeth larger and not so numerous, and the shell much thicker. The affinities of
C. cuneiformis are probably with C. nasuta and C. subnasuta. The former, being a
much larger shell, is not likely to be confounded with it. The latter is narrower
anteriorly and wider posteriorly, is more convex, especially in a front view, its
posterior half is not contracted in the same manner, and the anterior outline more
uniformly rounded.

Formation and localityx—Four specimens were found at a point about six miles south of Cannon
Falls, Minnesota, where they occurred in the upper part of the middle third of the Trenton shales. The
same locality and bed has furnished numerous other Lamellibranchiata.

C. gibberula section.

CYrENODONTA GIBBERULA Sa/ter.
PLATE XLII, FIG. 37
Ctenodonta gibberula SALTER, 1857. Canadian Organic Remains, Dec. 1, p. 38.

Tellinomya ventricosa HALL, 1861. Rep. Supt. Geol. Sur. Wis., p. 27; 1862, Final Report of same,
p. 38, fig. 8; MEEK and WoRTHEN, 1868, Geol. Sur. Ill., vol. iii, p. 307.

Shell rhombic subovate, ventricose, the hight, length and thickness, respectively,
as seven, ten and six, with large incurved beaks, situated a little behind the mid-
length; antero-dorsal and ventral margins subparallel, the posterior end obliquely

588 THE PALEONTOLOGY OF MINNESOTA.

(Otenodonta gibberula.

truncate above the narrow and sharply rounded lower part; anterior end broadly
rounded and continuing into the basal margin; the latter is straight or very gently
sinuate and ascends from the prominently rounded anterior part; posterior umbonal
ridge inconspicuous in a lateral view, rather sharply defined, however, in a dorsal
view by a narrow furrow which outlines a wide lanceolate flattened area, equally
divided by the hinge line, and in the upper part of which (immediately behind the
beaks) the ligament is attached to distinct fulcra; anterior dorsal slope abruptly
rounded; entire anterior half of valves strongly ventricose, while between this part
and the posterior umbonal ridge a slight sulcus crosses from near the beak to the
base. Surface marked by rather distinct, closely arranged, subequal concentric strie
of growth, tending to irregularity in the basal parts of old shells.

Impressions of adductor muscles extremely deep, the anterior pair larger than
the posterior. A small, though distinct, pedal muscle scar is always present on the
upper part of the strong ridge which forms the inner boundary of the anterior
adductor, (in casts it lies at the bottom of the deep cavity produced by this ridge),
but the corresponding posterior scar is rarely distinguishable. Hinge plate very
narrow at the beaks, but widening rapidly on each side, the anterior half somewhat.
the stronger and slightly concave along its inner margin, both terminating abruptly
at the muscular scars; denticles twelve behind and ten or eleven in front, those
near the beaks very small, all interlocking deeply, especially those of the anterior
set, which are also somewhat larger than the posterior. The shell is very thick and
the rostral filling so considerable that in casts of the interior the beaks appear
obtuse and widely separated.

I have very carefully compared a large series of the northwestern form which
Hall named ventricosa with authentic Canandian examples of Salter’s C. gibberula,
and I can say, with perfect confidence, that there is not the slightest reason for con-
sidering them as distinct species. The only difference that Tecan detect is that the
northwestern specimens grow to a larger size than the Canadian. Tennessee speci-
mens also attain greater dimensions than the latter, though their average size
scarcely equals that of Wisconsin examples. Meek and Worthen suggested (op. cit.)
that Tellinomya ventricosa may be the same as C. contracta Salter, but in this they
were mistaken, since that species is certainly distinct and, so far as known, does not
occur at any of the northwestern localities.

Formation and locality—In Canada this species occurs in the Black River limestone at Pauquette’s
Rapids. In Tennessee it occupies an equivalent or lower position near Murfreesboro. In Wisconsin, at
Beloit, Janesville and Mineral Point, and at several localities in Illinois and Iowa, it forms one of the
most striking fossils of the limestones beneath the Galena, particularly the ‘‘Upper Buff.” In Minne-

a sota it seems to be a rare fossil, being, so far, known only from Minneapolis, where it occurs in the
Trenton limestone a few feet beneath the shales.

Mus. Reg. Nos. 8309, 8316, 8339.

LAMELLIBRANCHIATA. 589

Ctenodonta carinata.]

CTENODONTA CARINATA, 2. Sp.

PLATE XLII. FIGS. 41—43.

Shell rather small, gibbous in the anterior and rostral portions, the ends obtuse
in a dorsal view, the beaks large, prominent, strongly incurved, situated near the
midlength and turned decidedly toward the posterior end; the outline may be
described as subtriangular or obscurely quadrate; anterior margin most prominent
and strongly rounded in the lower half, the upper two-thirds more gently curved
and sloping backward to the beaks, being continuous with the antero-dorsal margin;
ventral margin straight or broadly sinuate, curving abruptly into the subtruncate
posterior margin and forming, with the latter, an angle of about 80°; cardinal out-
line distinctly concave behind the beaks; post-cardinal region slightly produced,
though too blunt to be called alate; posterior umbonal ridge prominent, angular,
extending to the post-ventral angle; point of greatest convexity on the rounded
anterior umbonal ridge; between the two ridges a wide, undefined sulcus, extending
from the umbones to the base. Surface marked with distinct and rather irregular
concentric lines of growth. Hinge plate arcuate, in other respects apparently as in
C. gibberula Salter. Shell thick, muscular scars not observed.

C, gibberula is the only shell known to me with which C. carinata might be
compared. Although imperfectly known, I am quite confident that its affinities lie
chiefly with that species. Still, though the resemblances are sufficient to prove that
the two forms belong to the same section of the genus, it is scarcely likely that any
one will fail to distinguish them specifically, the outline in the two species being
different in several respects. Thus, in C. carinata the posterior end is wider, the
post-cardinal region produced and subcuneate instead of flattened, the anterior
margin is more prominent below, and above curves more regularly into the dorsal
outline, while the basal margin is not so prominent anteriorly and on the whole
more nearly horizontal. The posterior umbonal ridge also is more prominent, the
mesial sulcus or flattening is a more pronounced feature and the anterior slope more
abrupt. Finally, the hinge plate is less bent and curved rather than geniculated.

Formation and locality.—Middle Galena, about one mile east of Fountain, Minnesota.

CrmnopontTa PLANODORSATA Ulrich.
PLATE XXXVII, FIGS. 25-28; PLATE XLII. FIGS. 38—40,
Tellinomya planodorsata ULRICH, 1892. Nineteeth Ann. Rep. Geol. and Nat. Hist. Sur. Minn., p. 217.
Shell small, moderately convex, subtriangular or trapezoidal, the hight, length

and thicknes, respectively, ten, fourteen and five mm.; beaks small, incurved, scarcely
projecting above the hinge, situated nearly one-third of the entire length from the

590 THE PALEONTOLOGY OF MINNESOTA.

[Ctenodonta longa.

anterior extremity. Posterior end long, subtriangular in outline, with the extremity,

subacute and the dorsal side almost straight (faintly convex) from the beaks backward;
ventral margin broadly rounded, semielliptical; anterior margin nicely rounded.
Post-cardinal side thick, with a large, sharply defined and slightly concave area
reaching from the beaks to near the posterior extremity of the shell. Surface gently
convex, scarcely sloping toward the postero-cardinal area, marked with exceedingly
fine concentric strize and a few stronger lines of growth. Hinge plate strong,
abruptly bent, the posterior part nearly twice as long as the anterior, the two
parts forming an angle of about 105°; denticles very little curved, in two distinct
series, those in each row sét transversely on the hinge plate, about eleven in the
anterior series and nineteen or twenty in the posterior series. Muscular impressions
very deep, bordered on their inner sides by strong ridges and set into the wide exca-
vated ends of the hinge plate; pallial line simple, faint, submarginal.

The interior of this strongly marked species proves to be quite different from
what I expected when I described it from the exterior alone. Instead of showing
relations to C. /evata, excellent valves since obtained prove the species to be nearer
C. gibberula and C. contracta, Still, C. planodorsata occupies a somewhat isolated posi-
tion. Inthe first place, casts of the interior, with their very prominent muscular scars,
remind at once of the present section of the genus. The hinge, however, is very
different from that of the typical members of the section, the plate being widest
under the beaks instead of much the narrowest, and the series of denticles very
abruptly divided into two sets, the whole hinge, therefore, being much more as in
the C. recurva section. C. longa has similar characters, as appears to be the case
also with an undescribed species from the Trenton of Tennessee, so that it might
have been well to institute another section of the genus. But as these sections are
merely temporary natural groupings of the species, pending a more thorough study
of the whole family, the ommission cannot be of much consequence.

The species is so easily recognized by the flat dorsum that comparisons are quite

unnecessary. :

Formation and locality.—In the upper part of the middle third of the Trenton shales at severa
localities in Goodhue county, Minnesota.
Crenoponta Lonea Ulrich.
PLATE XXXVII, FIGS. 30 and 31.
Tellinomya longa ULRIcH, 1892. Amer, Geol., vol, x, p. 103.
Shell small, compressed, elongate-elliptical, the length equalling a little more

than twice the greatest hight. Beaks small, situated about one-fourth of the entire
length from the anterior extremity. Cardinal line, on the whole, very slightly

LAMELLIBRANCHIATA. 59]

Ctenodonta logant.]

convex, straight behind the beaks; anterior end short, semicircular; ventral margin
gently convex; posterior end a little narrower than the anterior and more sharply
rounded. Surface with obscure concentric lines; sloping rapidly at the cardinal
margin, but very gently to the ends and ventral edge. Hinge plate of moderate
strength, bent a little beneath the beak and with a thickening on the lower side in
front of same. Posterior to the beak the plate is long, straight and bears twenty or
more small teeth, while on the anterior part only nine are to be counted. In the
vicinity of the beak the teeth, especially those on the posterioy side, are very small,
and as they are all set at right angles to the hinge plate, the continuity of the series
is interrupted where the two series come together. The interruption is easily over-
looked, because of the slight bend in the hinge plate. Anterior muscular impression
deep, situated immediately beneath the end of the hinge. Its posterior side is defined
by a strong vertical thickening of the shell, in the upper part of which the scar of a
small pedal muscle is to be observed. Posterior scar distinct, but less sharply
impressed than the anterior, situated at the end of the hinge just within the thin
post-cardinal border of the shell.

The characters of the hinge and the deep muscular impressions show that this
species is related to C. planodorsata, with which it is also associated in the shales.
There is, however, room for several intermediate species, the form being much more
elongate, the back not flattened, the posterior end rounded instead of subacute, and
the hinge much less bent. In C. subnasuta the shape is somewhat similar, but the
hinge is different, the muscular impression not nearly so distinct, the beaks larger
and situated farther from the anterior end, while the anterior half is relatively
higher.

Formation and locality.—Middle third of the Trenton shales, Goodhue county, Minnesota; asso-
ciated with C. planadorsata, C. compressa, C. socialis and C. scofieldi.

C. logani section.

CrENODONTA LOGANI Salter.
’ PLATE XLII. FIGS. 26—28.

Tellinomya dubia HALL, 1857. Tenth Ann. Rep. Reg. Univ. N. Y., p. 183, flgs 4 and 5. (Not

T. dubia Hall. 1847, Pal. N. Y., vol. 1, p. 153.)

Ctenodonta logani SALTER, 1859. Canadian Organic Remains, Dee. i, p. 26. (Not C. logani Salter,
1851, Rep. Brit. Assoc., p. 63, which proved to be the same as
Tellinomya nasuta Hall, 1847.)

Shell of the medium size, rather elongate, subovate, strongly convex, very gib-
bous in the umbonal region, with the strongly incurved beaks turned slightly forward
and situated near the midlength; posterior end a little the narrower, rounded, but
not quite uniformly, the lower part being usually a trifle prominent; basal margin

gently arcuate, the posterior half somewhat less convex than the anterior; anterior

592 THE PALEONTOLOGY OF MINNESOTA.

[Ctenodonta nitida.

end regularly rounded, or this is so only in the lower two-thirds, the curve of the
outline sometimes increasing in rapidity as it turns into the cardinal margin.
Posterior umbonal ridge prominently rounded; in front of it a very obscure mesial
sulcus; post-cardinal slope rather abrupt, with two obscure curved furrows, and in
the upper part the fulcra to which the external ligament was attached. Surface
marked by unequal concentric lines of growth. Hinge plate of moderate strength, —
gently arcuate, slightly contracted in the middle, 15 mm. long in a specimen 25 mm.
in length, bearing a continuous row of teeth curving strongly inward, the whole
number in each valve about seventeen, of which nine are posterior; as usual, the
central ones are the smallest. Shell comparatively thin; muscular impressions faint.

The gibbosity of the shell and the unusual prominence of the umbones removes
this species from the C. nasuta section, while the thinness of the test and the faint
delineation of the muscular scars will not allow it to be placed in the C. gibberula
section. The natural position of the species may, however, still be considered as
intermediate between those two sections.

Formation and locality.—‘‘ Upper Buff limestone” of the Trenton formation, Beloit, Wisconsin.
In Canada the species occurs in the Black River limestone at Pauquette’s Rapids, near Ottawa.
Mus. Reg. No. 8316—1.

C. levata section.
Crexpowra nitipa Ulrich.
PLATE XLII, FIGS. 44—47.

Tellinomya nitida ULRICH, 1892. Nineteenth Ann. Rep. Geol. and Nat. Hist. Sur. Minn., p. 215.

Shell small, thin, moderately ventricose, trapezoidal or somewhat obliquely sub-
triangular, the antero-cardinal region somewhat alated; umbones full, beaks small;
closely ineurved, directed slightly backward. Posterior extremity oblique, rather
abruptly truncated, flattened, nearly straight, pinched and projecting slightly beyond
the convex part of the shell in the upper half and narrowly rounded below. Ventral
margin gently convex, usually curving rather sharply upward at the ends. Anterior
end wide, rounded and most prominent in the lower half, straightened above, the
junction with the hinge-line subangular. Surface, excepting a few indistinct lines
of growth, smooth.

Casts of the interior have strongly projecting beaks. The internal characters of
the shell, so far as they can be made out from these casts, are as follows: Hinge
line very slightly arcuate, with eight to ten strong teeth behind the beaks and fifteen
or sixteen smaller ones in front of them. Anterior and posterior muscular impres-
sions subequal, distinct, the posterior one drawn out along the hinge margin, Above
the anterior pair there is another much smaller elongated pair lying close to the
hinge.

LAMELLIBRANCHIATA. 593

Otenodonta medialis.)

This species is distinguished from C. /evata Hall, sp., by its shorter form, abruptly
truncated posterior end and subalate antero-cardinal region, and in the posterior
instead of anterior position of the beaks. In casts of the interior the beaks are also
smaller and more prominent. C. abrupta Billings, is more ventricose, longer and not
so high anteriorly. The two species next described are more closely related.

Formation and locality—Good specimens of this species are exceedingly rare, but illy preserved
casts of the interior, which are provisionally referred here, are not uncommonly associated with C. socialis
in the middle third of the Trenton shales at Minneapolis and other localities in the state of Minnesota.

CrENODONTA MEDIALIS, ”. Sp.

PLATE XLII, FIGS. 50—52.

This species seems to occupy an intermediate position between C. nitida and
C. scofieldi. From the first it differs in having the beaks situated about midway
between the extremities, the posterior end longer, more oblique and more narrowly
rounded at the extremity, and the anterior end shorter and blunter in the antero-
cardinal region. The posterior part of the back is wider, because the umbonal ridge
is somewhat stronger and extends farther downward. Finally, the hinge plate is
more curved and appears relatively wider. From C, scofieldi it differs in having the
beaks centrally situated instead of one-third of the length from the anterior extrem-
ity, the umbonal ridge less sharp, the posterior end shorter and wider, and the hinge
plate stronger and more numerously denticulate. A careful estimation of the value
of the differentations leads me to believe that the form under consideration is more
closely related to C. nitida than to C. scofieldi. Perhaps it would be sufficiently dis-
tinguished as a variety of the former.

Another form of this type is represented by two casts of the interior in the Sur-
vey collection (Mus. Reg. No. 8311) from the “Lower Blue” limestone at Janesville.
Wisconsin. In these specimens there is an antero-cardinal wing as in C. nitida, but
the posterior end is too long for that species, the beaks being slightly in front of the
midlength instead of behind. C. leveta Hall, sp., also seems to belong here, but it is
not safe to say anything positive about that species till the original New York types
have been subjected to a critical examination.

Formation and locality.—Middie third of the Trenton shales, Minneapolis and near Cannon Falls,
Minnesota. A cast of the interior from the Galena shales of Goodhue county, probably belongs here.

CTENODONTA SCOFIELDI, 7”. Sp.
PLATE XLII, FIGS. 53—5s.
Shell small, strongly convex, transversely somewhat acuminate ovate, broadly

rounded in front and below, narrow behind, with small, prominent, incurved beaks,
—38

594 THE PALEONTOLOGY OF MINNESOTA.

(Ctenodonta socialis.

directed posteriorly and situated about one-third of the length from the anterior
extremity; umbones carinate behind, the ridge having a distinctly concave outline
in a side view; posterior end of hinge projecting slightly beyond the ridge, so that
the post-dorsal region is not quite flat. Hinge plate comparatively short and weak,
widest posteriorly, very narrow beneath the beak and in front of same; denticles
small, seventeen or eighteen in each valve, in a continuous series, about eight of
them posterior and larger than the others.

This neat and constant form is readily distinguished from C. nitida and C. medi-
alis, its nearest congeners, by the posteriorly carinate umbones, the less central
position of the beaks, its narrower posterior extremity and much weaker hinge plate.
The denticles also are less numerous. Casts of the interior of these three forms are
difficult to distinguish, but the task is not by any means hopeless when the speci-
mens are in a good state of preservation. The species is named for my colaborer on
the Gastropoda, Mr. W. H. Scofield, of Cannon Falls, Minnesota.

Formation and locality.—An entire example and nine valves were collected in the middle third
of the Trenton shales in the vicinity of Cannon Falls. Minnesota. A cast of the interior was
obtained at Minneapolis from the same beds. The species has not been observed in the upper third
of the shales, but the overlying Galena shales have furnished a number of casts that I have not suc-
ceeded in distinguishing. These were collected at Cannon Falls and near Kenyon.

CTENODONTA SOCIALIS, ”. Sp.

PLATE XLII, FIGS. 59 and 60.

Shell very small, moderately convex, transversely subovate, rarely exceeding
6 mm. in length, the average size about 3.8 mm. high by 5 mm. long; beaks small,
turning slightly toward the short posterior extremity behind which it is situated
between one-fourth and one-third of the entire length; umbonal ridge inconspicuous,
the convexity of the valves being relatively uniform. Surface almost smooth, no
markings save a few obscure concentric lines having been observed. Hinge plate
narrow, especially so under the beaks, widest posteriorly, comparatively long, arcuate,
the amount of curvature varying according to the length of the posterior end of the
shell, being greater when this part is shorter than usual; denticles small, nineteen
or twenty in each valve, six or seven of them posterior, several of the latter consid-
erably larger than any of the others.

In a shell of this kind it is very difficult, if not impossible, to decide beyond the
possibility of error which end is the anterior and which the posterior. In this case
I have assumed that the short side is the posterior, because this end of the hinge
plate is the wider and bears the largest denticles, that being the prevailing condition
among species of this section.

The small size, rather regularly oyate outline, moderate convexity and the

LAMELLIBRANCHIATA. 595

Ctenodonta fecunda.]

posterior position of the beaks are features that render the identification of this
species unusually easy. I hesitated to say whether it should be regarded as nearer
C. nitida or those ovate shells, like C. albertina, in which the larger side is undeniably
the posterior.

Formation and locality.—This small shell occurs in great numbers in certain layers of the middle
third of the Trenton shales at St. Paul, Minneapolis, Cannon Falls, Chatfield and other localities in the
state. The surface of a layer may be completely covered by separated valves or by casts of the interior.
The latter condition is the prevailing one at the two localities first mentioned, but in Goodhue and
Fillmore counties testiferous examples are the rule. In central Kentucky the species is occasionally
met with in the Modiolodon oviformis beds of the Trenton.

