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YALE PEABODY MUSEUM

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Number 74 March 31, 1968 New Haven, Conn.

REVISION OF THE TYPE SPECIES OF THE
ORDOVICIAN NUCULOID PELECYPOD GENUS
TANCREDIOPSIS

A. Lert McALESTER

ABSTRACT

The type species of the early Paleozoic nuculoid pelecypod genus
Tancrediopsis Beushausen, 1895, is shown to be Ctenodonta contracta
Salter, 1859, from Middie Ordovician rocks of southern Quebec, Canada.
This species is redescribed from a series of 189 well-preserved silicified
specimens, about half of which were collected at the original type locality.
This large sample permits the definition of limits of variation in the species
and reveals previously unknown morphologic features, among which are
strong pedal muscle scars and external escutcheonal perforations. ‘The
species is easily confused with closely related sympatric species of Tan-
crediopsis, and criteria are discussed for distinguishing it from these
similar forms. The correct name for “Ctenodonta” contracta Salter is shown
to be Tancrediopsis cuneata (Hall).

INTRODUCTION

This paper is the first in a projected series to be devoted
to generic-level revisions of the systematics and phylogeny of
Paleozoic nuculoid pelecypods. As a vital first step toward
clarifying the early history of this common and long-ranging
group, a restudy is being made of the type species of each ge-
neric name that has been proposed for Paleozoic nuculoids.

2 Postilla Yale Peabody Museum No. 74

This redescription of the generic type species is being patterned
directly on a study of Paleozoic gastropod type species which
has been compiled by Knight (1941). As in Knight’s work, it
is planned to make these redescriptions as objective as possible
by basing them only on known original specimens of the species
involved (see Knight, 1941, p. 1, for an excellent discussion of
the value of objectivity in such work). An exhaustive search
of the literature has indicated that about 60 names have been
proposed for Paleozoic pelecypod genera which have at some-
time been considered to show taxodont dentition or other ev-
idence of nuculoid affinities." The redescription of the primary
types of the type species of these genera is now about half
completed, and it is expected that these revisions will be sub-
mitted for publication as one unit within a year.

As a further step toward understanding the morphology,
adaptations, and phylogeny of Paleozoic nuculoid genera, a
much longer range program is planned for assembling and
studying additional non-type material of the type species of
many of these genera. In this program, particular emphasis
will be placed on genera that cannot be adequately understood
from the surviving original type specimens. Every effort will
be made to assemble enough material of each species to permit
the application of modern concepts of population systematics
for determining the true nature and variability of specific and
generic characters. It is planned to publish these more compre-
hensive revisions intermittently, cone genus at a time, as ad-
equate material of the type species can be assembled. This
paper is the first of this series of type species revisions based
on additional material that was not available to the original
author of the species. It treats the common Ordovician nu-
culoid genus T'ancrediopsis Beushausen (1895), whose type

1 The term “nuculoid” is used here in the broadest sense to include all
Nucula-like forms from Paleozoic rocks. In practice, this means all
Paleozoic pelecypods with taxodont dentition, because the convergent
development of such dentition in other unrelated groups, such as arcids
and the fresh-water genus J/ridina, did not take place until after the
close of the Paleozoic. As thus defined, “nuculoid” is approximately
equivalent to the Subclass Protobranchiata (other than the Solemyidae)
which has recently been suggested to include all pelecypods with proto-
branch ctenidia (see Cox, 1959).

Mar. 31, 1963 Revision of T'ancrediopsis 3

species, Ctenodonta contracta Salter (1859), has never been
adequately understood.

This revision of Ctendonta contracta is based on Salter’s
15 original specimens from the Geological Survey of Canada
collections, supplemented by an excellent series of 174. si-
licified specimens from the collections of the Yale Peabody
Museum. About half of these additional specimens are from
the original type locality of the species. The Yale material
was collected in the early years of this century by C. E. Beecher
and P. EK. Raymond as a part of an ambitious program of
restudy of important silicified early Paleozoic faunas of eastern
North America. Many hundreds of pounds of rock from several
localities were collected and etched, but the program was cut
short by Beecher’s untimely death in 1904, with the result
that this great wealth of material has never been studied. The
etched Middle Ordovician collections have now been sorted for
pelecypods and have yielded about 1500 identifiable specimens.
These collections are particularly rich in well-preserved nu-
culoid species, and it is expected that this material will provide
a basis for future studies on the earliest evolutionary radiation
of this important group of pelecypods.

I am most grateful to the National Science Foundation for
support of these studies of Paleozoic nuculoid pelecypods under
its Program for Systematic Biology, Division of Biological
and Medical Sciences (Grant No. G19961). I am also greatly
indebted to D. J. McLaren, T. E. Bolton, and G. W. Sinclair
of the Geological Survey of Canada for the loan of Salter’s
types and for generous cooperation on this project. Finally,
I wish to thank D. W. Harvey and Martha Erickson for their
skillful preparation of the photographs and drawings, and
C. J. Durden, who made the preliminary sorting of the silicified
Peabody Museum material.

Genus TANCREDIOPSIS
Author. Beushausen, 1895, p. 70.