Mus. Reg. No. 8627.
Crenoponta FEcuNDA Hall.
PLATE XLII, FIGS. 67—73.
Nucula (Teltinomya) fecunda HALL, 1862. Geol. Sur. Wis., vol. 1, p. 55. (Figured, but not _described.)

Shell small, 9 mm. to 13 mm. in length, rather ventricose, transversely ovate or
obscurely subrhomboidal in outline, with the umbones rather prominent and full,
and the beaks incurved, directed slightly forward and situated about one-third of
the length behind the anterior extremity; base usually a little prominent in the
middle, somewhat straightened, or at any rate less convex in the posterior than in
the anterior half; posterior end narrower than the anterior, the outline sloping
forward rapidly above the produced lower part and merging almost gradually into
the post-cardinal margin; antero-cardinal outline more or less distinctly concave;
posterior umbonal ridge rounded. Surface marked by very fine, regular concentric
strie and strong wrinkles of growth, crossed by delicate radial lines, the network
thus formed requiring a magnifying lens to make it plainly visible. The radial
lines, however, are not often preserved.

The majority of the specimens seen are casts of the interior, mostly in an excel-
lent state of preservation. Asarule, they are marked by a limited number of obscure
concentric furrows. The muscular scars and pallial line are always faintly defined
Hinge plate rather narrow, arcuate, nearly two-thirds as long as the shell, with about
eighteen denticles in each valve; denticles very small under the beaks, where the
series seems also to have been interrupted by a small space; on each side of the
beaks they become larger gradually and at the same time assume an oblique direc-
tion, the upper ends of the teeth being turned away from the beaks.

Three specimens, illustrating slight variations, have the following dimensions:
Length, 10.5, 11.0 and 13.0 mm.; hight, 7.0, 8.0 and 10.0 mm.; thickness, 4.5, 6.5 and
6.8 mm.

This very common shell is certainly distinct from C. levata, C. nitida and C. sco-
fieldi, the anterior end being narrower and in two cases also shorter, while the

596 THE PALEONTOLOGY OF MINNESOTA.

(Otenodonta calvini.

hinge, with its oblique teeth, is very different. In C. socialis the outline is more
regularly oval and the beaks situated as much behind the center as they are in front
of that point in C. fecunda. In C. simulatrix the anterior end is wider, the muscular
scars deeper and the hinge more numerously denticulated. Similar differences dis-
tinguish C. albertina, a well marked species having also a stronger hinge and genicu-
lated teeth. The following species, C. calvini, is probably nearer than any other
species now known.

Formation and locality.—Very abundant in the lower so-called Maquoketa shales near Dubuque,
Iowa; Scale’s Mound, [linois, and Platte’s Mound in Lafayette county, Wisconsin. The species occurs
also in Fillmore county, Minnesota, in equivalent beds (Hudson River group), though but rarely.

CTENODONTA CALVINI, %. Sp.

PLATE XLII, FIGS. 61—64.

Shell subquadrate-ovate, about 15 mm. long, 12 mm. high and 6 mm. thick;
anterior end rounded, a trifle narrower than the slightly truncate posterior end;
the latter is a little oblique, gently convex except below, where the outline turns
rather sharply into the broadly rounded base; above it forms an obtusely angular or
rounded junction with the straight post-cardinal margin; in front of the scarcely
_ prominent beaks, which are situated about one-third of the entire length behind the
anterior extremity, the outline is more or less concave. Surface of valves rather
uniformly convex, with the posterior umbonal ridge strongly rounded, though in no
case conspicuous. External surface markings not observed. Casts of the interior
exhibit a few concentric undulations, and in the central and ventral parts a variable
uumber of obscure rays. The test seems to have been unusually thin. Hinge plate
very narrow, bent at the beak, straight behind, gently concave in front; denticles
small, oblique, about. sixteen posterior and eight or ten anterior in each valve.
Adductor muscular scars very slightly impressed, the posterior one extended above,
larger and longer than the anterior, and placed in the middle of the cardinal slope,
so that its long axis is parallel with the umbonal ridge; several small umbonal scars
may be observed.

This fine species, though closely related, is at once distinguished from C. fecunda
by its greater posterior hight and larger size. The convexity of the valves also is
somewhat less, and other differences may be detected in comparing the figures
of the two species on plate xtu. A nearer form, perhaps it ought to be called a
variety, occurs in the lower beds (Utica horizon) of the Cincinnati group at Coving-
ton, Kentucky. This has exceedingly fine and crowded concentric striw, crossed by
more distant radiating lines. Casts of the interior have about the same shape as
C. calvini, but they are all much smaller, the largest having a length of only 7 mm.

LAMELLIBRANCHIATA. 597

Otenodonta madisonensis.]

The concentric undulations also are more numerous. Ina paper soon to be published
I shall propose the name Ctenodonta mundula for this small form.

The three species mentioned in the preceding paragraph occupy an isolated
position in the genus, and, though they may resemble some of the species of the
levata section, I am satisfied that they are widely removed from them all. The
shape of the anterior end is peculiar, as is also the reticulate surface ornamentation
and the thin hinge plate with its oblique teeth.

The species under consideration is named for Prof. Samuel Calvin, State Geolo-
gist of Iowa.

Formation and localityx—Maquoketa shales (Hudson River group), at Graf and other localities in
northern Iowa. Also at Scale’s Mound in northwestern Illinois.

Mus, Reg. No. 8628.

CrENODONTA MADISONENSIS, ”. Sp.

PLATE XLII, FIGS. 65 and 66.

Shell subovate, slightly oblique, moderately convex, 12.5 to 15 mm. in length, 10
to 12 mm. in hight, and 5.6 to 7 mm. in thickness; anterior end very short, rounded,
posterior margin a little oblique, base broadly rounded and continuing into the
anterior margin; dorsal outline slightly concave. Beaks anterior, small, scarcely
prominent, incurved; posterior umbonal ridge rounded, inconspicuous; greatest con-
vexity of valves in front and above the center. Surface almost smooth, only two or
three obscure lines of growth having been noticed. Test rather thick, hinge strong,
posterior denticles geniculated.

This shell was included in this report and figured under the erroneous impres-
sion that it represented a variety of C. calvini. Since the plates were prepared,
however, another examination showed differences not before noticed, and when
finally the shell was removed from one of the specimens so that a part of the hinge
was uncovered, it became fully evident that it was not only distinct but belonged to
quite another group of species. It is namely not far removed from such species as
C. albertina and C, filistriata of this report, while it is especially near an unpublished
form from the middle beds of the Cincinnati group in Kentucky and Ohio which I
shall call C. tumida. From these three species C. madisonensis is distinguished by
the more uniform curvature of the anterior margin, the antero-cardinal region in
those forms being more or less prominent and subangular in outline.

Formation and locality..—The specimens upon which the species is founded were collected in the
Cincinnati group at Madison, Indiana, where they occurred in association with Ovthis retrosa,

598 THE PALEONTOLOGY OF MINNESOTA.

[Ctenodonta albertina.

CTENODONTA ALBERTINA, 7%. Sp.

PLATE XLII, FIGS. 76—80.

Shell subovate, widest in the anterior half, 10 to 18 mm. in length; beaks mod-
erate in size and prominence, situated about 4.5 mm. behind the anterior extremity
in a specimen 16 mm. long; antero-cardinal region compressed, slightly alated,
subangular in outline; anterior margin nearly vertical and rather gently convex
above the lower part, where it turns somewhat rapidly backward into the broadly
rounded base; the curvature of the basal outline is often not quite uniform, being,
in these cases, a little stronger in the anterior than in the posterior half; posterior
margin somewhat obliquely rounded-subtruncate; as shown in the figures the width
of the posterior end is somewhat variable; cardinal margin nearly straight; umbonal
ridge rounded, inconspicuous. Surface almost entirely smooth.

In casts of the interior the beaks are prominent, compressed and very little
incurved, the adductor muscular scars are distinct, the posterior one being especially
prominent and the larger, while the anterior one is drawn out above almost to the
point of the beak; the posterior cardinal outline is strongly concave, while the dor-
sum in this part is formed by a sharp curved ridge running backward from each
beak to the adductor scars and enclosing the area that had been occupied by the
hinge plates. The hinge plate is strong, contracted and bent beneath the beak, the
posterior part one-third longer than the slightly declining anterior part; denticles
strongly geniculated and deeply interlocking, the continuity of the series distinctly
interrupted under the beaks by an illy defined pit-like space. In five valves the
total number of denticles ranged from twenty-nine to thirty-two, with thirteen,
fourteen or fifteen anterior and sixteen or seventeen posterior. In a sixth valve,
unusually short and possibly not belonging to this species, there are only eleven
anterior and thirteen posterior teeth.

Length of an average example, 12 mm.; hight, 9.5 mm.; thickness,6mm. Ina
large specimen these dimensions are respectively 16, 12.2 and 7 mm.

The type of structure exhibited in this species and in C. filistriata, C. madisonensis
and two as yet unpublished forms from the Cincinnati group of Ohio and Kentucky,
stands somewhat apart from the other two types (7. e. C. nitida and C. fecunda)
included in this section of the genus. The geniculated hinge teeth and the pit
beneath the beak are peculiar features, while another difference, when compared
with the C. nitida type, appears in the absence of the small accessory scars over the
adductors. That some importance attaches to the absence of these small scars is
indicated by their constant presence in the species which pertain strictly to the
nitida type in other respects. These scars seem to be wanting in the shell of the

LAMELLIBRANCHIATA. 599

Ctenodonta filistriata ]

C. fecunda type as well, but this, unless we agree that the short side in those shells
is really the posterior, does not bring them much nearer to the C. albertina type,
since the adductors are reversed, the acuminate-ovate scar being anterior in the
latter and posterior in the former.

Formation and locality—A common species in the upper beds of the Cincinnati group at Clarksville
and other Jocalities in Ohio. I am not entirely satisfied that the species occurs in Minnesota, but there
are good reasons to believe that it may be found in the Hudson River strata near Spring Valley.

CTENODONTA FILISTRIATA, ”. Sp.

Fig. 44. a, right side of a cast of the interior of Ctenodonta filistriata, n. sp.: b and ¢, cardinal
and lateral views of left valve of same; d, small portion of surface of same, highly magnified; e, hinge
of a right valve of same, x 2; specimens from lower beds of the Cincinnati group at Covington, Kentucky:
f and g, cardinal and lateral views of a large right valve of Ctenodonta gibberula Salter, from the lower
Trenton near Murfreesboro, Tennessee.

over

Tellinomya levata HALL and WHITFIELD, 1875. Pal. Ohio, vol. ii, p. 82. (Not Nucula levata Hay,
1847, Pal. N. Y., vol. 1, p. 150.)

This species may be distinguished at once from C. albertina, with which it agrees
more closely than any other known, by the delicate, crowded, thread-like concentric
lines which cover the entire surface. Twelve to twenty of these lines may be counted
in a space 1 mm. wide. The shape and general appearance of the shell is very simi-
lar in the two shells, but the basal margin in the present form is always uniformly
rounded, while the antero-dorsal angle is a trifle blunter. The latter fact is due to
the greater bend in the hinge. The pit beneath the beak is scarcely so distinct as
in that species, and as the hinge is a little shorter the number of denticles is less
than the average number for C. albertina, there being usually twelve anterior and
fifteen posterior. Finally, in perfect casts of the interior the beaks are not so much
compressed and the ridges running posteriorly from them less sharp.

This species is generally identified with Hall’s Nucula or Tellinomya levata, origin-
ally described from the Trenton limestone of New York, and closely related to C.
nitida of this report. The error of this identification is so palpable that it is really
not worth the while to refute it. Any one at all capable of distinguishing species
must, now that attention has been directed to the matter, see at once that the two
shells are very different.

Formation and locality.—In the lower beds of the Cincinnati group at numerous localities in and
near the city of Cincinnati. A single specimen was collected by Mr. Charles Schuchert in equivalent
beds at Granger, Minnesota.

Mus, Reg. No. 8378.

600 THE PALEONTOLOGY OF MINNESOTA.

(Ctenodonta simulatrix.

CTENODONTA SIMULATRIX, #. Sp.
PLATE XLII, FIGS. 74 and 75.

In its general aspect this species greatly resembles C. albertina, and yet it is a
widely distinct form, the hinge being quite different in the two forms. The hinge
plate in C. stmulatriz is much narrower and more uniformly arcuate, the denticles
are more numerous and the majority straight and very small. Posterior to the
beak, beneath which the continuity of the series is slightly interrupted, there are
about twenty-five denticles; in front of the beak the specimen preserves only six
teeth, but, judging from other species, their number on this part of the hinge cannot
have been less than twelve and probably was quite as many as fifteen, making a
total for the entire hinge of from thirty-seven to forty. Comparing outlines, it will
be found that in the present species the ends are more regularly curved and the
beaks situated a little farther from the anterior extremity.

Formation and locality.—Upper part of the Hudson River group near Spring Valley, Minnesota.

C. recurva section (Palwoconcha, Miller.)

CrenopontTa comPpREsSsA Ulvyich.
PLATE XXXVII, FIG. 29; PLATE XLII, FIGS. 88—90.

Tellinomya compressa ULRICH, 1892. Nineteenth Ann. Rep. Geol. and Nat. Hist. Sur. Minn., p. 216.

Shell rather small, somewhat oblique, compressed convex, the length and hight
respectively as twelve or thirteen is to fourteen; convexity about half the length;
upper half triangular, the lower somewhat obliquely semielliptical; beaks small,
compressed, acuminate, curving backward; umbones rather flat, the convex part of
the valves terminating somewhat abruptly along the anterior and posterior cardinal
margins. In the outline these two margins, meeting at the beaks, form an angle of
about 85°, with the anterior gently convex and the posterior correspondingly con-
cave, or a little straighter. Antero-dorsal edge flattened but unusually narrow, with
- an obscure furrow on each side of the raised contact line; posterior lunette obscurely
defined. Surface with very fine, regular, raised, concentric lines, six to eight in 1 mm.

Hinge plate bent rectangularly, very wide in the central part; denticles mostly
transverse to the hinge, arranged in two distinct series, increasing gradually in size
and curvature away from the beaks, about twenty-two anterior and twelve posterior.
A wide crescent-shaped flat space, over which the teeth do not extend, forms the
inner border of the hinge plate. Just in front of the point of the beak, and sepa-
rating the two series of denticles, is the narrow end of an obscurely defined, curved
depression, extending more than two-thirds the distance across the hinge plate.

LAMELLIBRANCHIATA. 601

OCtenodonta intermedia.]

Adductor sears subovate, situated immdeiately beneath the ends of the hinge, dis-
tinct, the posterior one the deeper and margined on the inner side by an obtuse
ridge-like swelling. Small accessory scars have not been observed.

A single imperfect valve was all I had seen of this species when I first deseribed
it. During the summer of 1892, however, I succeeded in collecting an excellent
series of specimens, so that Iam now enabled to present the shell in all its characters
and to point out those which are really distinctive. Compared with C. astartiformis
Salter, of which an authentic example is now before me, it differs externally in its
greater proportional width, somewhat narrow posterior curve, less convex valves,
finer concentric lines and in wanting the coarse wrinkles of growth which seem to
be a constant feature of the ventral half in that species. Internally the muscular
scars and the denticles of the hinge are about the same in the two species, but the
hinge plate is considerably wider in the Minnesota form, while the flat space beneath
the denticles of the latter is scarcely represented in Salter’s species. Casts of the
interior of the two species are not easily distinguished, the only reliable differences
between them, so far as observed, being the lesser prominence and more uniform
curvature of the anterior margin and the slightly greater convexity of the casts of
C. astartiformis.

Formation and locality.—Upper part of the middle third of the Trenton shales at several localities
in Goodhue county, Minnesota. Casts belonging to this species or to C. astartiformis, the latter probably,
have been found in the upper part of the Trenton limestone at Minneapolis and at Janesville, Wisconsin,
and I have specimens of a very similar, though smaller, form from the upper third of the Trenton shales.

CTENODONTA INTERMEDIA Ulrich.
PLATE XLII, FIGS. 95-97.
Tellinomya intermedia ULnicn, 1892. Nineteenth Ann. Rep. Geol. and Nat. Hist. Sur. Minn., p. 218.

Shell thin, of medium size, moderately ventricose, rather erect, the hight a little
greater than the length. Outline subtriangular, at the beaks, which are obtusely
acuminate and incurved, forming very nearly a right angle; anterior cardinal margin
very gently convex, posterior cardinal edge correspondingly concave, ventral margin
together with the curve into the ends forming a semicircle. Ends subequal, the
posterior sometimes a little the longest. Umbones full, the remainder of the surface
sloping uniformly to the free margins. An obscure sulcus may be detected near the
anterior margin, and along the dorsal part of this end the surface descends abruptly
to the hinge plate. Surface with strong, closely arranged, thread-like, concentric
lines, about twelve in 5 mm. At intervals of about 2 or 5 mm. generally a fold
stronger than the rest.

Casts of the interior exhibit a faint ridge and sulcus in the anterior end, and

602 THE PALEONTOLOGY OF MINNESOTA.

[Ctenodonta alta,

two sharply defined muscular scars and pallial line in each valve.* Hinge plate
rather narrow, the teeth numerous, over thirty, as usual very small centrally, grow-
ing larger gradually towards the ends of the hinge.

This species is distinguished from C. astartiformis Salter, by its larger size, greater
width, more erect form, and comparatively coarse and regular concentric lines. C.
compressa is not so convex, especially in the umbonal region, has more pointed beaks
and much finer striz.

Formation and locality—Not uncommon in the middle division of the Galena at Wykoff and other
localities in Fillmore county, Minnesota.

Crenoponta ALTA Hall.

ra

PLATE XLII, FIGS. 93 and. 94.

Tellinomya alta HALL, 1861. Rep. Supt. Geol. Sur. Wis., p. 27; MEEK and WortTuEN, 1868, Geol.
Sur. Il1., vol. iii, p. 309.

Shell (internal cast) small, rather strongly convex, nearly erect, subtriangular,
the length, hight and convexity, respectively, about 11.2, 11.5 and 6.8 mm.; base
broadly rounded, semielliptical; beaks elevated, nearly central, arching slightly back-
ward; anterior and posterior sides nearly equal, sloping abruptly from the beaks at
an angle of about 85°, the anterior dorsal outlines very gently convex, the posterior
correspondingly concave; beneath the ends of the hinge the outline on both sides
curves rapidly into the base. Muscular scars large and comparatively distinct, the
posterior one nearly rounded, the other more oval; the anterior one lies in the wider
lower end of a shallow sulcus which may be traced almost to the beaks. The hinge,
Prof. Hall says, is marked by from twenty to twenty-five very small curved teeth on
the anterior (posterior) side and from ten to fifteen on the posterior (anterior) side.

This rare species is a little smaller, not quite as high, more erect and less convex
in the basal outline than C. intermedia. In the latter, as well as in all the other -
species of this section of the genus, save C. recurva, the anterior half of the outline

is more uniformly rounded.

Formation and locality.—The specimen described by Meek and Worthen came from the Galena
near Mount Carroll, Illinois, while Hall’s original type is from, presumably, an equivalent horizon at
Dodgeville, Wisconsin. The specimen here used, which is precisely like the Illinois example, is from
the shaly lower beds of the Galena near Fountain, Minnesota.

*In the original description it is stated that a small pair of scars is situated above the posterior adductor unre S-
sions. This statement I now believe rests upon faulty observation.

LAMELLIBRA NCHIATA. 605

Ctenodonta recurva.]
Crenoponra RECURVA Ulrich.
PLATE XLII, FIGS. 98—101.
Tellinomya recurva Uuricn, 1892. Nineteenth Ann. Rep. Geol. and Nat. Hist. Sur. Minn., p. 221.

Shell small or of medium size, compressed-convex, slightly oblique, subtriangu-
lar, the length and hight almost equal, the thickness equalling about one-third of
the hight. Rostral portion strongly recurved, ends narrowly rounded, base nearly
semi-elliptical, with more curvature in the posterior half than in the anterior.
Beaks prominent, posterior to the center of the shell; umbones with an unusually
small degree of convexity. Cardinal margins sharply inflected, forming an elongate
depressed area on the anterior side and a shorter, narrowly cordiform one behind or
rather beneath the beaks. A shallow and gradually widening sulcus extends from
the beak along the antero-cardinal margin to the antero-ventral border. Surface
marked by several strong lines of growth and between them fine concentric strie,
about ten in 3mm. Hinge plate strong, bent at a right angle, the posterior part
nearly straight (gently concave), somewhat shorter than the anterior, with about
twenty small, curved transverse teeth, decreasing, as usual, gradually in size and
curvature toward the beak; anterior part convex, with about thirty teeth. Consid-
ering the strength of the hinge plate, the teeth are very small. Immediately in
front of the beak, in the angle of the hinge, a narrow oblique space breaks the
continuity of the series of denticles. Hinge plate margined on the outer side by a
delicate sharp ridge; just within it a narrow furrow which has considerable width
and depth for some distance in front of the beak. In front of the beak and above
the marginal line of the hinge plate a small area is defined apparently for the recep-
tion of an external ligament. (See note, p. 578.) Anterior and posterior muscular
scars distinct, though not very strongly impressed; as usual for this section of the
genus in size and form.

The compressed form reminds of C. compressa, but the shape is different, the
length being greater, the ends more narrowly rounded and the rostral part more
strongly recurved. The surface markings also are coarser and the posterior lunettes
much better defined, while a number of important differences may be observed in
their hinges. Hall’s C. alta is similar in the basal part, but is a more convex shell
and much less curved in the rostral part.

Formation and locality.—Upper beds of the Hudson River group, at several localities in Fillmore
county, Minnesota. It is associated with the next species (C. similis), but is not nearly so abundant.
The species occurs, though so far as observed only in the condition of casts, also at Oxford, Waynesville
and other localities in Ohio, and at Richmond, Indiana.

604 THE PALEONTOLOGY OF MINNESOTA.

[Ctenodonta similis.

Crenoponta simiiis Ulrich.
PLATE XLII, FIGS. 102—106.

Tellinomya similis ULRICH, March Bs) 1892. Nineteenth Ann. Rep. Geol. and Nat. IES Sur. Minn.,

Tellinomya (Nucula) lepida yenees April 9, 1892. Bull. Minn. Acad. Nat. Sci., vol. iii, p. 339.

Shell small to medium size, moderately ventricose, subtriangular, the length
and hight respectively as five or five and a half is to six. Umbones full, rounded,
the rostral portion rather strongly recurved, with the beaks small and projecting
slightly above the hinge. Antero-dorsal edge convex, thick, flattened, but not
sharply defined. Postero-dorsal edge rather strongly concave, impressed so as to
form an illy-defined imperfect lunette. Anterior outline almost uniformly convex,
curving neatly into the well rounded ventral margin; posterior side rather narrowly
rounded. Surface of valves almost uniformly convex, highest a little above the
center, generally with a few well marked varices of growth and with finer concentric
lines in the lower part. Hinge plate of moderate strength, with numerous small
teeth (thity-five to forty-two); in the largest examples seen with about twenty-seven
anterior and fifteen posterior to the beak; posterior teeth the largest. Muscular
scars moderately impressed, always distinguishable.

The shape of this shell is exceedingly like that of C. astartiformis Salter, though
as a rule proportionally a little longer and scarcely so ventricose. The posterior
lunette also is somewhat deeper, but the principal differences le in the hinge. The
hinge plate, namely, in Salter’s species, is somewhat stronger, while the denticles
are more bent, larger and less numerous. The teeth, furthermore, are largest on the
anterior side, while in C. similis the opposite is the case. It is also very much like
the associated C. recurva, but is distinguished by being a little higher, more uniformly
rounded on the anterior side and without the anterior sulcus. More important dif-
ferences are the greater tumidity of the umbones, less prominent beaks, less strongly
defined anterior and posterior lunettes and weaker hinge plate. Casts of the interior
are separated chiefly by the greater thickness of the rostral portion. They are also

nearly always of smaller size than those of C. recurva.

Formation and locality.—Upper beds of the Hudson River group, Spring Valley and other parts
in Fillmore county, Minnesota, and at Blanchester, Ohio.

CrmnoponTa oBLigua Hall.
PLATE XLII. FIGS. 8&3—87,

Nucula obliqua HALL, 1845. Amer. Jour. Sci. and Arts, vol. xliii, p. 292.
Tellinomya ? obliqua Mek, 1873. Pal. Ohio, vol. i, p. 139.
Paleoconcha obliqua and P. faberi MILLER, 1889. North Amer. Geol. and Pal., p. 498.

Shell very small, broadly acuminate-subovate; or, without the triangular rostrum,

LAMELLIBRANCHIATA. 605

Ctenodonta hamburgensis.]

the outline may be called subcircular, the basal half, as a rule, being quite regularly
curved; length and hight nearly equal, the latter dimension commonly a little the
greater. Beaks prominent, situated behind the center, turned backwards. Surface
marked by comparatively strong concentric lines.

On casts of the interior, and this is almost invariably the condition in which the
species is preserved, the muscular scars are nearly always distinguishable and the
posterior one is often sharply defined and prominent on the upper side. They are
situated just within the ends of the shell and each near the wider and lower end of
an obscurely defined sulcus. The two sulci, of which the anterior one is usually the
better marked, begin near the beak and extend down on each side to the base of the
muscular scars. A small accessory scar has been observed immediately above the
posterior adductor. Pallial line simple, rather distinct. Hinge plate comparatively
strong, with numerous (at least thirty) small denticulations.

The size of this shell varies greatly. Many of the specimens found at Cincinnati
and localities in the vicinity of that city are less than 2 mm. in diameter, but others
are occasionally met with that range from that size to a diameter of 5mm. In the
northwestern localities the species grew to a larger size, specimens having a diameter

- of from 5 to 7 mm. being in the majority. Aside from the matter of size, however,
the specimens from these two regions are practically identical.

Dr. S. A. Miller, in the work above referred to, erects a new genus, Palwoconcha,
and a new family for the reception of the present species, which he divides into two
species, giving to the larger form the specific name faberi. But this new genus and
family have no right to recognition, since they are based entirely upon erroneous
observation, he having come to the conclusion that the hinge in these shells was
not denticulated and probably edentulous. Through the kindness of Dr. Miller I
had an opportunity to examine a number of the specimens (excellent casts of the
interior) used by him in defining his genus. Even among these I noticed several
that retained undeniable evidence of the denticulate hinge.

Formation and locality.—Very abundant at Cincinnati, Ohio, and numerous other localities in the
the vicinity of that city. In the northwest it is one of the rare fossils of the so-called ‘*Nucula bed”
of the Maquoketa or Hudson River shales.

CreNODONTA HAMBURGENSIS Wa/colt.
PLATE XLII, PIGS. 91 and 92.

Tellinomya? Hamburgensis WALcorTT, 1884. Pal. Eureka District, p. 76.

Shell small, rather convex, rounded-subrhomboidal in outline, with the hight
and length subequal and the beak comparatively large, incurved and situated in
front of the center; posterior dorsal margin somewhat straightened. Surface

606 THE PALEONTOLOGY OF MINNESOTA.

[Clidophorus,

marked by regular sharp, though fine, concentric strie in the posterior half, the
anterior half appearing smooth. Hinge and interior unknown.

The single specimen of this form seen from Minnesota, agrees so well in its
outline and general appearance with Walcott’s figures of 7. hamburgensis that I am
obliged to refer it to his specieis. It should be remarked, however, that the surface
of the Nevada types of the species is described as presenting ‘a smooth, glistening
appearance,” giving them “the character of some of the Linguloid shells,” and that
it is marked by not only concentric lines but also by “very fine, often scarcely per-
ceptible radiating strie,’—all of which is wanting on the Minnesota specimen under
consideration. But, as these differences may all be due to different methods of
preservation, I have not taken them into account.

Respecting the generic position of the shell there may be some doubt, because
we have as yet no knowledge of the interior. Nor does the species seem to fit very
well into any of the sections into which the genus has been divided. Certain it is
that it is not very closely related to any of the numerous species described. Perhaps
it is the most like C. socialis, with which it is also associated, but it will be distin-
guished readily enough by its shorter and rounder form, fuller umbones and more
distinctly striated surface.

Formation and locality.—Upper part of the middle third of the Trenton shales, Chatfield, Minnesota.
The types of this species are from the upper part of the Pogonip group, Eureka District, Nevada.

Genus CLIDOPHORUS, Hall.

Clidophorus, HALL, 1847. Pal. N. Y., vol. i, p. 300.
Compare Nueulites, CONRAD, 1841. Ann. Rep. Geol. N. Y.. p. 49; and Cucullella, McCoy, 1855.

I prefer not to characterize this genus at the present time, nor to express any
definite opinion respecting its relations to Cucullella, McCoy, and Nuculites, Conrad,
for the simple reason that I have had no opportunity to study the typical species of
the genera. It should be stated, however, that many authorities regard the three
names aS synonymous and that, unless new distinctive features are brought out,
their views cannot be successfully combated.

CLipoPHoRuS consugTuS Ulrich.
PLATE XXXVII, FIGS. 32 and 33.
Clidophorus consuetus ULRICH, 1892. Nineteenth Ann. Rep. Geol.and Nat. Hist. Sur. Minn., p. 223.
Shell above the medium size for the genus, transverse, moderately elongate-

ovate, rather strongly convex, the length equaling nearly twice the hight. Beaks
small, incurved, flattened. Dorsal line convex, sloping downward behind the beaks

LAMELLIBRANCHIATA. 607

Clidophorus neglectus,]

to the narrowly rounded posterior extremity. Anterior end neatly rounded, wider
than the posterior. Ventral margin gently convex in the middle, more strongly and
almost equally curved at the ends. An obscure umbonal ridge traceable from the
beaks three-fourths of the distance to the posterior basal edge. Above it an
impressed narrow line, beyond which the surface descends rapidly to the dorsal
margin. Casts of the interior with a narrow, slightly curved, clavicular impression
just in front of the beaks, extending but little more than one-third of the distance
to the antero-basal margin. Surface of casts with a few obscure growth lines or
folds. Point of greatest convexity a little above and behind the center of the shell.
In a dorsal view the central half of the outline is very slightly flattened.

Length, 17.2 mm.; hight, 9.0 mm.; thickness of both valves, 5.8 mm.

This shell appears to be related to C. cwneatus and C, elongatus, described by Hall
from the Silurian rocks of Nova Scotia (Can. Nat. and Geol., vol. 5, pp. 148 and 150,
1860). It is, however, specifically distinct, the shape being different and the poste-
rior sinus situated higher up and very much less defined. C. planulatus (Conrad) and
C. ellipticus Ulrich, also have somewhat different outlines and have the cardinal
slopes less abrupt, the whole surface in those species being more uniformly and less
convex.

Formation and locality.—Middle Galena near Wykoff, Minnesota, where it is associated with Cteno-
donta intermedia.

CiipopHorus NEGLEcTUS [Lall.
PLATE XLII, FIGS. 20—25.

Clidophorus neglectus HALL, 1862. Geol. Sur. Wis., vol. 1, p.55. (Figured but not described.)

Compare Clidophorus (Nucula) fabula HAL, 1845. Amer. Jour. Sci. and Arts, vol. xliii, p. 295.

Shell varying greatly in size, the smallest observed having a hight of only 2.5
mm., with a length of 5 mm., while in the largest seen (from Graf, lowa,) these
dimensions are respectively 8.5 mm. and 16 mm.; thickness of the latter about
6 mm.

Shell transversly subelliptic, rather strongly convex; ends subequally rounded,
the anterior generally a little narrower than the posterior; the outline of the latter,
however, often exhibits a tendency to become angular just beneath the middle and
obliquely subtruncate above; basal and dorsal margin broadly convex. Beaks small,
somewhat tumid, placed about one-third of the length of the shell behind the ante-
rior extremity. Surface marked by fine concentric lines and several stronger varices
of growth; the latter show through the shell so as to be visible on casts of the inte-
rior. Hinge plate narrow, not over half the length of the shell, minutely toothed;
denticles twenty or more in each valve, three-fourths of the number being posterior

608 THE PALEONTOLOGY OF MINNESOTA.

[Lyrodesmida.

to the beaks, placed obliquely and so that they converge inwardly, the direction of
the anterior series being nearly at right angles to that of the posterior series.
Clavicle strong, nearly straight, almost vertical, sharply defining the somewhat semi-
circular and large anterior muscular scar and leaving a strong furrow in casts of the
interior just in advance of each beak. The furrow extends beyond the middle of
the distance to the basal margin. Posterior scar faint, smaller than the anterior,
_ occupying a central position on the post-cardinal slope. Several small umbonal
scars may be observed on good casts, and obscure rays are occasionally visible on
their sides.

Hall’s C. fabula, described from Cincinnati specimens less than 2 mm. in length,
seem to me to be nothing more than a dwarfed variety of this species.

Formation and locality.—In the so-called ‘‘Nucula Beds” of the Maquoketa (Hudson River) shales at
several localities in Lafayette county, Wisconsin; Jo Daviess county, Illinois, and near Dubuque and Graff
in lowa. It is to be found, I think, in the equivalent beds in Fillmore county, Minnesota.

Mus. Reg. No. 7336.
Family LYRODESMID, Ulrich.

A reconsideration of the génera included in this family, on page 486 of this work,
has convinced me fully that they are improperly associated and that the family must
for the present rest solely on the typical genus. Dr. 8S. A. Miller was, I now believe,
right in proposing a new family for his genus Technophorus (N. A. Geol. and Pal., p. 458,
1889), but he should have included the closely related Ischyrina, Billings, a genus
doubtfully referred by him to the Trigoniidw. The new genus Allodesma proves to
be related to Cyclochoncha, Miller, rather than to Lyrodesma and should therefore be
removed to the provisional family Cycloconchide.

The proper arrangement of these three families in a scheme of classification is
a point upon which it is very difficult to come to a satisfactory determination. Con-
siderable agreement in structure is to be traced between them, and at times I might
go so far as to say that they should be regarded as closely related. Still, in view of
the fact that each in one way or another resembles types classed in such widely
distinguished families as the Trigoniide, Crassutellide, Cyrenidw and Myide more
closely than they do known Devonian and Carboniferous forms, it would obviously
be an expression of opinion quite insufficiently supported by facts.

Genus LYRODESMA, Conrad,

Lyrodesma, CONRAD, 1841. Ann. Geol. Rep. N. Y., p. 51; HAwn, 1847, Pal. N. Y., vol. 1, p. 302.
Actinodonta, PHILLIPS, 1848. Mem. Geol. Sur. Great Britain, ii.

Shell moderately convex, larger than high, ovate to subquadrate, rounded in
front, usually obliquely truncate behind and more or less angular post-basally.

LAMELLIBRANCHIATA. 609

Lyrodesma acuminatum.]

Beaks small, placed in front of the midlength; posterior umbonal ridge generally
prominent, often angular; post-cardinal slope frequently with radiating lines, the
rest of the surface with concentric strie only. Hinge consisting of from six to eight
prominent, subequal, transversely striated teeth, radiating regularly from the beak
and placed on a thick plate, which leaves a large oblong depression in the dorsal
edge of casts of the interior. Adductor scars rather faintly impressed, the posterior
one larger than the anterior. Two pairs of small pedal muscles, the anterior pair
situated immediately above the anterior adductors, the posterior pair on each
side of the hinge line just behind the hinge teeth. Pallial line slightly sinuate
posteriorly.

Type: L. planum Conrad.

Of this excellently marked genus I know eleven or twelve American specific
forms. Eight of these occur in the various horizons of the Cincinnati group, the
remainder in the Trenton. Two additional species are catalogued by Bigsby among

the European Lower Silurian shells.

LyRODESMA ACUMINATUM, , Sp.

PLATE XLII. FIGS. 1—5.

Shell obliquely acuminate-ovate, the outline being drawn out to an acuminate
extremity posteriorly; in the typical form (fig. 1), the hinge line is arcuate and passes
gradually into the posterior margin, which, because of the flattening of this region
projects, in a side view, but little beyond the sharply angular umbonal ridge; anterior
end broad, regularly rounded; base straight posteriorly. Beaks small, arcuate,
strongly incurved, not very prominent, situated somewhat less than one-third of the
length from the anterior extremity. Surface with obscure, distant, concentric lines;
on the posterior cardinal slope four or five radiating lines. Hinge with six teeth of
which the anterior ones are considerably shorter than the posterior one, and the
central ones curved backward. Posterior adductor impression unusually distinct;
sinus in pallial line very small.

The specimen represented by figures 3 and 4 (plate XLII), is one of several that
I refer to this species with considerable doubt. The posterior end is too short caus-
ing the beaks to be more central, and the post-cardinal margin is more prominent
and subalated. The umbonal ridge is even sharper and more prominent, its greater
distinctness being due to a somewhat greater flattening of the flanks of the valves.
The hinge is injured in the specimen, but it is quite evident that the teeth have not
that backward sweep which marks the typical form. Precisely the same form (see

figure 45-h, page 611) occurs in the Trenton of Kentucky, but, so faras known, it is
—39

610 THE PALEONTOLOGY OF MINNESOTA.

{Lyrodesma cannonense.

not, as isthe casein Minnesota, there associated with the typical form. The variety,
which may take the name of intermedium, connects L. acuminatum with L. cincinnatiense
Hall, being as nearly as possible intermediate between these species. The form of
the shell and the prominence of the umbonal ridge will distinguish L. acuminatum
from all of the other species.

Formation and locality.—Middle third of the Trenton shaies, Chatfield and near Cannon Falls,
Minnesota. The var. intermedium occurs at the same localities and in the Trenton limestone near
Burgin, Kentucky.

LyYRODESMA CANNONENSE, ”. Sp.
PLATE XLII, FIGS. 6—8.

Nueula poststriata HAty, 1847. Pal. N. Y., vol. 1, p. 151, pl. 34, fig. 2a, 2b. (Not p. 301, pl. 82,
figs. 10a, b.)

This small species of which only casts of the interior have been seen, is similar
in shape to L. acuminatum var. intermedium. Critically compared it proves to be
longer, and has the beaks farther anterior. The hinge line also appears to have been
somewhat longer. Then there is a slight depression on the posterior side of the
umbones which is not seen on casts of that species. Tn all these respects L. cannon-
ense agrees very closely with L. subplanuwm, a new species from the Utica horizon of
the Cincinnati group, at Covington, Kentucky, which I am describing in vol. vii of
the reports of the Geological Survey of Ohio; and it is with that form that I believe
its relations really lie. Comparing it with an excellent cast of that shell, the
Minnesota form is distinguished by its shorter hinge line, more oblique posterior
margin, more sharply angular umbonal ridge, and wider beaks. Though also smaller
it cannot be denied that the two forms are very closely related, and probably nothing
more than varieties of one species. é

The Trenton shell referred to by Hall in 1847 (loc. cit.) to Nuculites (now Lyro-
desma) po.tstriatum Emmons, is not the same as the Hudson River type of that
species, but probably belongs to L. cannonense.

Formation and locality.—Galena shales near Cannon Falls, Minnesota. Also in the Trenton lime-
stone, Carlisle, Pennsylvania.

LAMELLIBRANCHIATA. 611

Lyrodesma major.)

LyropEsMA MAJOR Ulrich.

Cleidophorus major ULRICH, 1879. Jour. Cin. Soc. Nat. Hist., vol. ii, p. 25.

Fig. 45. a, right valve of Lyrodesma major Ulrich; 6, cardinal slope of same, x 2, showing the fine
radiating strive; c, interior of a right valve; d, hinge of same, x 2; e, left side of a cast of the interior of
same, Showing the muscular scars and pallial line with unusual distinctness; f, dorsal view of same, slightly
enlarged; g, vertical section through a valve at the beak, showing thickness of hinge plate and why the
beaks in casts are widely separated; specimens from upper beds of the Cincinnati group at Clarksville,
Ohio. h, right valve of Lyrodesma acuminatum, var. intermedium, from the Trenton near Burgin, Ken-
tucky. 7, dorsal view of a cast of the interior of Technophorus extenwatus Ulrich, « 2, showing the
united beaks, the flattening of the posterior dorsal edge and other features.

Shell transversely subovate, unusually elongate for the genus, narrow poste-
riorly; length of three testiferous examples 17, 24 and 25 mm., greatest hight of
same (from beaks to basal margin) respectively, 11, 15 and 18 mm.; greatest thiek-
ness subcentral, somewhat greater than half the hight; anterior margin rounded,
most prominent immediately above the middle of the hight, often straightened in
the upper half to the beaks; base broadly yet rather strongly convex; posterior end
long, somewhat attenuate, narrowly rounded at the extremity; cardinal outline
declining each way from the beaks, more or less concave behind them. Beaks rather
prominent, small, incurved, situated about one-fourth of the entire length from the
anterior extremity; umbones full, sharply rounded on the posterior side where the
surface descends abruptly to the cardinal margin; behind the beaks the dorsum is
first concave, then flat and finally low ridge-shaped; beneath, or rather in front of
them, there is an impressed line on each side which defines an elongated lanceolate
area. Surface nearly smooth, in one example exhibiting fine concentric stria. All
of the testiferous specimens however have twelve or more, fine radiating lines on
the posterior umbonal ridge and cardinal slope.

Hinge with six teeth in each valve, the four central ones much stronger than
the marginal pair. Muscular scars strongly impressed, the anterior adductor sharply
defined on the inner side by a thin ridge running down from the hinge, narrowing

above and surmounted by deep supplementary scars; posterior adductor elevated

612 THE PALEONTOLOGY OF MINNESOTA.

[Technophorus.

anteriorly, situated in the cavity of the umbonal ridge about midway between the
beaks and the posterior extremity of the shell; posterior pedal muscles strongly
defined, situated on each side of the cardinal edge and just behind the hinge plate.
Pallial line distinct, especially in front and along the base, sinuate posteriorly.

This fine shell is in no wise related to Clidophorus, to which genus I originally re- .
ferred the indifferently preserved casts upon which the species was founded. Had I
been acquainted with the appearance of casts of the interior of Lyrodesma, which are
really very distinctive, it is not likely that I should have been led astray by the slit-
like vertical depression in front of the beaks. Compared with other species of the
genus, L. major is unusually long posteriorly and narrow without running to an
acuminate extremity, the radiating lines on the umbonal ridge are finer and the
muscular scars deeper. The species is so distinct that detailed comparisons are
scarcely necessary. Still it may be well to say that L. acwminatum and L. cannonense
are pointed instead of rounded posteriorly and have much stronger umbonal ridges,
while they are also less convex in their basal outlines.

Formation and locality—A small valve apparently belonging to this species was found in the Hudson
River group near Spring Valley, Minnesota. Casts of the interior are not uncommon near the tops of the
hills about Cincinnati,Ohio. These are proportionally alittle longer than the geologically higher form of
the species which is represented in my cabinet’ by excellently preserved testiferous examples from the
upper beds of the Cincinnati group at Clarksville, Ohio.

Family TECHNOPHORIDA, Miller.
Genus TECHNOPHORUS, Miller.

Technophorus, MILLER, 1889. North Amer. Geol. and Pal., p. 514.

Shell small, equivalve, inequilateral, compressed convex, often attenuate and
extended posteriorly; anterior end rather short, wider than the posterior, almost reg-
ularly rounded in outline; beaks very small, scarcely, if at all prominent; one or two
sharp ridges, with a furrow above each, arise near the beak and extend in a curved
direction to the post-basal margin. Anterior part of surface marked with regular
concentric lines, generally separated by rows of minute puncte; on the posterior
part, especially the cardinal slope, those lines rarely coincide with the margins of
the valves, but assume various arbitrary and sometimes ornamental arrangements.
Internally a short and thick rib extends downward in each valve from the hinge
directly in front of the beaks, while on the posterior side of same a shorter oblique
rib, ora mere thickening of the hinge plate, causes the beaks in casts of the interior
to appear much more erect and prominent than they do on the exterior of the shell.
In casts the beaks of the two valves are not distinguishable but together form a single
pyramidal prominence. Anterior adductor scar small, situated immediately in front
of the internal rib; posterior scar and pallial line not observed, although most
excellent casts were studied.

LAMELLIBRANCHIATA. 613

Technophorus.]

Type: Technophorus faberi Miller.

The shells included in this genus are in several respects very remarkable. This
is true in the first place of their surface ornamentation in which they differ more or
less decidedly from all known paleozoic representatives of the class, with the possible
exception of Ischyrina Billings, a genus that will be discussed presently. As a sec-
ond, though no less important peculiarity, we have the character of the beaks as
these appear in casts of the interior. In all wholly known Lanellibranchiata, namely,
the beaks of the two valves are distinguishable in casts as two more or less promi-
nent points separated, as the case may be, by a narrow or wider depressed space
originally occupied by the hinge plate. In casts of Technophorus, on the contrary, the
fillings of the cavities of the two beaks forms a single pyramidal prominence. (See
fig. 45-i, p.611). Itisevident then that immediately beneath the beaks, the hinge plate
must be excavated, and a careful examination of the beaks of casts of 7’. extenuatus
brought to light certain faint markings indicating that the excavation was occupied
by either an internal cartilage or some peculiar type of muscle. The internal ribs
are also unusually short and thick, and peculiar in this, that they meet in the center
when the valves are closed so as to completely shut off the space occupied by the
anterior adductor muscles from the cavity under the beaks.

Unfortunately, the hinge proper is not shown by any of the specimens seen by
me. Still, one of the casts of 7. extenuatus shows a number of very small papilli
along both the anterior and posterior sides of the hinge line that may have been
produced by minute denticles on the hinge plate. But we cannot accept such uncer-
tain evidence, so that for the present the hinge must be regarded as incompletely
known. IJschyrina, Billings, so far as known to me from the description and figures
of the type species, J. winchelli (Desc. Catal. Sil. Foss. Island Anticosti, p. 16; 1866)
seems to be closely related to this genus. The internal ribs are better developed, the
posterior one especially. Billings represents the latter as quite distinct from the
hinge plate, which is not the case in Technophorus. There are posterior (Billings
calls this side anterior) furrows and ridges, but the wing is very short. The beaks
are stated to be small and obscure, but I have no means of knowing whether they
appear in casts as merged into a single prominence or not. J. plicata, described but
not illustrated by Billings on p. 52 of the same catalogue, seems to agree much better
with Technophorus faberi, and it is not improbable that it should be referred to this
genus instead of Ischyrina.*

* Since the above was written and placed in the bands of the printer, I have had an opportunity, which Lowe to the
kindness of the officers of the Geological Survey of Canuda, of studying the original types of Ischyrina winchelli and I, plicata,
In a cast of the interior of the first, the internal ribs are shown as represented by Billings. It shows further that the beaks
are pressed down to the hinge and, though the impression is of one valve only, the evidence Is fairly conclusive that the
beaks were united in casts as in Technophorus. The second species proves to be, as I suspected, a true Technophorus, with
close relations to 7, subacutus and T., punctostriatus. Its surface markings are minutely puncto-striate, with about eight of
the finely pustulose concentric lines in 1 mm,

614 THE PALEONTOLOGY OF MINNESOTA.

(Technophorus extenuatus.

TECHNOPHORUS EXTENUATUS Ulrich.
PLATE XXXVII, FIG. 34; PAGE 611, FIG. 45—i.
Technophorus? extenuatus ULRICH, 1892. Nineteenth Ann. Rep. Geol. and Nat. Hist. Sur. Minn., p. 222.

Casts of the interior small, compressed, somewhat elongate, alated and drawn
out posteriorly. Beaks small, erect, moderately prominent, together forming a low
pyramidal prominence, situated about one-fourth of the entire length from the ante-
rior extremity. Just in front of the beaks the casts of the interior exhibit a deep
though not very long impression; the posterior umbonal rib left an obscure furrow
on each side of the hinge line. Anterior end broad, rounded, most prominent in the
upper third; ventral margin broadly convex and slightly produced a little in front
of the middle; behind this point the outline is nearly straight (slightly concave)
sloping up toward the narrow (? pointed) posterior extremity. Cardinal line nearly
as long as the entire shell, gently concaye behind the beaks. A thin sharply defined
ridge, slightly curved, extends across each valve from the beak to the lower side
of the posterior end. Surface gently convex in the anterior half, faintly constricted
in front of the ridge, and marked with obscure, concentric wrinkles of growth. A
specimen preserving a small part of the shell, shows that the external surface is
marked, at any rate on the sides, by closely arranged, sharp, elevated lines, separated
by rows of small puncte.

Length about 21 mm., greatest hight 10 mm., greatest convexity about 3.5 mm.
This species, which I now regard as undoubtedly congeneric with the Cincinnati
shell upon which Dr. Miller founded the genus Technophorus, is distinguished by the
prominently rounded centro-basal margin, and the greatly produced posterior wing.

Formation and locality.—Middle third of the Trenton shales, Minneapolis and St. Paul, Minnesota.

TEcHNOPHORUS suBAcuTUS Ulrich.
PLATE XL, FIGS. 33 and 34.
Technophorus subacutus ULRICH, 1892. Amer. Geol., vol. x, p. 191.

Shell small, rather ventrizose, alated posteriorly, the hight and length respec-
tively as two is to three. Cardinal margin nearly straight, anterior end uniformly
rounded, ventral edge more gently curved, the posterier straight and sloping back-
ward slightly to the acuminate extremity of the hinge line. Ina cast of the interior
of a left valve, the small beak is erect, projects prominently above the hinge line,
and is situated about one-third of the entire length from the anterior extremity.
Just in front of the beak there is a strong and deep impression, running almost
vertically downward. On the anterior side this slit margins a rather large muscular
scar. Extending backward from the beak the cast exhibits another, but in this case,

LAMELLIBRANCHIATA. 615

Technophorus filistriatus.]

very obscure linear depression. The entire rostrum also is somewhat constricted,
presenting an appearance that may have been produced by a slight internal thick-
ening of the shell, extending from the anterior to the posterior umbonal rib. Two
curved folds, the posterior one the strongest, extend from the postero-ventral angle
toward the beaks, becoming indistinguishable, however, about midway between the
two points. Surface markings and hingement unknown.

Length 11.5 mm., hight 6.8 mm., convexity of one valve about 2.2 mm.

This incompletely known species is very similar in both the outline and general
expression to 7’, punctostriatus Ulrich, from the middle beds of the Cincinnati group in
Ohio and Kentucky. Though doubtless closely related, a careful comparison of internal
casts—the only condition in which the present species is known—proves that they can
be separated, the Minnesota species having the beaks more anterior and more prom-
inent, the anterior margin more uniformly rounded, and the post-cardinal outline
more concave, while the posterior ridges are more oblique and do not, as is the case
in casts of the Cincinnati shell, extend beyond the middle of the distance to the beaks.
None of the other species are near enough to require comparisons.

Formation and locality.—The specimen described was found in the upper part of the Trenton lime-
stone at Minneapolis, Minnesota. The same piece of stone contains numerous specimens of Orthis perveta
Conrad, and Zygospira (Hallina) nicolleti W. and S$.

TrcHNOPHORUS FILISTRIATUS Ulrich.

PLATE XL, FIGS. 35 and: 36.

Technophorus filistriatus ULRICH, 1892. Amer. Geol., vol. x, p. 101.

Shell small, though large for the genus, compressed, with the greatest convexity
in the anterior half, scarcely alate posteriorly, the hight and length as three is to five.
Beaks small, projecting very little, slightly incurved, one-third of the entire length
of shell from the anterior extremity. Anterior end much the widest, broadly and
uniformly rounded except above where the curve turns rather sharply into the hinge
line. Ventral margin rounded in front, straight and sloping upward in the posterior
half to the acute extremity. Posterior margin short, apparently straight and
sloping forward, cardinal margin straight, except for a slight prominence in the
region of the beaks. Anterior half of surface marked with closely arranged,
thread-like, concentric lines, between which small puncte are obscurely visible
on the specimen described. These markings seem to be wanting in the posterior
half, only a few obscure growth lines being visible here. Posterior ridge sharp
and strong, very gently curved in its course from the beak to the produced
lower angle of the posterior extremity of the shell. Between this ridge and a line
drawn vertically across the shell from the beaks, the surface is depressed, forming a

616 THE PALEONTOLOGY OF MINNESOTA.

[Technophorus divaricatus.

widening shallow sulcus and the straightening of the ventral margin. Postero-
cardinal slope concave, narrow, descending rather rapidly, not well preserved in the
specimen. Interior unknown; shell substance very thin.
Length 21 mm., hight 12.5 mm., greatest convexity (of a left valve) 2.5 mm.
Formation and locality—Upper part of the middle third of the Trenton shales near Cannon Falls,

Minnesota. It is associated with Plethocardia wmbonata, Ctenodonta planodorsata, Matheria rugosa and
other shells characterizing this horizon.

TroHnopHorus DivARicAtus Ulrich.
PLATE XL, FIGS. 37 and 38.
Technophorus divaricatus ULRICH, 1892. Amer. Geol. vol. x, p. 192.

Shell small, moderately convex, elongate, the length a little more than twice the
hight. Beaks small, scarcely projecting above the hinge line, situated about one-
third of the entire length from the anterior extremity. Dorsal margin nearly
straight, (faintly concave on each side of the beaks) about three-fourths as long as
the shell, terminating abruptly where it joins the concave posterior edge, with the
upper part of which it forms an angle little short of 99°. Anterior end a little higher
than the posterior, strongly rounded in outline, especially above; below rounding
neatly into the at first gently convex, then straight and finally concave basal line.
Posterior ridge thin but very prominent, curving slightly in its course from the beak
to the sharply produced postero-basal angle. Surface uniformly convex and marked
with fine, thread-like concentric lines in the antero-basal three-fifths beyond which
it first descends into a sulcus and then ascends sharply to the summit of the ridge,
dropping on the other side even more abruptly into the wing-like postero-dorsal part
of the shell. On each side of the posterior ridge there are distinct divaricating lines,
twice as strong as the concentric lines on the anterior part of the shell. They join each
other on the ridge, while those on the lower side of the latter meet the concentric
lines at angles of about 70°. Finally there is another set of such lines along the dorsal
edge, running parallel with the set on the lower side of the ridge. Under a magni-
fier, with certain lights, these lines appear as though minutely crenulated. Internal
characters unknown; shell substance very thin.

Length 12.5 mm., hight at the beaks, 5.8 mm., hight at posterior end of hinge,
5.1 mm., greatest thickness of closed valves, 4.1 mm.

Casts of the interior would be distinguished by having the dorsal and ventral
margins more nearly parallel than is the case in any of the other species referred to
the genus, except 7. punctostriatus of the Cincinnati. group, which is, however, a
shorter shell, and widely different in other respects. With the shell in a good state

LAMELLIBRANCHIATA. 617
Allodesma.]

of preservation the species is distinguished from all Silurian lamellibranchs by the
peculiar surface ornamentation.

Formation and locality—Near Cannon Falls, Minnesota, in the upper third of the Trenton shales.

Family CYCLOCONCHID A, Ulrich.

A full description of the typical genus of this family, and of several species of
same, will be found in vol. viii of the reports of the Geological Survey of Ohio.

Genus ALLODESMA, n. gen.

Modiolopsis (part.), ULRIcu, 1892, Nineteenth Ann. Rep. Geol. and Nat. Hist. Sur. Minn., p. 226.

Shell small, transversely elongate-elliptical, moderately convex; beaks anterior,
small, surface with concentric lines of growth. Hinge apparently with one or two
long posterior lateral teeth in each valve, two cardinal teeth in the right valve, and
only one in the left; anterior laterals short or wanting. Anterior adductor scar
distinct, large, ovate, margined on the inner side by a strong curved ridge extending
downward from the hinge at a point immediately in front of the beaks. Just above
the adductor impressions and in front of the ridge, a small pedal muscle scar.
Posterior adductor impression faint, larger than the anterior, of rounded form, situ-
ated near the middle of the posterior cardinal slope. Pallial line simple.

Type: A (Modiolopsis) subellipticum Ulrich.

The species upon which the genus is founded has really no relation to Modio-
lopsis with which I provisionally associated it. The original type gave no hint of
the character of the hinge, or I would never have thought of the arrangement first
adopted. A better specimen, recently collected, at once led to comparisons with the
very different genus Cycloconcha, Miller, and proved that the relations of the shell
were really with that genus. The only features wherein A//odesma differs from
Cycloconcha, so far as data now at hand will admit of judgment, are first, the more
elongate form of the shell; second, the anterior position of the beaks; third, the
curved ridge forming the inner border of the anterior muscular scar, and fourth, the
shortness or entire absence of anterior lateral teeth in the hinge. These differences,
though certainly of generic value, are not, as it now appears, of sufficient importance
to exclude the new genus from the Cycloconchide.

ALLODESMA SUBELLIPTICUM Ulrich.
PLATE XLII, FIGS. 9—14,
Modiolopsis subelliptica ULRICH, 1892. Nineteenth Ann. Rep. Geol. and Nat, Hist. Sur. Minn., p. 226,

Shell small, elongate-elliptical in outline, the length about twice as great as the
hights ends almost equally rounded, base broadly convex, cardinal outline more

618 THE PALEONTOLOGY OF MINNESOTA.
[Rhytimya.

gently arcuate. Beaks small, incurved, projecting but little above the hinge, situated
about one-fifth of the entire length from the anterior extremity; umbonal ridge
rounded, not strong, distinguishable chiefly in the upper third of the shell, where it
causes a flattening or slight concavity in the slope to the cardinal edge. Sides of
valves moderately convex, with point of greatest convexity a little in front of and
above the middle.

Casts of the interior exhibit a strongly defined ovate anterior muscular scar,
bounded upon the inner side by a distinct linear depression which must have been
produced by an internal ridge in the valves extending downward from the hinge
just in front of the beaks. Immediately above the adductor impressions there is a
minute but distinct pair of, presumably, pedal muscle scars. Posterior adductor
impressions very faint, rounded, situated a short distance within the middle of the
post-cardinal margin. Pallial line not very well defined, simple. Dorsum of cast
exhibiting impressions of cardinal and lateral teeth, indicating a hinge as shown in
figs. 13 and 14 on plate XLII.

So far as known the beds from which this species was obtained contain no
lamellibranch with which it is at all likely to be confounded.

Formation and locality —Galena shales near Cannon Falls, Minnesota.

Family PHOLADELLID, Miller.
Genus RHYTIMYA, Ulrich.

Orthodesma, WHITFIELD, 1878. Jour. Cin. Soc. Nat. Hist., vol. i, p. 139; MrEr, 1881, idem., vol. iv,
p. 76. (Not Orthodesma, HALL and WHITFIELD, 1875, Pal. Ohio,
vol. ii, p. 93.)

? Sedgwickia, WHITFIELD, 1878. Jour. Cin. Soc. Nat. Hist., vol. i, p. 140. (Not Sedgwickia, McCoy
1844, Synop. Carb. Koss. Ireland, p. 61.)

Shell elongate, moderately ventricose, the dorsal and ventral margins subparallel,
gaping slightly at one or both ends. Beaks rather prominent, situated from one-
third to one-fifth of the entire length behind the anterior extremity; posterior
umbonal ridge rounded, never very prominent; mesial sulcus wide, generally very
shallow, often however causing a sinuosity in the ventral margin. Lunule very
narrow, true escutcheon wanting, ligament external, attached to the edges of the
valves, extending the greater part of the hinge line posterior to the beaks. Hinge
apparently edentulous, test very thin. Muscular and pallial attachments exceedingly
faint, not satisfactorily observed; posterior scar large. Surface marked with
unequal concentric lines and furrows, gathered into a series of strong folds on the
anterior end. On the posterior half or more, the ventral part especially, the concentric
lines are crossed by closely arranged radiating series of small granules or spines.

Type: Rhytimya producta n. sp.

LAMELLIBRANCHIATA. 619
Rhytimya sinuuta.]

This genus is placed with much confidence into the same family as Hall’s two
Devonian genera Pholadella and Cimitaria and the Carboniferous genus Allorisma,
King. It is with the latter, however, that the implied relationship is easiest estab-
lished. The general expression of the shells is not much unlike in the two genera,
and in both the surface is grano-lineate and concentrically plicated; but here we
find one of the peculiarities of the Lower Silurian genus. In the latter, namely, the
folds are, when not entirely restricted to the anterior end, at any rate always the
strongest there, while in Allorisma they are strongest in the umbonal and central
parts of the valves. The hinge and the muscular impressions also, in the absence of
any knowledge to the contrary, are believed to be very nearly the same in the two
genera. The principal difference probably is the absence of a lanceolate escutcheon
in Rhytimya. A well defined escutcheon is developed also in Pholadella and Cimi-
taria and these genera are further distinguished from Rhytimya by their large
umbones.

In having the concentric surface markings strongest on the anterior end, these
shells agree with Sedgwickia, McCoy, founded upon Carboniferous species. But after
a careful comparison with the figures and descriptions of the species which McCoy
himself placed under that genus, I am quite couvinced that the Lower Silurian
types are not congeneric with the Carboniferous forms. There would be equally
good reasons for including them in the same author’s genus Sanguinolites.

With the exception of R. sinuata, which is from the middle Galena of Minnesota
and next described, the genus is known only from the rocks of the Cincinnati group.
The total number of species known is nine. Of these six are new and three have
been described and referred to other genera, namely, 8. A. Miller described one under
the name of Orthodesma byrnesi, and Whitfield two under the names of Orthodesma
mickleboroughi and Sedgwickia lunulata.* The original of the last species has a well
developed lunule and is much shorter than any of the other species. But it is evident
that the specimen has been much distorted by pressure. Descriptions and figures of
all the Cincinnati species except 2. lunulata are to be published in vol. vii of the
reports of the Geological Survey of Ohio.

RwYTIMYA SINUATA, 2. Sp.
PLATE XXXVI, FIGS. 46 and 47.

Shell rather small, about 25 mm. long, 12 mm. high at the beaks, and 11.2 mm.
across the posterior end, with the thickness very nearly equalling the hight. Car-
dinal outline declining anterior to the beaks, slightly sinuate posterior to them;

*A recent examination of Billings’ originaltypes of Canadian Lower Silurian Lamellibranchas proves that his Cyrtodonta
emma, from the Hudson River rocks of Anticosti, is really a species of Rhytimya. It is closely related to R, sinuata and
R. producta,

620 THE PALEONTOLOGY OF MINNESOTA.

[Cuneamya.

ventral margin broadly sinuate in the middle, gently convex on each side of the
center; posterior margin very slightly oblique, strongly rounded; anterior end sub-
rectangular, most prominent about the middle of the hight, the upper half nearly a
straight slope to the beaks, the lower rounding backwards into the base. Beaks
strongly incurved, situated almost a third of the entire length from the anterior
extremity; umbones large and prominent, constricted by the mesial sulcus which
crosses the valves and produces the sinus in the basal line. From the strongly con-
vex posterior umbonal ridge the surface descends abruptly to the cardinal margin.
Lunule larger than usual, of moderate depth and definition. Surface markings
obscure on the cardinal slope of the cast studied, on the umbones and flanks, con-
sisting of somewhat irregular, shallow, concentric furrows and fine striz. On the
anterior end these markings are strengthened or gathered into about twelve strong
folds, terminating at the margin of the lunule, and increasing regularly with the
growth of the shell. In having a large lunule, comparatively long anterior end, and
unusually prominent umbones, this species approaches ft. /unulata Whitfield, sp., and
reminds somewhat of Pholadella, Hall. The characters mentioned readily distinguish
the form from all the other species now referred to Rhytimya. Of associated shells
only Cuneamya truncatula has a concentrically furrowed surface but that species differs
too widely in other respects to be confused with R. sinuata.

Formation and locality —Middle Galena near Wykoff, Minnesota.

Family GRAMMYSIIDA, Hall.
Genus CUNEAMYA, Hall and Whitfield.

Cuneamya, HALL and WHITFIELD, 1875. Pal. Ohio, vol. ii, p. 90.

Thin, fragile, closed, bivalve shells, with ventricose valves and strong, prominent
incurved beaks, situated but little behind the anterior extremity; outline varying
from subcircular to somewhat elongate subrhomboidal; cardinal line very nearly
straight behind the beaks. Hinge linear, edentulous: valves probably held together
at the hinge solely by an external ligament. Cardinal margin of valves inflected,
forming a long escutcheon or false area posterior to the beaks; anteriorly a lunule,
varying considerable in depth and shape, but always well defined, is situated beneath
the beaks. Muscular and pallial impressions too faint to be determined with cer-
certainty. Surface marked by more or less distinct concentric plications or
wrinkles, which are usually rather obscure on the cardinal and posterior slopes and
always the most regular and distinct on the anterior side of the umbonal region.
Occasionally the surface is nearly smooth. An undefined, broad and shallow mesial

sulcus usually present.

LAMELLIBRANCHIATA. 621

Cunearoya.]
Type: Cuneamya miamiensis Hall and Whitfield.

This genus is represented in my cabinet by no less than sixteen, mostly unde-
scribed, Lower Silurian specific forms, all of which, saving the two about to be
described, were found above the top of the Trenton at Cincinnati and other localities
within a radius of forty miles from that city. Several of these species are represented
by casts of the interior in as fine a state of preservation as could be desired, and yet
in no case was it possible to reach any satisfactory conclusion respecting the
character of the muscular and pallial impressions. Under the circumstances it is
not unlikely that the claim of the authors of the genus that the pallial line is simple,
may be nothing more than the expression of their opinion and not the record of an
observed fact. In their description of the genus Hall and Whitfield state also that
posterior to the external ligament “the margins of the valves overlap each other to
the extent of the cardinal line.” This may be true of the specimens studied by them
but, except in several cases where it is evidently the result of accident or compres-
sion, it is certainly not true of any specimen seen by me that is sufficiently perfect
to admit of judgment on the point. The statement, therefore, wants confirmation
before it can be accepted as a fact. So far as my own observation is concerned, |
am obliged to dissent from such a view, especially as regards C. miamiensis the type
of the genus, of which several specimens that seem to have retained the valves in a
perfectly normal relation, have the escutcheon divided equally by the straight con-
tact margins of the valves.

As regards the external ligament, it is preserved by only two specimens seen by
me. One of these belongs to C. curta Whitfield, the other to C. coriformis Miller. It
is elongate (almost linear), occupies about one-third of the width of the escutcheon
and extends from the beaks backward a little more than one-third of the length of
the escutcheon. The same specimens preserve also something like a ligament over
the margins of the valves in the lunule.

The affinities of the genus are almost certainly with Grammysia as that genus is
defined by Hall in his great work on Devonian Lamellibranchiata (Pal. N. Y., vol. v,
pt. 1, pp. xxx and 358-354.) The principal difference between the genera as now
recognized lies in the hinge, this being weak and edentulous in Cuneamya while it is
stronger and presents one or two cardinal folds in at any rate the typical forms of
Grammysia. Shells probably belonging to this genus have been referred to Sedg-
wickia and Leptodomus, but as it seems, upon very insuflicient grounds, the types of
those genera, as defined by McCoy in 1544, (Synopsis Carb. Foss. Ireland) being of a
widely different nature. The new genus Saffordia is distinguished by its peculiar
hinge, much smaller beaks, and strongly defined anterior muscular scar,

622 THE PALEONTOLOGY OF MINNESOTA.

(Cuneamya truncatula.
CUNEAMYA TRUNCATULA, 1. Sp.

PLATE XXXVI, FIG. 39.

Shell of medium size, transversely somewhat elongate, the two ends of nearly
equal hight, with broad, compressed, nearly terminal, prominent and incurved beaks;
postero-cardinal region subalate, escutcheon less than half the length of the hinge.
Cardinal and basal margins diverging slightly posteriorly ; anterior end truncate,
almost vertical, the upper two-thirds sharply inflected, forming a rather narrow,
deep, and unusually long lunule, from whose lower end the outline slopes abruptly
backwards into the basal line; the latter is gently convex in the posterior half,
straight or very slightly sinuate in front of the middle, very obtusely angular in the
anterior third, and straight again when it ascends from the antero-basal angle to the
lower extremity of the lunule; posterior margin somewhat produced and strongly
rounded in the lower half, and very obliquely subtruncate in the upper. Posterior
umbonal ridge rather prominent, strongly rounded, not angular, curved and becom-
ing almost obsolete in the posterior third of the shell; cardinal slope concave, very
abrupt near the beaks; a narrow but distinct anterior umbonal ridge descends at
right angles to the hinge line from the beak to the antero-basal angle; between it and
the edge of the lunule a narrow sulcus; behind it a small well marked mesial sulcus
out of which the surface rises more gradually to the summit of the posterior umbonal
ridge. The most prominent point of the surface of the valves is situated on this
ridge somewhat above the middle of the hight and about two-fifths of the length
from the anterior extremity. Surface marked with nearly equal concentric undula-
tions or ridges. These are strongest in the mesial sulcus, somewhat ffattened yet
distinct in the anterior sulcus, and nearly obsolete on the cardinal slope. Hinge and
muscular impressions undetermined.

This species is closely related to C. coriformis described by, Miller from the mid-
dle beds of the Cincinnati group of Ohio. So far as known C. truncatula never attains
the size of mature examples of that species, while its posterior end is higher, the
escutcheon much shorter, the basal outline more convex, and the anterior umbonal
ridge narrower and much less prominent. In C. coriformis the point of greatest
convexity is on the anterior ridge while it is on the posterior ridge in the Minnesota
species. The surface markings also are coarser, and the mesial sulcus deeper in the
former.

Formation and locality.—Middle Galena near Wykoff and Pleasant Grove, Minnesota,

LAMELLIBRANCHIATA. 623

Cuneamya oblonga. ]
CUNEAMYA OBLONGA, 7. Sp.

PLATE XXXVI, FIGS. 40—41.

This species is very much like C. truncatula, differing from it chiefly in the follow-
ing respects: The anterior end is more rounded, the !unule shorter and smaller, and
the posterior end a trifle narrower and much less oblique, being almost vertical; the
hinge line is longer, terminates posteriorly more abruptly and is nearly parallel with
the basal margin.. The posterior umbonal ridge is less narrowly rounded, the mesial
suleus about the same or slightly deeper, while the part of the shell in front of this
sulcus, is practically without the anterior sulcus which is such a characteristic
feature of C.truncatula and C.coriformis. This sulcus however is indicated by a slight
flattening of the anterior slope. Finally, the surface corrugations are a grade finer.
C. miamiensis H. and W., is similarly marked but has a different outline and much
less distinct mesial suleus. In the matter of outline C. seapha H. and W., another
Ohio species, agrees more nearly, but in that species the lunule and escutcheon are
both wider and longer, and the surface markings quite different from those of C.
oblonga.

Formation and locality.—Galena limestone, Dixon, Illinois.

Genus SPHENOLIUM, S. A. Miller.
Sphenolium, 8. A. MILLER, 1889. North Amer. Geol. and Pal, p. 513.

Shell of medium size and larger, thin, strongly ventricose, very inequilateral,
elongate, occasionally with subparallel dorsal and ventral margins, but usually much
the highest posteriorly. Beaks incurved; umbones prominent, large and full;
umbonal ridge strongly rounded or subangular. No mesial depression or sulcus.
Lunule present, usually small and sometimes not sharply defined; escutcheon prac-
tically wanting. Surface concentrically lined; occasionally also with radiating
strie. Ligament probably both internal and external. Hinge apparently edentu-
lous; muscular scars very faint, not determined with certainty.

Type: 8S. (Orthodesma) cuneiforme S. A. Miller.

Too little is known of this genus to determine its affinities with any thing like
certainty. So far as the known characters admit of judgment they indicate relations
with the Grammysiide and the Pholadellide. Dr. Miller places the genus near
Orthodesma, but in this he is undoubtedly in error.

The two Trenton species following are perhaps not strictly referable to Spheno-
lium, being too narrow posteriorly. In all other respects, however, they agree well
enough with the more typical species of the Cincinnati rocks. Besides, I believe I

624 THE PALEONTOLOGY OF MINNESOTA.

[Sphenolium parallelum.

have evidence to show that this disproportionate development of the posterior end
was a gradual process, an undescribed species from the Utica horizon at Cincinnati
being intermediate in this respect between the Trenton forms and those occurring
in the middle and upper beds of the Cincinnati group.

SPHENOLIUM PARALLELUM, 7%. Sp.
PLATE XXXVI, FIGS, 42 and 48.

Shell elongate subovate, rather strongly convex, the thickness, hight and length
respectively as one is to one and two and one-fourth. Dorsal margin straight, nearly -
parallel with the ventral, terminating posteriorly in an obtuse angle where it joins
the obliquely rounded posterior margin; anterior end short, apparently narrowly
rounded; basal line very gently convex; posterior end rather abruptly rounded in
the lower half. Beaks prominent, full, incurved; umbonal ridge strongly convex,
somewhat emphasized by a slight furrow immediately above it in the cardinal slope;
another obscure furrow borders the dorsal edge. A small but well marked lunule
in front of the beaks, and a narrow and rather illy defined channel behind them.
Central and anterior parts of valves rather strongly convex. Surface marked con-
centrically with very fine striz and afew more or less obscure undulations. The
latter are more distinct and regular on the umbonal ridge than elsewhere.

The subparallel margins distinguish this species from the more typical forms of
the species described by Miller from the Cincinnati rocks.

Formation and locality.—‘ Lower Blue” beds of the Trenton formation, Mineral Point, Wisconsin.

Mus. Reg. No. 8346.

SPHENOLIUM STRIATUM, , Sp.
PLATE XXXVI, FIGS. 44 and 45.

The shape and general expression of this shell is almost exactly the same as in
the preceding, S. parallelum, yet when critically compared certain differences are
observed which render a separation necessary. The specimens are not very perfect
casts of the interior and exterior, still they preserve traces of very fine radiating
lines on the umbonal ridge and a few coarser ones on the cardinal slope which, if
such had been present on S. parallelwm, would undoubtedly show on the excellently
preserved cast upon which that species is founded. The Galena specimens again
present a number of small, regular and short concentric folds on the anterior end,
but they are wanting on the sides and posterior end where the folds are rather
distinct in the Lower Trenton species. In comparing the outlines a slight difference
is to be detected in the postero-cardinal region where, instead of being subangular

LAMELLIBRANCHIATA. 625
Salfordia.]

the margin is rounded in S. striatum. The four or five Cincinnati species known to

me are all much higher posteriorly.

Formation and locality.—Middle Galena, Goodhue county, Minnesota. The exact locality is about
thirteen miles south of Cannon Falls.

Genus SAFFORDIA, n. gen.

Shell rather small, transversely subovate, moderately convex, equivalve, very
inequilateral; back arcuate, beaks anterior, not large, curving obliquely inward and
forward; umbonal ridge moderate; between the ridge and the dorsal edge a more or
less distinct suleus. A sharply defined lunule beneath the approximate beaks, while
posterior to them there extends to the extremity of the hinge an equally distinct
escutcheon. Hinge plate thin, arcuate, with one horizontal wedge-shaped cardinal
tooth in the left valve which entered into a corresponding cavity in the under side
of the hinge plate of the right valve immediately behind the beak. Posterior half
of hinge consisting of a slender lateral tooth in the left valve and a corresponding
furrow in the right. Anterior to the center an elongate depression for the reception
of an internal ligament. Anterior muscular sear distinct, deep, subcircular, situated
beneath the lunule; pallial line simple, submarginal, posterior scar undetermined.
Test rather thick in the anterior part.

Type: S. ventralis, n. sp.

Beside the type, the Hudson River strata of Fillmore county, Minnesota, contain
another species having the characters ascribed to this genus. This I published
recently as a new species of Cuneamya, giving it the specific name sulcodorsata. It
is a more elongate shell but otherwise closely related to S. ventralis. A third species,
this one from the Galena, I described from. casts of the interior as Cypricardites ?
modestus.

The position of Saffordia seems to be near the Devonian Grammysia, the hinge
being similar in the two genera, though not by any means identical. In Grammysia
namely, as is shown in Hall’s work on the Devonian Lamellibranchiata (Pal. New
York, vol. v, parti, plate ivi, fig. 6), there is no cardinal tooth in the left valve as in
Saffordia, nor are the slender posterior lateral teeth represented. Another dis-
tinguishing feature of the latter, and one that is common to many Lower Silurian
shells, is found in the greater depth of the anterior muscular scar. In the genus
Cuneamya the hinge, aside from the escutcheon, is quite different, the test is very
thin, and the muscular impressions exceedingly faint, while the back, instead of
being arcuate, is concave behind the beaks, the latter being also tumid and much

more prominent.
—40

626 THE PALEONTOLOGY OF MINNESOTA.

(Saffordia ventralis.

Named asa small compliment to the veteran geologist, Prof. J. M. Safford, State
Geologist of Tennessee. Science is indebted to him for several most valuable works
on the geology of his state, while personally Iam under great obligations to him
for assistance in the way of specimens and advice.

SAFFORDIA VENTRALIS, ”. Sp.

PLATE XLI, FIGS, 34-41.

Shell transversely subovate, the hight and length very nearly as four is to five;
beaks small, declining, situated at the anterior extremity of the distinctly arcuate
dorsum, and projecting forward as far as the margin of the shell beneath it. Anterior
margin distinctly concave in the middle, the lower part narrowly rounded; ventral
margin rather strongly convex, posterior margin subtruncate, a little oblique, the
upper half straight or shghtly sinuate, the lower rounded. Surface of valves mod-
erately convex, with a very inconspicuous umbonal ridge between which and the
dorsal edge there is a shallow sulcus. Escutcheon well defined, extending the full
length of the hinge, in a dorsal view very narrow between the beaks, wide at the
middle, and narrowing again posteriorly. Lunule sharply defined, very deep, nearly
twice as long as wide. Surface marked by subimbricating concentric growth lines.
These are rather small but sharp and of nearly equal size for a short distance
beneath the cardinal edge, and only a few of them seem to cross the umbonal ridge.
Internal characters of hinge as shown in figures 37 and 41. Anterior muscular scar
of medium size, subcircular, deep, showing very prominently on casts of the interior;
pallial line and posterior muscular impression very faint.

This species is distinguished from S. sulcodorsata by its shorter form, terminal
beaks, and more rounded ventral margin.

Formation and locality.—Upper beds of the Hudson River group near Spring Valley, Minnesota, and
Iron Ridge, Wisconsin.

SAFFORDIA suLcoporsaTa Ulrich.
PLATE XLI, FIGS. 32 and 33.

Cuneamya sulcodorsata ULRICH, 1892. Nineteenth Ann. Rep.Geol. and Nat. Hist. Sur. Minn., D. 248.

Shell small, moderately convex, oblong-subquadrate, with the dorsal and ventral
margins subparallel and gently convex, the posterior end truncate, very slightly
produced and sharply rounded at the base, anterior end very short (long for the
genus), narrowly rounded. Beaks subterminal, declining forward, strongly incurved,
projecting forward rather than upward; umbonal ridge moderately prominent, not
angular. Dorsal slope with a distinct expanding sulcus; ventral and anterior slopes
gently and uniformly convex. Hinge line, posterior to the beaks, long, the edge

LAMELLIBRANCHIATA. 627

Saffordia modesta.]

inflected so as to form a well marked escutcheon. In front of and beneath the beaks
a deep lunule. Surface marked with regular, concentric folds, obsolete on the car-
dinal slopes, and by two or three times more numerous fine striw, which seem to,
have extended over all parts of the surface.

This neat shell was at first described as a Cuneamya, but with the discovery of
the closely allied S. ventralis it became evident at once that the species had been
misplaced. Compared with the type species it is found to differ in its form, the
dorsal and ventral margins being much less curved and the outline decidedly oblong
instead of rather broadly oval. The umbonal ridge also issomewhat better defined
and the anterior end of the shell projects beyond the beaks which is not the case in
S. ventralis.

Formation and locality.—At the top of the Hudson River group, Spring Valley, Minnesota.

SAFFORDIA MoDESTA Ulrich.
PLATE XLI, FIGS. 29—31.

Cypricardites? modestus ULRICH, 1892. Amer. Geol., vol. x, p. 100.

Shell small, moderately ventricose, obliquely ovate in outline, known from casts
of the interior only. In these the anterior end is very small, sharply rounded,
abruptly depressed beneath the beaks, projecting very little beyond them, and almost
entirely occupied by a subcircular muscular scar. Beaks small, only slightly incurved,
appearing prominent. Umbonal ridge scarcely distinguishable, the cardinal slope
faintly concave between it and another low ridge-like swelling that forms the back
of the cast. Along the hinge line there is a narrow impressed area. The lunule,
like the escutcheon, is proportionally narrower than in the other species. Shell
thin; hinge plate narrow, apparently with the characters (as shown by recently
obtained material) required by the genus.

As near as can be determined from casts of the interior only, this species would
appear to occupy an intermediate position between S. ventralis and S. sulcodorsata,
being longer than the first and shorter than the second.

Formation and locality.—Lower half of the Galena at Oshkosh, Wisconsin, and several localities in
Goodhue and Fillmore counties, Minnesota. ‘

628 THE PALEONTOLOGY OF MINNESOTA.

(Errata.

Lrrata for the Chapter on Lamellibranchiata.

PAGE,

477, 6th line from bottom, for Chenodomus read Cymatonota.

479, 3d line from bottom, for Clidoporus read Clidophorus.

479, 10th line from bottom, for usually read unusually.

479, 12th line from bottom, the variety referred to is described in vol. vii, Geol. Sur. Ohio, p. 629, as
Byssonychia vera Ulrich.

482. Supply omitted letters S-B to ends of bottom line of cut.

485, 14th line from bottom, for Hetenoptera, Ulrich read Opisthoptera, Meek.

486. The family LyRopDESMID& should be restricted to the typical genus, and Allodesma, Ulrich, referred
to the family CyYCLOCONCHID (next page) while Technophorus, Miller, and Ischyrina, Billings,
should follow as a distinct family, TecHNOPHORID a. (See p. 608.)

504, 17th line from bottom, refer AL. truncata Hall, to Modiolodon instead of Eurymya.

512, 9th to 14th line from bottom, dele remarks on Modiolopsis truncata Hall.

513, 5th line from bottom, for ACTINOMYA read WHITEAVESIA. It was learned too late to make
the corrections in their proper places that the name Actinomya had been preoccupied by
Mayer for a Cretaceous or Tertiary genus of shells. A new name is therefore necessary for
the Silurian genus, and it gives me much pleasure to propose Whiteavesia, after Prot. J. F.
Whiteaves, the successful paleontologist to the Geological Survey of Canada. The reader
will please substitute the new name for the other in the following places: Page 485, 4th line
from bottom; p. 501, 12th line from top; p. 504, 14th line from bottom; p. 505, several instances
in second and third paragraphs; p. 506, 1st line from top; p. 518, 5th line from bottom; p. 514,
several instances in third and fourth paragraphs; p. 515, Ist and 6th lines from top, and 4th
and 5th lines from bottom; p. 516, 5th and 7th lines from top; p. 517, 7th and 17th lines
from top; p. 518, 16th line from top; p. 524, 8th and 10th lines from bottom; and p. 531, 5th
line from top.

520, Ist line from top, after ORTHODESMA CANALICULATUM add n. sp.

563, 19th line from top, for 5100 read 8626.

592, 19th line from bottom, for CrENDONTA read CTENODONTA.

593, 9th line from bottom, for C. leveta read C. levata.

Figs. land 2.
1.

2.

Figs. 3 and 4.
Figs. 5 to 7.
5 and ‘6.

is

Figs. 8 and 9.
8.

9:

Figs. 10 to 14.
10.

1b

12.

13.

14,

Figs. 15 and 16.

Figs. 17 and 18.

Figs. 19 and 20.

Figs. 21 and 22.

Figs. 23 to 26.
23 and 24,

25 and 26.

Fig. PAG

Figs. 28 and 29.

Figs. 30 to 39.
30 and 31.
32 and 33.
34 and 385.

36 to 38.
39.

PLATH XXXV.

AMB ONY CHUA GB EIST RUATAC SEE we cleticrelets s wlovere aletepe tetas bls aictale cialevelsveltnicverere oicremstensieteje's
Nearly an entire cast of a left valve.
Anterior view of same, with the right valve supplied according to our idea of
the species. Middle ‘Galena, near Wykoff, Minnesota.

AMBONYGHIATPEANISMR DAMA SET clillsyctslateveisteny exots stats tate loiadeters i fat obebetak enete cobelateasiste falaletetete (atiers
Left side and anterior views of a specimen preserving the two valves partly
opened. ‘‘ Lower Blue” limestone, Mineral Point, Wisconsin.

JANTOOMNC SHUI AMINNIS} INES) OR po gnicsoo seo cinoad ooo NGddoN cooddsoow DoeNbadadsopsdaa

Lateral and anterior views of a well preserved fragment of the cast of a left

valve, showing very obscure concentric undulations, fine radiating strive and
the sharply defined subrostral lobe. Galena, Carroll county, Illinois.

An illy preserved cast of a right valve from the middle Galena at Weisbach’s
dam, near Spring Valley, Minnesota Survey Museum Reg. No. 8342.

AMBONY CHIASANEY GD AT TNVATe Ela lire ale ac, siekeselencietereredsrniete ior iogneratedusiheisi eee petereiseeieeretel siete
The cast of an imperfect left valve. The specimen has suffered from pressure,
reducing its diagonal diameter so that the anterior side curves too uniformly
into the base.
Profile view, the right valve ideal Lower Galena, Goodhue county, Minnesota.

CHIONY CHVAMITAM ET OSA ELAM ta cn pols stetevara ttvatohecracctete petal en elena laye cieveralee oleteloletete lstcistes ete cele

A small, but unusually well preserved cast of a left. valve showing the impres-
sions of the posterior adductor and pedal muscles, pallial line and ligamental
area. This specimen is precisely like those which Hall named A. attenuata,
but its less quadrate shape is evidently the result of pressure. Trenton lime-
stone, Minneapolis, Minnesota.

A left valve of the usual form from the ‘‘Lower Blue” limestone at Mineral
Point, Wisconsin.

Imperfect cast of a left valve preserving the muscular scars and a portion of the
wide ligamental area.

Anterior view of same, showing the impressions of the upper part of the margin,
the form of the beaks and the pallial line running down from it.

Cardinal view of same, showing scars of two small muscles (? pedal) behind the
beak. One or both of these scars are present in all the Ambonychiide. Lower
Trenton limestone, Beloit, Wisconsin.

CLION MG HLA SNUTID IAG Ms pS ie oisvacate one ne ait io wis <i sTatei ale Meee cE tee tee eroreeccia oe areata reacts

Lateral and anterior views of a right valve, showing the form of the species and

the comparatively fine and regular cencentric lines. Trenton limestone, Min-
neapolis, Minnesota. Survey Museum Reg. No. 5099.

GCLIONY CHEAT RR CTADEM all Ha eije.c eecceeeae sieve cage relies ice on lake em aiole stoleetinle eto sieve
Lateral and anterior view of a nearly perfect right valve. Trenton limestone,
Minneapolis, Minnesota.

CLIONVCHIUAS RH OMBOLD HAG WIT Chics -eisc 1 aictan eile lee als tla ol aiarelayoieieacte cieia citrate tateusi elo aieisiaeoetete
Lateral and anterior views of the specimen described. Trenton limestone, Min-
neapolis, Minnesota. Survey Museum Reg. No. 5526.

CLTONY CHTAS UND ATA MM ONS. cess lotctes vateietevets sini oval clarse see isietcleral eievakrelaveicieeieeteic cietere

Lateral and anterior views of an excellent cast of a right valve. Middle Galena,

near Wykoff, Minnesota. Collected by Dr. Robbins and now in the author’s
cabinet.

BYSSONYCHIA INTERMEDIA Meek and Wortinen:..........cecescccssccsccesscccncs
Anterior and lateral views of one of the original types of this species. Galena
limestone.
Cardinal and lateral views of a small but typical example from the middle
Galena horizon, near Wykoff, Minnesota.

PROLOBEBGAYSTRIATULAG Me PEN LSPs ne «ise. b-leleleelainerie cio ee eieeaeteen ie miseeyeteats
The left side of a specimen, showing the form and surface markings. Middle
Galena, near Pleasant Grove, Minnesota.

MODIOLODON( (2) (GIBB US;6M se SPi-[h occ sors cicielcreders els o'alsieinicisja, ct cleisie stemteratecavete wieivisicieetelsiaiersrere
The left side of a specimen of the natural size and magnified four and one-half
times. Upper third of the Trenton shales, near Cannon Falls, Minnesota.

ARISTHR ELAS NUTLD UL Ay We COMME DISD ies cictevaicre siofaceralavaiera oman tleye letra atuintaterajam cieiereiaiolerete

Left and right sides of an entire shell, x 4.5.

Lateral and cardinal views of the largest specimen seen, x 45.

Lateral and cardinal views of an internal cast, in which the hight is less and
the inequality of the valves greater than usual, x 4.5.

Natural size views of three shells. Middle third of the Trenton shales Chatfield,
Minnesota.

Outline view of a small left valve from the same horizon at St. Paul. In this
shell the anterior end is unusually narrow.

492

493

494

495

496

496

497

499

532

522

524

CEOMUGICAUM WD ALL RAURH ESTO REGS WRG Ak @O ravi iNESO1AG

} Lamellibranchiata | Plate XXXV.

Pee
y

Figs. 1 and 2.
Figs. 3 to 6.
3 and 4,

5 and 6.

Fig. if
Fig. 8.
Figs. 9and 10.
Figs. 11 and 12.
Figs. 13 and 14.
13.

14.

Figs. 15 and 16.
15.
16 and 16a.

Figs. 17 and 18.
Figs. 19 and 20.
19.

20.

Figs. 21 and 22.

Figs. 23 and 24.

Figs. 25 and 26.

7 and 28.
21.

Figs.

28.

Figs. 29 and 30.

PLATE XXXVI.

MODIOLOPSIS: SIMTLIS) WITCH oo << /sfeisie a tjein ot sislep cicle eles seas 00,08 alvlel tsiclebinz b= «=e ele riens
(See also plate xm, fig. 19.)
Dorsal and anterior views of the original type of the species.
the Trenton shales, Minneapolis, Minnesota.

Middle third of

IMODIOHOPSIS! ARGUILA, NASP. .'ela.2 sie.0 «0 pale cmc'ene cee since * cecjsine om\ssipe antes ona dea ciein
The right side and a dorsal view of a good cast of the interior. Middle third of
the Trenton shaies, near Fountain, Minnesota.
A smaller testiferous specimen, imperfect posteriorly, of the natural size and x 2.
Chatfield, Minnesota.

MODIOLOPSIS NANA, 0D. Sp.
Right side of a well preserved cast of the interior.
Minnesota.

Sere ee ee ee eee ee ee ro

Galena shales, Cannon Falls,

IMODIOEAPSIS AGe TEM OLDE ELA! lerrec cic ere eefeicinis = ofa ieiriniei on ise simacie re oieisle io al ciela ninteiniats
Cast of a left valve. Middle Galena, near Wykoff, Minnesota.

MODIOLOPSIS CHATFIELDENSIS, ND. Sp.
Right side of a cast of the interior, of the natural size and x 2. Middle third of
the Trenton shales, Chatfield, Minnesota.

MODIOLOPSISTOBSOG EIA Me: SP cjceisia cielo) fein ini ofolt iciera(ecleiniatelasts sje'ao eapicresla te Hoiinby eae
Testiferous left valve, of the natural size and x 2. Upper part of the middle
third of the Trenton shales, Goodhue county, Minnesota. ©

MODIOLOPSIS EX CEELENS)UaSPan fees 3\rnpte cilcip = hovel antes ose ola vies pio = ase biplane’
Cast of the interior of a right valve. The specimen is a little imperfect in the
anterior third. Geol. Survey Mus. Reg. No. 8374.
Well preserved fragment (anterior part) of a cast of the interior of a left valve.
Survey Museum Reg. No. 8375. Hudson River group, Granger, Minnesota.

MODIOLOESISICONCA VA UISIGDE jf ccije'id.o sopeice sue eee eerebecleemtees tone mintla cacomeiarniee
The specimen described, a testiferous right valve, of the natural size.
Lateral and dorsal views of same, x 2. Upper part of the middle third of the
Trenton shales, Goodhue county, Minnesota.

WHILRAYV ESTAVSUBCARENATA': TSSD -cpfeicals asteisitce ass's croton «ocala nie oi aanein gtde « -Aesmieee

The right side and an antero-dorsal view of a cast of the interior, showing the

form of the shell and obscure traces of radiating stri# on the posterior part.
Middle Galena, Goodhue county, Minnesota.

WHITEAVESIA MODIOLIFORMIS Meek and Worthen............2 ..eecceeceecccecs
The left side of an internal cast, Beloit, Wisconsin. Survey Mus. Reg. No. 8341.
View of the original type of the species. In the drawing the base and the ante-

rior end is restored and the right valve tilted, so as to give an exact dorsal

profile. ‘“‘Lower Blue” beds of the Trenton formation, Mineral Point, Wis-
consin. Illinois State Museum.
COLROMYA "DEMISSA, "T. AD resist facts stclorsreyole’(e lores a'o.s,s:atarw sis eles eels ouictoln sig ele aa seee erat

The nearly perfect shell upon which this species is founded; of the natural size
and x45. Middle third of the Trenton shales, Chatfield, Minnesota.

ORTHODESMA SUBNASUTUM Meek and Worthen ............ccccseccccereccceccess
Lateral and dorsal views of an entire cast of this species. Galena limestone,
Dixon, Llinois.

OR THODESMASSCHUCH MREt I SD torso sjotate cosines cata ees o1cnte clei du hes wat eeteels

Lateral and dorsal views of a cast of the interior, which is imperfect posteriorly,

but in good condition otherwise. Middle Galena, Fillmore county, Minnesota.
Survey Museum Reg. No. 8343.

FS MRNAS PICA AS FL AND SOY) moors mete tee ste ate 70 bela wlniare' #7574 n,n ja,0 Se sara ot aoeie Rise aE aisle ee
Interior of the left sai z as obtained ina gutta- percha impression of a cast of
the interior.
Hinge and anterior muscular scar of the left valve,
eters.

magnified nearly two diam-
Trenton limestone, Minneapolis, Minnesota.

UAT ETOAC ET COSA- WITICH: ox acwicianrs vice nae'en cic ceiclaninie talent - 20a See crelenin/enoeraenaatare
Views of the exterior and interior of a large right valve. Upper part of the

middle third of the Trenton shales, Goodhue county, Minnesota.
LOVER.

511

516

515

518

563

Figs. 3l and 32.
31.

32.
Figs. 33 and 34.

Figs. 35 to 37.

35 and 36.

37.

Fig. 38.
Fig. 39.

Figs. 40 and 41.

Figs. 42 and 43.
42.

43.

Figs. 44 and 45.

Figs. 46 and 47.

PLATH XXXVI.—Oontinued.

PSILOCONCHA- MINNESOTENSIS, Ms/SP>s.c ot ove.c's sicieiajs </e-sfoie wlslelore sicialasctaictefelele clecstelosie/-Ieia ie
The right side of a cast of thefinterior, which has been shortened by pressure no
less than is indicated by the outline restorations.
Dorsal outlines of same. Middle Galena, near Pleasant Grove, Minnesota.

HIN DODESMAMC UNDA UNTs 21 SPs ees c: srctersicinyals wtelialal er ofeverere| piciaeialolcicdelercleteseiet shalalalafniel setae siete
Dorsai and lateral views of an excellent cast of the interior. Middle Galena,
near Wykoff, Minnesota.

END ODESITAl COMPRESSUM (INS Pisis'o'sie oz 07s osoiw arstoia,ajeiefaier asia fe oiviniotel <daaeetstelateleisieveieleyeiere
Dorsal and lateral views of a cast of a left valve. Middle Galena. near Wykoff,
Minnesota.
Sectional view across the shell a short distance behind the beaks, showing the
inbending of the hinge plate.

ENDODESMAN UND OSUM EIS iS Die civecs cise crcitininversysicice etele dversinieieie scierohe oLetehe totale elalcisiciaiejaaie
Cast of the interior of both valves. ‘‘Upper Buff” beds of the Trenton formation,
near Beloit, Wisconsin. Geol. Sur. Mus. Reg. No. 8344.

CUNEANGYACTR UNG ATA SINGS IN aicle wis iolnistolere aelaletelejo\niate ei olaTerotetalereisiayeloharapsIeve(ro etal tensteteysralar
Cast of the interior of a right valve. Middle Galena, near Wykoff, Minnesota.

CUNEAMY-AT OBLONG Abney SP cietieierctacietaclactotsielsicie sisermouaisiele alt iereieloteiemsisinctete ataieterstatalsterats
Lateral and dorsal views of the specimen described. The imperfect posterior
end is restored in the figure. Upper Galena, Dixon, Illinois.

SPHENOLEU MG PAR AT MCT DMs olla (SP. ime cioteie vials cle taiztaretesereieratelsimierekeiers teeters cieyafohaiel one toreianerelarate
Cast of the interior of a right valve, imperfect at the anterior end, but otherwise
in an excellent state of preservation.
Cardinal view of the same, with the left valve restored in outline.
Blue” beds of the Trenton formation, Mineral Point, Wisconsin.
Mus. Reg. No. 8346.

SPHENOLIUMSTRIATUMs | SPiyess nies nieiciole eis crete cinysjerajahe| eels eleistelsjo<folels clsietwisja]oieteie(elteleials
Lateral and dorsal views of a nearly complete cast of the interior. Middle

Galena, Goodhue county, Minnesota.

“Lower
Geol. Sur.

REY TIMYA SINUATA, 1 SP oiseec cc cece scenes cr edesccinsne vices ccesesse eres csasensccnss
Lateral and dorsal views of an internal cast of a left valve. Middle Galena near

Wykoff, Minnesota.

529

529

624

624

619

DEO OCIUAN MR DVACL RAUHHISTORAESURG Mk OF IMiNVES DA AS

} Lamellibranchiata. | Plate XXXVI.

a ; b eo iW yal
See
ap

7 ’ oo)
Pe ay
~ :

- a
b co, ola
ae
—

preg a)

“.

on |
Per , ;
Dd ees ee
A ees
- Sets x dsl

ree TOTP eae
Mit ite Lie 28 > 4
) eel ee Bae

ae

Leen aks
eae
| pitts
« y "

|

ta ms i. +

a *
a oul
eine

oo =

ney
as A ee
Fy * am
un pal

Figs.

Figs.

Figs.

Figs.

Figs.

Figs.

Figs.

Figs.

Figs.

Fig.

Figs. 30 and 31.

Figs. 32 and 33.

Fig.

1 and 2.

3 and 4.

5 and 6.

12 to

15 and

17 to

20 to
20 to

25 to

14.

16.

19.

34.

PLATE XXXVII.

ENDODESMA ORTHONOTUM Meek and Worthen, Sp.......-:..ceeceeeet cone ceeeeees
Lateral and dorsal views of the original type of this species. The Baeenmien isa
good cast of the interior, in solid limestone, of a left valve. All of it is now
exposed, the tough matrix, which covered a considerable portion of the ventral
margin when it was used by Meek and Worthen, having been removed before
it was redrawn for the present work. Lower Trenton limestone, Dunleith,
Hlinois.
HINDODESMAsGESNIERT VUNG Sy S Piayretets ctete ls cteteletela\stek tos leletelenatatersierniaYetnlclenatelajeisietaeierieiainie
Lateral and dorsal views of a good cast of the interior of a right valve. Trenton
limestone, Ottawa, Canada. Introduced for comparison with the other species
of this proposed genus.

EX NDODESMAGPOSTIZA TUM, c1e8 Diese cisiclehs's wi ctavotels ese ail cfs ors nrsirete exeinle ereiersteners)otelolemtaseieter=

Lateral and dorsal views of an internal cast. Upper Galena, Dubuque, Iowa.
Geol. Survey Museum Reg. No. 8345,

ORTHODESMA CANALICULATUM, “1. SP. coe scicie ceieenis «te ts sine seein es 04 Siaiemiveisie «/eirlm els

The right side and a dorsal view of a nearly entire cast. Waynesville, Ohio.
Well preserved but incomplete cast, showing the anterior end and obscure rays

across the central half. Upper beds of the Cincinnati group, Waynesville, Ohio.

Posterior two-thirds of a cast from the Hudson River group near Spring Valley,
Minnesota. The length of this specimen was reduced by pressure, and to this
cause we must ascribe the more crowded arrangement of the radiating lines.

View of the broken end of same, showing the natural convexity of the valves

and the cardinal depression.

ORTHODESMA MINNESOTENSE Ulrich
The left side of the type specimen.
Dorsal view of same.

Anterior part of a dorsal view, x 4. Middle third of the Trenton shales, Minne-
apolis, Minnesota.

MODIOLOPSIS CONCENTRICA Hall and Whitfield. ...................0 cece e eens

Eero of the shell as obtained from a gutta-percha impression of a natural
mold.

Finely preserved cast of the interior. In offering these figures I wish it to be
understood that the specimens selected are strictly normal for the species as
it occurs in Ohio. Further, that the species is very constant, and that all
marked deviations in contour which may be observed in a series of Specimens
are the result of distortion through pressure.

{VEAN UX MIAT SA RTD ESO NUL Mtl Chas rcye eye. avaratascnese, sinalets ayer etctastrsunteyacatovere’s tre ilonn oier etch ag tare Tere
(See also plate xxXviil, fig. 45.)
Lateral, anterior and cardinal views of the pest cast seen. Trenton limestone,

Minneapolis, Minnesota.

MODIOLODON SEA U US 1s) SP) se: aera ele ose nit nlay ape eteretekaiayey ove iarefaratete isrcleyaiattiet=ttereVeterslete eiereteneTs
The left side and anterior and dorsal views of a cast. Lower or middle Galena,
Decorah, Iowa. Geol. Sur. Mus. Reg. No. 8363.
The left side of a cast of the interior from the Trenton at Danville, Kentucky.
A small specimen from the middle Galena of Goodhue county, Minnesota.

CrENODONTA-PLANODORSATA, (WITCH Yet semi wie seit cateerniels »<\aie oelelsie aetle siamiterenieies
(See also plate xu, figs. 38 to 40.)
Posterior view of the original type.
Right valve of same, with a small part of the surface magnified.
Profile in a postero-basal view

Cardinal view of same. Upper part of middle third of Trenton shales, Goodhue
county, Minnesota.

CTENODONTANCOMPRESS A SU Clie, 5 sepcrers res oie oi ets wicle/ote i oielaaveleneis aiotevalene ie evoke slereln ieee terse
(See also plate xxit, figs. 88 to 90.)

The original type of the species, x 1.3. Upper part of the middle third of the
Trenton shales, Goodhue county, Minnesota.

GCrENODONTA: TONGA. UIDICH oxides ccys ee ees wake SR aaa eis ote ce ee tate nsbonste eteraiielosie
Interior of the right valve upon which this species was founded, magnified twice
and of the natural size. Middle third of the Trenton shales, Goodhue county,
Minnesota.
CLIDOPHORUS 2 CONSUETUS WIT Chitin iain cictecitl-isieietetelel-1o'-spsiclecie ei ieciae ieraeheeaiae lotsa

The type specimen of the natural size and magnified twice. Middle Galena near
Wykoff, Minnesota.

TECHNOPHORUS, EX THNUATUS) (Wiliriehicyts erates specail ctevercisinietare c)eteleletetelelelere cters/oniieeteeters
View of the left side of the cast of the interior upon which the species was
founded. Middle third of the Trenton shales, Minneapolis, Minnesota.

CED MU CAC AUN OAC RAN AIS TO RGES ORT ERAT MIN VES DLAC

~ )
Le

amellibranchiata

Plate XXXVII.

+

«
ater ie
race

5 ,
ys ie)

re,

a Shwe he aa
<1 ae Srey vp be ney Thue oe

‘e a To —? bee ay Vag ‘
“ ths vat nog VY Nee ray La bs

Rete s
os ve im ba ay q eae a % hy pes

cy ee al '
“73

ve iW ies a
Het igs zd

yen
Ihe ‘i ar oe. +
ag gue } ress

aii cane Cire

Ny eo; i ny iD
ee Reh i fe
ta

es k

. 7
ao ul .
0 ne ™ nike

cae ligt ak ia ee > ee
4 is io ae sd ts. = wh ae oe at
to. a Caer, Ded
4, el ae. ) “9 ee
ee Deal te eas
~ gine Gat

Tiler
Later te ti aii ah

re
= al
_T

IN hte ear! “*

ae a A L aeein ; ; Sigel Te Saas Ah le ms ;

A

ae
~*~
to

Figs.

Figs.

Figs.

Figs.

Figs.

Figs.

Fig.

Figs.

igs. 33 and 34.

Fig.

Figs.

Figs.

Fig.

23 to 26.

24 to 26.

28 to 3l.

35.

36 to 38.

39 to 44,
39 to 41.

42.
43 and 44.

45.

PLATE XXXVIII.

VANUXEMIA DIXONENSIS Meek and Worthen ...............--e cece vere ee seer ecee
Lateral, anterior and cardinal views of a large cast of the interior. In many
specimens the anterior sulcus is deeper than in this one.
View of the interior of a right valve, as shown in a gutta-percha impression.
A smal! left valve which preserves a portion of the shell. Lower limestone of
the Trenton formation, Minneapolis, Minnesota.

WANUESE MLA “DDXONENSISs VATS INSUMDA' Mee WaTinnsisieleto cls crejatele sare elele'eyrercieier « eteisie
Anterior and lateral views of a perfect cast of the left valve. Trenton limestone,
Minneapolis, Minnesota.

VAAN UERENETIA GER, ODTUINGD ATUAN SEDAN SO arch afojeye vel sfeleieseisseletetstalecrerensre se vetvaeere) =talefels =iofekome etayote Voters

Perfect impression of the inner side of a rather large right valve. Geol. Sur.
Mus. Reg. No. 8319.

Lateral and antero-cardinal views of an entire cast of the interior.

Respectively, posterior, anterior, dorsal and side views of the cast of the interior
of a right valve of a small variety, differing from the usual form of the species
in the more evenly rounded surface of the casts and greater incurving of the
beaks. ‘Lower Blue” beds of the Trenton formation, Janesville, Wisconsin.

VANUXEMITA OBTUSERRONS) Wilrichy yet aiter-lejctelaseielviator/<lofeieiniclsiolelereterenels mia peje cle rctelete ntaatot sla
Side, anterior and dorsal views of a good cast of the interior. Lower Trenton
limestone, Minneapolis, Minnesota.

The hinge and an external.view of a specimen retaining a large part of the shell.
Dixon, Illinois.

VANUXEMTA/SUBERECTA,- TaSPra tisha e qaeincisoicctaie sci erties onitis: os ee cre eee arene
Three views, dorsal, side and anterior, of a good, though rather small, cast of the
interior. Trenton limestone, Beloit, Wisconsin. Geol. Sur. Mus. Reg. No. 8328.

NAGS Up- donut Renin Dy) Oy ala. in Sod omiec biome wucodGHontonobooeNDDoN demacaneaigebanbors
An internal cast of a right valve. Trenton limestone, Minneapolis, Minnesota.
Lateral, anterior and cardinal views of a specimen in which the right side is

preserved as an internal cast, while the other retains some of the shell.
Trenton limestone, Cannon Falls, Minnesota. -

AVZANTU ER MAS CRAIN SIA AEDES YD, ccehefatolaieystieve:c ste) ofollohsin-ccteneiets jejetalalevavelaia elaiereis telaierekel ietehaxe: aieeetear

A sharply defined impression of the inner side of a left valve. Middle third of
the Trenton shales, Minneapolis, Minnesota.

VANUKEMIA’ UBBON ADA, Ins (Sp sinensis seme ci elses stovelnveisicts n/a ioielarelettnietafel seerereraieiel etemstets
Four views of right valve of this species. 28, anterior; 29, the hinge; 30, cardinal;
and 31, lateral. Middle third of the Trenton shales, Minneapolis, Minnesota.

VANUXEMIA HAYNIANA Safford, sp

(See also plate xu, and page 479, fig. 36, Iv

)
A cast of the interior of a small right valve. Galena shales, Kenyon, Minnesota.

AVZANIUESG MAG ELEY EMOENGA TIS, «WL GE sayoyaro cach ats opere elerereletetele oral stetele ef cistevenslenesotcieiatela/ctete eiarepemstc

Anterior views of the two valves shown in fig. 34.

Casts of left and right valves of this species. The former was found in the
Trenton limestone at Minneapolis, and belongs to the collection of the Geo-
logical Survey, in which it bears the Mus. Reg. No. 5100. The latter is from
the same horizon at Cannon Falls.

IWANIUEE MEAS NTONAN (2ST 11) Wil GHlel Gey S plies ere ycterass otetwisiss ohalevelciesaiaateleletete eters leteveete eta
The left side of an entire cast of a rather small example. The anterior margin
seems to be more oblique than usual for this species. Trenton limestone

(2 “Upper Buff” beds), Rockton, Illinois. Geol. Sur. Mus. Reg. No. 8325.

WANUEGE MEAS SUBIR OT UINDD AYE ENS IS) = car ra-tarsls,> aoa loretaualesetetarste eietetole erafote<telatak erstelerere everiaterare
The interior of an imperfect right valve.
External view of a left valve, imperfect in the postero-dorsal region.
Outline cardinal view of the original of fig. 36. Upper part of middle third of
the Trenton shales_near,Cannon Falls, Minnesota.

WAG SAOp:G MOON WGI PON AIWAS Soh Clune qocooncans saoccde de 100 adsanod cans Gonanoosgooonyonae
Anterior, lateral and dorsal views of a nearly perfect cast of a right_valve. This
specimen is of the average size and proportions.
Cast of a large left valve that has suffered slightly from pressure, causing slight
differences in the outline and the anterior side to be less abrupt than usual.
Side and dorsal views of a smaller cast of a right valve in which the anterior end
is very obtuse. Middle Galena, Fillmore county, Minnesota.

WANUXEMIA (SAR DESONDE sUIGI CHI eisicv-y-ltuatrerelstase’a aretarcteie eenaiele ra atersteotereieasie nie steketeetetetchsteme

: (See also plate xxxvur, figs. 17—19.)

Interior of the left valve as brought out in a gutta-percha impression of the
original type of the species,

551

552

554

553

553

557

556

560

559

560

555

CLOMOGICON MORAG RAW AHESTORCES RGA KAO FMINNESUTAS

Lamellibranchiata { Plate XXXVII!.

fue

i aay Ee
mwiig y a :

mint lon mA

Be SG

Aa le, re uty.
My see

_ ‘ ine Ait
sae me os eae

ay
°
a — Hi %

Bras
ake ¥ 4h ? ;

ae hi ae
3 Mis Ve a
ies + ,
y met st ee ) Aes
e. 2

aM ie x" ed Pes

ee hee

pug bela pene

Al
ae
ws

a

a ae ae Ts

Figs

Figs.

Figs.

Figs.

Figs.

Figs.

Figs.

Figs.

Figs.

Fig.

Figs.

Figs.

Figs.

Fig.

PLATE XXXIX.

PaaE
Ust0t og SVAN UXE MLAS (DE OLPIENS, | TSP ioe sect acces aerate norris Sao eee teu ae siete 562
leetOntes: Lateral, dorsal and anterior views of the largest cast of the interior seen.
4 and ‘5. Side and dorsal views of a smaller cast of a right valve. Geol. Sur. Mus., Reg.
No. 8626.
Grand ei. DVANU XEMPAY WORDEN | WilTiChsae coe. cec ee eegecctete ices ok tie ce eee SornONe 561
The left side and an anterior view of a nearly perfect cast of the interior. Upper
Galena, Jo Daviess county, Illinois.
Sito 2s; CY RTODONTATOBESIA: GN nSDyeces as sees De fosetocstaue Oe PR iatmaioreic te Cela Plas ite Ina SPR Se 542
8 to 10, Three views of a typical shell of this species. Black River limestone, Mercer
county, Kentucky.
11 and 12. — A small specimen of the natural size and x 2, referred to this species with some
doubt. Middle third of the Trenton shales, St. Paul, Minnesota.
13) FOp 524 CTENODONTASGIBBERA SUS )\-.e.. -nefctynccin none = aieteistaceiah reclame Sere ena hiatus ee 542
Three views of the specimen described. It is a cast of the interior. Base of the
middle Galena, Goodhue county, Minnesota. Mus. Geol. Sur. Reg. No. 8366.
N6eto= 19 CVRTODONTAGRO TU ATA om, SPs. see Re eee cieiclomecinnciers sere een ome ere 541

16 and 17. Side and profile views of a large internal cast, from the middle third of the
Trenton shales near Fountain, Minnesota. Geol. Sur. Mus. Reg. No. 8336.

18 and 19. Two views of the testiferous type of the species. Black River limestone, Mercer
county, Kentucky.

20> tO=23.. _CYRTODONTA ABMINIS, Di sSD\ sacs: cee sees eee sve vs) State hurePeersiglay aves eeiate eeuatenttat ENT arches, aia - 540
20 to 22. Side and dorsal views, and the hinge of a right valve. Middle third of the
Trenton shales, Goodhue county, Minnesota.
23. A cast of the interior of the var. flllmorensis. Middle Galena, Fillmore county,

Minnesota.
2AtANGU29,. 1 CXR TOD ON TAS PIAR VA lon TSP iajeiaisiceicls intarsiaile aiated daevetele «i oarele or evsiatoie aa ets are een eee 541
The left side of an entire cast of the interior of the natural size and x 2.3.
Middle Galena near Fountain, Minnesota.
26faNde2ies CXYRTODONTA JANES VIL LENSIS, MSPs acinericisic elaieaisiesove cistern heer ante sioner erate aioe 537
Casts of a small right and a larger left valve. The central part of the surface in
the latter is broken in the specimen, but has been restored in the drawing.
“Lower Blue” beds of the Trenton, Janesville, Wisconsin. Geol. Sur. Mus.
Reg. No. 8323.
20) 00 dsandez4o, mi CYR TODONDA SUBOWAAN MSP /eiascacieaicie site ve sike cee oe eee eee noes 536
28, 31 and 32. Three views of an entire and well preserved shell. Birdseye limestone.
High Bridge, Kentucky.

29. An old left valve from the Black River limestone, or the base of the
Trenton of Mercer county, Kentucky.

30. Right side of a cast of the interior from the middle third of the Trenton
shales, St. Paul, Minnesota. ;

33. The hinge of a right valve from High Bridge, Kentucky.

45. A cast of the interior of a right valve which is doubtfully referred to this
species. The hight of the specimen has evidently been reduced by
pressure. Trenton limestone, Cannon Falls, Minnesota.

34) CYRTODON DAs AMPTPAR OM SSD tin are ence ak Sete clcine oa c A aes we eae ees S538

An imperfect cast of the interior of a large left valve. Trenton limestone,

Cannon Falls, Minnesota.
sorand 36.. CyYRTODONTA OBLIQUA Meek and Worthen... 2. 650.005. ose. cecceccicisaceeeeacice cle se 540
The left side and a front view of the original type of this species. Illinois State
Museum. Galena limestone, Scales Mound, Illinois.
37) Co) 405," | CYRLODONTACGLABHLE AN UIT Cla: « seyvereIeere ataciosleneioteesi on aetna are aire oe eters 543
37 and 38. Two views of the original type of the species. Middle third of the Trenton
shales, Minneapolis, Minnesota.
39 and 40. Two sharply defined internal casts of opposite valves, showing slight variations
in the outline. Trenton limestone, Beloit, Wisconsin.
Ale tO} 44 oe CYR TODON LAUPER SEMEL IS Mens Pinon clerk wis oles is0inve a ota folote tualo ane te eiare Persiataietann atente ee reetetere 544
41 to 43. Three views of an excellent cast of the interior. ‘‘Lower Blue” beds of the
Trenton formation, Beloit, Wisconsin.
44. A small right valve from the limestone at Minneapolis, Minnesota.
46> {CY RLODONTAOVIF ORMIS SUMED nus nic-tigts sees eels meietelan oiste 1e ohio me eateries 544

Mold of the interior of a left valve, with a portion of the shell remaining.
“Lower Blue” beds of the Trenton formation, Janesville, Wisconsin.

CEOMOGCICOUMWO NACL RAW SHISTO RAGS URGE WaOF) MINNESO RAS
) Lamellibranchiata |

Plate XXXIX,

—————

Fig.

Fgs.

Figs.

Figs.

Figs.

Figs.

Figs.

Figs.

Figs.

Figs.

Figs.

Figs.

Figs.

15 to
15 and

18 and

20 and 2

22 to

25 to

28 to

29 and

31 and

33 and

35 and

37 and

10.

11.

19.

24.

27,
30.
28.
30.

32.
31.

32.

34.

36.

38.

PLATE XL.

CYRTODONTAMOVAIROR MIS SUNT CH Aa ser-tonrerwiahe’s «cra eta crelelarare’s coneeey eee natetets tatete eit eta oraterecehe
(See also plate xxx1x, flg. 46.)
Anterior view of the type.

GYR TODON TWAS BIGEENG Sy, hsi8 Dylerclacutaisietsforciote arate inlore elesate\e eaeiaeto/ oe ietel eset asetoke ere) eee
Cast of a right valve from the lower Trenton limestone at Cannon Falls,
Minnesota.
Three views of the best specimen seen. Lower Trenton limestone, Dunleith,
Tllinois. oe
Another specimen from the preceding locality.

CXYRTODON TA: CINGUGAT AS UMELCH 5s aleicleix cis creat inivic aveie ane icielenele eaters see peromicisiciae ee carte
Anterior view and the right side of the original type. Middle third of the
Trenton shales, Minneapolis, Minnesota.

CYRTODONTA GRANDIS Ulrich, and varieties...................2. seeee sietiyecaiemectete
(See also figure 43, a-k, p. 547.)

Cast of a large right valve of the var. germana Ulrich. Galena shales, Goodhue
county, Minnesota.

Cast of a small specimen from the middle Galena at Lime City, Minnesota.
This specimen agrees better with the var. germana than with the typical
form of the species. Geol. Sur. Mus. Reg. No, 4102.

A small specimen (cast of a right valve) of the typical form. Middle Galena
Wykoff, Minnesota.

Interior of the original type of Cypricardites germanus Ulrich. Upper Trenton
near Danville, Kentucky.

Part of the interior of the var. luculentus Sardeson, as shown in a gutta-percha
impression from a cast of the interior belonging to the Survey collection.

A good cast of another right valve of the same variety and from the same
locality. Upper beds of the Hudson River group, Granger, Minnesota, Geol.
Sur. Mus. Reg. No. 8332.

ORV LODONWAGIDENN ESE Aer llitel Cintas etatel islet ctraeeeWelaseye¥elodeseietete ees icaatstetsielters te crete eneiete iets
Lateral and anterior views of a large right valve.
Hinge of same. The cardinal teeth are obscure in the specimen and may not be
exactly as drawn.
Anterior and lateral views of another right valve, differing from the preceding
in being more uniformly convex. Upper part of the middle third of the
Trenton shales, Goodhue county, Minnesota.

WSS hop-qonigd. wa 0. on py USP SENTING Pe oon oo dees rpcopnodonecndomeccn HeBEOoO. HonoodeD
(See also plate XXXvVIII, fig. ns and text p. 479, fig, 36—Iv.)
Imperfect interiors of two right valves, showing slight differences in the cardinal
teeth. Upper Trenton, near Danville, Kentucky.

PADI S(O UA DION Lop TONG UW AVAN AO a pooduGssnasis nadodedooonAcodagahccushaeenoosans
Three views of the type specimen. Upper part of the middle third of the
Trenton shales, Goodhue county, Minnesota.

IPENTHOCAR DEA SB ER EC TAcm Will CI. ves raters) slesclarsrereisraleterstenalelarctcteretelatlefeatehefeas liad sts tele tere reteye
Three views of the typespecimen. Galena shales, Goodhue county, Minnesota.

WHITELLA QUADRANGULARIS Whitfield, sp ..........-. 2 ++ se eeee eect eeee eee ee ee
An imperfect specimen doubtfully referred to this species. Hudson River group,
Spring Valley, Minnesota.
Dae and antero-cardinal views of a cast of the interior from Savannah,
1n01s,

WHERE A, OBLIQUADA UWI Chi sears, c. stereo felotecvne o cleiateioe cisreteversieactetetanslersieselaner teks atenaiieters

A cast of a left valve from the upper beds of the Cincinnati group, near Blan-
chester, Ohio.

The interior of a left valve, showing the hinge with its cardinal teeth, escutcheon
and posterior internal ligament supports, and faint muscular impressions.
The outline is imperfect posteriorly, causing the shell to appear less oblique
than it should be. Hudson River group, Spring Valley, Minnesota.

TRACHNOPHORUS SUB A CUMS a UML CI yeje15 oicietyesyetereneteleraieteneiateterchepata sDaterale <telapeteteletete tite tetate
Cast of the interior of the natural size and twice magnified. Trenton limestone,
Minneapolis, Minnesota. Geol. Sur. Mus. Reg. No. 8338.

THCHNOPHORUS MILISTR LAD US WUTC My aaleteia cc clee cre svaictalousiciele isle siolstessia iebele clareefaleleislere iets

Left valve of the natural size and a small portion of the surface enlarged to

show the regular character of the fine concentric lines. Upper part of the
middle third of the Trenton shales, Goodhue county, Minnesota.

TPECHNOPHORUSDIVARICAT US) UW lrl Chircicjorescateiasctotetels) tateve ele palelelereieve ol te teielelahetate le elatelsyaie) ala
The type specimen, a perfect left valve, of the natural size and enlarged two and
one-half times. Upper third of the Trenton shales, near Cannon Falls, Minnesota,

545

547

546

557

576

577

566

565

614

615

616

GEO GLU AMANWONVAC EAA HES TORRES ROE W@OraMINNESOLAG

Vol. III. } Lamellibranchiata { Plate XL.

Evy —
ima S Ler
oa

ars
Ss are
7 -ar

hee afte:

+ ae

. Ls
LDN ty ee
en Sy Sas a
“PO a a RU
Ay Pak i
ei Pils
’ wy ' id

"
n= Me

FT “x ia fal nes of ar bs i

tans ant ee ted
Re el ne

Y sth er a

Ue

‘a
oy. ww
ne ig

Cogn a*

Figs

Figs.

Figs.

Figs.

Figs.

Figs.

Figs.

bo

and 3.

4 and 5.

6 to 9.
6 and 7.

8 and 9.

- 10 to 14.
10 to 12.
13 and 14,

15 and 16.

17 to 21
Ate

18.
19 and 20.

21.

. 22 and ? 23.
22.
23.

29) tor sl:
29 and 20.

32 and 33.

34 to 41.

36.
37.
38.
39 and 40.

41.

27 and 28.

PLATE XLI.

PAGE.
WiHITELUGA UU GAMENA TSI). sle,staye tess oratars att bake «rose deteie sto eaiars) ctotaletomietnlonsrsvalereeyainre e arotoe 569
Left side of a cast of the interior. Middle third of the Trenton shales, Minne-
apolis, Minnesota.
WHILELDTA, CONCENTRIGA WiIrichix,,. 5 tetci- cos celslomteasirusaie cle sinicls aieietomiersta ioe emer: 569

The right side and a front view of the type. Middle third of the Trenton shales,
Minneapolis, Minnesota.

WHITELULACMEGAMBONA! WihIGHeld, (Speiee-ctece sors s/teciele eicy-tete 5 s)o.07s arsieibyoleie reine eer.
Two views, lateral and anterior, of a good cast of the interior. Trenton lime-
stone, Minneapolis, Minnesota.

WiHITHEIVAS COMPRESS AM OMET CH cH u's scrativs strettes operate iearelaene reticle ei centers
The right side and a front view of an internal cast, differing slightly from the
type of the species.
Two views, side and dorsal, of the original type of the species. Middle third of
the Trenton shales, Minneapolis, Minnesota. <

SWVC ESTE ACS ERIN CAT Ate UD ITSH C Hier sts scstevsjsyzinvctarcietes eave rats laveteisy «/ejcle ae ietatersTisieyisielerereicie stelctersss
Dorsal, side and front views of an average specimen.
The right side and a posterior view of the largest cast of the interior seen.
Galena shales, Goodhue county, Minnesota.

AVERITT AQSP RAs COLE UAUMU LCI japaiepreererstaran-tefeccielslotenty tasiaibisTersieeisienctsteriate HomeeadupuoCAnd
The left side and a dorsal view of a large and well preserved cast of the interior.
Galena shales, Goodhue county, Minnesota.

WHEREAS SCORTE TDL SU) Clg ais. ctersvayeyeake rs ietvoaturanteketey sieiclelelctcrey-siete’sereeretelstatstnl ener tlerete

A very large left valve from the middle third of the Trenton shales at St. Paul,
Minnesota.

Hinge of same. The cardinal teeth are abnormally developed.

Anterior and side views of the original type of the species. Middle third of the
Trenton shales, Goodhue county, Minnesota.

Hinge of same x 2, showing the cardinal teeth, the striated escutcheon and the
posterior internal ligament supports in a very satisfactory manner.

Win TRA SUB CAVRITINGAUIA coTN-c SI) >. nfetalevesetalere store cele tetensrererctoteletel iarsteler esatal cine ciarelatefetereiate tay

A well preserved internal cast of aright valve. Middle Galena, Wykoff. Minnesota.

Cast of a left valve, supposed to represent an earlier variety of this species.
Lower Trenton limestone, Jo Daviess county, [llinois.

WHT PE TIAUCVON TR IC OSA EVA LIS 1 cpay.tecrcrevreretaterelnotatarototetereterstaqere wie wistareleetctercraierciaiare shansters
Tnternal cast of a right valve in which the anterior margin is uniformly rounded.
Anterior view of same, with the left valve restored from another specimen.
Outline of the antero-dorsal part of a left valve in which the anterior margin is

sharply rounded above. Trenton limestone, Watertown, New York.

WHITELLA STERLINGENSIS Meek and Worthen ...............00seseeee sees sence

Antero-cardinal and lateral views of the original type of this species. The speci-

men is a cast of the exterior. Upper part of the Hudson River group, Sterling,
Tllinois. Illinois State Museum.

SABEORDIA= MODEST Ate WIL ClaWetetsarscrotcin tara olarersisvalece otavens clave stsyetayofe are: etelotatisierctexeralcraratatereieet ie

The left side and a front view of an entire cast of the interior, natural size.

The specimen is of the average size. Galena shales, Goodhue county, Minnesota.
The left side of same.x 2.

DAMKORDUAT SULCODORSATAY (WGC stereo steers iareuei<cteieralcleleisielo/o|ata)elsletsleaeete! oltehslstaistereteletareuet=
Antero-cardinal and lateral views of the specimen described, Upper part of the
Hudson River group, near Spring Valley, Minnesota.

SAERORDIAT VENDRVATIIS MI Sp erstveccss we vclozereleveieieyheperetsveterstarchevalabetot oleressiela wiaereheretetana cyevete Meters
Cast of the interior of a left valve. Spring Valley, Minnesota.
Gutta-percha impression of a natural mold of a small left valve in the base of a
bryozoan. Hudson River group, Iron Ridge, Wisconsin.
Anterior view of same.
Hinge of a right valve.
A left valve.

Anterior and cardinal views of same, with the right valve restored from the
original of figure 387. :
Hinge of the left valve. Upper beds of the Hudson River group, near Spring

Valley, Minnesota,

570

568

572

574

S71

572

573

567

626

CEOMU GLU AMMO AdL RAW THES LORGES RG ERAT IMINTES OTS

{J T Ear ae ,
Vol. Il. / Lamellibr anchiata |

Plate XLI.

|

—

Figs. 1 to 5.
land 2.

3 and 4.

5.

Figs. 6 to &
6.
Tand 8.

Figs. 9 to 14.
9 and 10.

Il and 12,

13 and 14.

Figs. 15 and 16.

Figs. 17 and 18.

Fig. 19.

Wigs. 20 to 25.
20 to 23.

ge

Figs. 26 to 28.
26 and 27.

28.
Fig. 29,
Fig. 30.

Figs. 31 to 33.
3L and 32,
33.

Figs, 34 to 36.

Fig. 37.

Figs. 38 to 40.

38.
39.
40.

Figs. 41 to 43.
41 and 42.
43,

Figs. 44 to 49.

45 to 47.

Figs. 50 to 52.

Figs. 53 to 58.
53 to 56.

PLATE XLIt.

PAGE.
LYRODESMA ACUMINATUM, De SPecce ce cece se ccccncsiccsccccconcenccrcnvctcncenereraccrsves soscsresnesseesscucaces 609
Lateral and cardinal views of a large rei valve of the typical form.
Opposite views, the inner X 2, of a left valve of the var. intermedia
The hinge of a right valve of the typical form, x 3, showing the retral sweep of the teeth.
LYRODESMA CANNONENSE, Nl. SP .....0-eeceeeceeeeeceees Bente Aev'cid Salute cis'e > wisicle os ot Datnaaailans seve sSnee VORAs shea ame 910

Somewhat weathered cast of the interior.
Lateral and cardinal views of a cast preserving the muscular scars.

AULLODESMA SUBELLIPTIOUM UIriCh....... 2.0006 scence eect ee cee e cece ce cee ctncenereneseseecenecsssseee ween shacks
Cardinal and lateral views of the cast of the interior upon which the species was founded.
Lateral and cardinal views of a better preserved cast, % 2. showing the muscular sears, pallial line
and impressions of the hinge teeth,
Restoration of the hinge.

MODIOLOPSIS OWENI, n. Sp Soetise ee
Lateral and cardinal views of a partial east of ‘the inter lor.

MODIOLOPSIS CONSIMILIS, Nn. SP - Raatideawiashe se winjo cin hes emacleavobaiy aauie<'s™ ko'epe
Lateral and cardinal views ofa an mentixe Silicified arent ‘of ‘this epaclas!

MODIOLOPSIS SIMILIS Ulrich ........ ss. .eeee
(See also plate x XXXV v1, ‘figs. I and 2 2 NE
View of the right side of the type of this species. The specimen is preserved chiefly as a cast of the
interior and shows an impression of the shallow anterior muscular scar,

CLIDOPHORUS NEGLECTUS Hall. berate (Sosananen == eo
Four views of a rather large eoaotaen oral the left side of. w which the ais has! been ‘removed, so as to
show the muscular sears and the strong vertical furrow left by the clavicle. The posterior extrera-
ity in this specimen is narrower than usual.
An oblique cardinal view of a cast of the interior, x 6, showing an impression of the denticulated hinge.
Very perfect cast of the interior of an unusually large right valve, showing, besides the usual char-
acters, several obscure rays on the sides and a number of small umbonal scars. Minn. Geol. Sur.
Mus. Reg. No. 7336.

CTENODONTA LOGANI Salter
Cast of the interior of a right valve. Minn. Geol. Sur. Mus. Reg. No. 8316.
Gutta-percha impression of same, showing the hinge.

s and other characters of the

CTENODONTA OVIFORMIS, 1. SP.cceee cece cece cece cece cnees ceeeaeeeeeeeees
Left side of a cast of the interior, showing the ‘strong muscular $s
species.

OTENODONTA NASUTA Hall .....cccces csccccccecncc ce seccescncccececscrcsscccccensenscsnacssucucsssssassecussesasee
A small testiferous left valve of this species from the middle third of the Trenton shales, near Cannon
Falls, Minnesota.

OTENODONTA CUNEIFORMIS, Nl. SP .s-e- ee ccee cece cece cece ce cece teeeencecccceeeean see sesssbaseeerscscesceesece sees
Two right valves, the first with the posterior constriction more distinct than in the other.
Hinge of a right valve, x 2

CTENODONTA SUBNASUTA, Dl. SP...cccec cee cece er csccenee sees ceccteseeeeeceescncnsanscaccusaceceeces acess arenes
Three views of a cast of the interior.

CTENDONTA GIBBERULA Salter.. GC ae Seddce se Utidticrs ¢fanucet [osive's\da\snpaesnaanee
(See ‘also text p. “599, fiz. ss, t and’ g)
An excellent mold of the interior of a left valve.

CTENODONTA PLANODORSATA Ulrich........ 0 ....+- a biaaysesly ta ae cee
(See also plate XXXvUI, figs. 25—28 )
View of the inner side of a left valve, x 3.
Hinge of same, more highly magnified.
Artificial cast of the interlor of a right valve.

CTENODONTA CARINATA, Ni. Sp.
A right and left valve, both inipertend and varying sligtly in outline,
Dorsal view of the left valve,

OTENODONTA NITIDA Ulrich ...... .22. cee ceceecceeees cece seneeereee tenaeecsnsassccsesaneeenssesaces ns ae
The right side of a small testiferous specimen,
Lateral, cardinal and posterior views of same, x 2
The right side of a well preserved cast of the interior of a large example.
Cardinal view of same, X 2, showing scars of the adductor and pedal muscles,

OTENODONTA MEDIALIS, .D. SP cc cece cocccesccccceccnccercceecesscteessnesnssee senrscesscessssenee Nias todas
Silicified right valve of the species from the middle third of the Trenton shales.
Hinge of same, X 2
Cast of the interlor from the Galena shales, provisionally referred to this species.

OTENODONTA SCORTELDY, De SP. .....ces cee ence ccccceccccscssceersenscnss secscces & do. cucwewa sie Vener ene ameter
The left side and posterior, anterior and dorsal views of a specimen preserv ie she shell and showlng,
among other characters of the species, the sharply angular umbonal ridge. Middle third of the
Trenton shales, near Cannon Falls, Minnesota.
Hinge of a rightWalve, 2.
The right side of a cast of the interior from the Galena shales, provisionally referred to this species.
The anterior end ts larger than In the typical form.

(Over.

617

g

Sul

584

580

592

Figs. 59 and 60.

59.
60.

Figs. 61 to 64.
. 61.
62.

63 and 64.

Figs. 65 and 66.

Figs. 67 to 73.

67 and 68.

69.
70 to 72.
73.

Figs. 74 and 75.
74.
75.

Figs. 76 to 82.
76 to 78.

79.

80.

81 and 82.

Figs. 83 to 87.
83 and 84.

85 to 87.
Figs. 88 to 90.

88 and 89.
90.

Figs 91 and 92,

Figs. 93 and 94,

Figs. 95 to 97,

PLATE XLII.—Continued.

PAGE.
OTENODONTA, SOCEATIS Met SD iiss cnc .ccicisicieiey nine v'sle (eis aisiaicie's\neininis «\sjalelaiaia Seba nSdoncoeeeaubsodenechmercisaac su agsoeor 594
Outline views of three specimens of different sizes and showing slight variations in form,
Hinge of two right valves, x 3, showing slight differences in the anterior parts.
CTENODQNTA CALVINI, n. Sp.. Sicess/ ental 4 weie is steeineta elon ats 596

An excellent cast of the interior of a left wae showing. sanecular scars sand rayeon more plainly “ine
usual. In this specimen the length aiso is a little greater than in the others.

Another cast of a left valve. Minn. Geol. Sur. Mus. Reg. No. 8628.

Lateral and cardinal views of a cast of a right valve, representing the usual characters of the species.

CTENODONTA MADISONENSIS, nl. Sp
The left side and an anterior view of a testiferous example of this species.

OTENODONTACHE OUND AGE All masareajnreinictatal=isisiiels sal aie o claleteinm hase sleintelt el \lelsieloieeielalee vie sialic he seelssaitioctcnlest: eiscisie sistent :
The right side and an anterior view of a cast of the interior. In many specimens the posterior
margin is more rounded
A small part of the external surface magnified to show the fine concentric and radiating lines.
Cardinal and anterior views and the right side of a specimen preserving the shell.
The wavy hinge line as shown on a Cast of the interior, x 5.

CTENODONTA SIMULATRIX, n. Sp . Socciks * Soc oon 5 5 saodLo
A cast of the interior of a right males Bromine ine ehanenian sears 5 andi ‘retaining a little of the shell
about the beak.
As much of the hinge as can be made out from the preceding specimen.

CTENODONTA ALBERTINA, TD. SP.......0---.e2 eee aise a tale clstoeicietatetolatcialeletia cals ota ciepeere sintete picts onan atetsiets incetensralalststal dosabecs
Three views of a large specimen having the posterior end a little narrower than usual.
A smaller specimen of the usual form.
Hinge of a large and smaller right valve, showing the subrostral pit and the geniculated teeth.
Cardinal and lateral views of a cast of the interior which retains a part of the hinge,

OTENODONTA OBLIQUA Hall. ..... ... Aran erin seco nase,taatacpen Sy aee ase o5 SO ABR OSE taaon oe ne acD OSS ub cacoad
Lateral and cardinal views of a small specimen of the large northwestern variety of this species, x 5.
As usual, the specimen is a cast of the interior and shows the muscular scars and impressions of the
hinge denticles very clearly.
Three internal casts of a small form of the species from the Cincinnati group of Ohio, x 5.

CTENODONTA COMPRESSA Ulrich ............+-- Scab bodicnoscceos Pekaricetie cieraeler Tes iotastainclole'stcinate’< thale'a ciniale leis) ctsiasieteete
(See also plate xxxvil, fig. 29.)
Posterior and lateral views of a left valve.
The greater part of the hinge of another left valve, X 5, showing the various parts in a beautiful
state of preservation.

OTENODONTA HAMBURGENSIS Walcott ..........02 cece cece cece cee e eee Gd sAnabosseage os
A right(?) valve of the natural size and X 5.

CTENODONTA ALTA Hall. mopeidoscnsos
Lateral and posterior views Sor a east of the interior:

OTENODONTA INTHRMEDIA) UIriGh >.< ccjs.ccteers = soninecle aleelsinc es cles nies siasceenan coc aakon aa

95 and 96. Lateral and posterior views of a right valve preserving much of the shell. The opposite valve is
restored in the profile view.
97. A sharply marked cast of the interior of a left valve. In this specimen the posterior extremity is
unusually produced, |
Figs. 98 to 101. OTENODONTA RECURVA Ulrich........... Semaidalaa ante mtearieieeioalas eileniesaieiesnisinanics Ca rocde cco ShbossoossGude
98 to 100. Posterior, lateral and cardinal views of a 3 pertect specimen of this species: showing the usual form,
the anterior sulcus and the sharply defined anterior and posterior lunettes.
101. The greater part of a hinge of a left valve, X 2, showing the arrangement of the denticles, the
sharply elevated outer margin and the ligamental area on the right side of the beak.
Figs. 102 to 106. CTENODONTA SIMILIS Ulrich.......... Secon: stecodLsacosas Se shasecg -danodeega Sanide
102. Hinge of a left valve of this Bpecies: x 2, ishowivg the puinicipal features upon which this species is
separated from C. recurva. (See fig. 101.)
103. The left side of a specimen, showing the usual form of the species. Minn. Geol. Sur. Mus. Reg.
No. 8368.
104 to 106. Lateral, cardinal and posterior views of a specimen having an outline very similar to that of

CO. recurva. But the absence of the anterior sulcus, the greater convexity of its valves and the
less sharply defined lunettes are all characteristic of C. similis and prove its distinctness from
C. recurva,

597

595

604

605

601

GCEOMOCICAUMMOVAI RAUBHISTORGES URGE @O revives DLS
) Lamellibranchiata | Plate XLII.

Vol. Il.

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Ww

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Z
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