Type Species. Ctenodonta contracta Salter (1859, p. 37)
[=T'ellinomya cuneata Hall, 1856, p. 8392] by subsequent des-
ignation of Cossmann, 1897, p. 94.

4 Postilla Yale Peabody Museum No. 74

Discussion. Most Ordovician nuculoid peleceypods have been
described under the generic name Ctenodonta Salter, 1852,
which has as its type the large and distinctive, but rather
uncommon Ordovician species Ctenodonta nasuta (Hall), 1847
(see Wilson, 1956, pl. 2 for illustrations of this species). In
an attempt to subdivide further the complex of species tradi-
tionally assigned to “Ctenodonta,” Beushausen proposed the
subgeneric name T'ancrediopsis for more common, smaller, early
Paleozoic nuculoids typified by the Ordovician species Cteno-
donta contracta Salter (1859) and the Silurian species Nucwa
sulcata Hisinger (1841), both of which were originally desig-
nated by Beushausen as the “types” of his new subgenus.
The first subsequent designation of one of these species as the
type of the subgenus was made by Cossmann two years after
the original description (1897, p. 94), when he chose Cteno-
donta contracta Salter as the type species. It will be shown
later that the correct name for this species is T'ancrediopsis

cuneata (Hall).

Beushausen’s name T'ancrediopsis seems to have been ignored
by all later workers on Ordovician pelecypeds, but it has gained
some usage as a generic name with workers describing Silurian
and Devonian nuculcids (Prosser and Kindle, 1913; McLearn,
1924; Reed, 1931; Northrop, 1939; Sherrard, 1960). In this
regard it should be noted that even though Beushausen origi-
nally named an Ordovician and a Silurian species as the “types”
of the subgenus, the name was proposed to facilitate the deserip-
tion of Devonian species which were the subject of his mono-
graph. While it is still too early to determine the final usefulness
of the generic name, it appears likely that many of the post-
Ordovician species to which it has been apphed cannot be con-
sidered as congeneric with the type species, “Ctenodonta con-
tracta.’ The name T'ancrediopsis will, however, probably prove
useful in the future as a generic subdivision of the heteroge-
neous assemblage of Ordovician forms now included in “Cteno-
donta.” Here again, a final determination of the value of the
name must await further study of other genera and species of
Ordovician nuculoids. In anticipation of such studies it appears

that many Ordovician nuculoid species show closer affinities to

Mar. 31, 1963 Revision of T'ancrediopsis 5

“Ctenodonta contracta,” the type of T'ancrediopsis, than to
Ctenodonta nasuta, the distinctive and uncommon type of the
genus Ctenodonta. For this reason, the transfer of many Or-
dovician species from Ctenodonta to T'ancrediopsis may prove
desirable in future revisions.

Tancrediopsis cuneata (Hall)

Figures 1-80

Tellinomya cuneata Hall, 1856, p. 392, figs. 6, 7. Hall, 1857a,
p. 183, figs. 6, 7. Hall, 1857b, p. 143, figs. 6, 7. [not] Hall,
1862, p. 38, figs. 1, 2.

Ctenodonta contracta Salter, 1859, p. 37, pl. 8, figs. 4, 5.
Logan, 1863, p. 175, figs. 160a, 160b. Wilson, 1956, p. 23,
Plee2 tiesy 1-9:

Ctenodonta (Tancrediopsis) contracta (Salter). Beushausen,
1895, p. ‘70.

[?] Tellinomya contracta? (Salter). Walcott, 1884, p. 76,
pled, figs: 15, 15a.

Revised description. Shell of small size (median height of 186
measurable specimens 8 mm), equivalved, strongly convex, thick
and massive, constricted posteriorly.” Shape variable, height
ranging from 62 to 86 per cent of length (median of 86 meas-
urable specimens 71 per cent). Surface sculpture of very fine,
widely spaced concentric ridges which are commonly divided
into rod-like pustules, especially near the outer margin (figs.
4-7, 18, 19, 24, 26, 28, 35, 37). Sculpture usually obscure or
absent, probably because of difficulty of preservation rather
than absence on original shell. The dorsal margin shows a
prominent oval lunule anterior to the umbeones and a more
elongate and obscure posterior escutcheon (figs. 65-73). Lu-
nule and escutcheon variable in size and shape. Strong, chev-
ron-shaped, taxodont dentition with approximately equal num-

2 By analogy with living nuculoids, the smaller, contracted end of T.
cuneata is considered to be posterior and the larger end to be anterior
as shown in figs. I and 2.

6 Postilla Yale Peabody Museum No. 74

bers of teeth on both sides of umbo, teeth decreasing abruptly
in size but apparently continuous in umbonal region (figs. 46-
64, 73-80). One well-preserved specimen shows several tiny
perforations along the margins of the escutcheon, probably
representing an extreme elongation of the dental sockets (fig.
71; see Sorgenfrei, 1937, and Trueman, 1952, for discussions
of similar structures in Cenozoic nuculoids). Resilifer
absent. Several specimens show a strong, external ligament
structure preserved as a silicified replica along the anterior
third of the escutcheon posterior to the umbones (figs. 65-67,
69, 70, 72, 80). Strong, subequal adductor scars deeply im-
pressed into the thick shell material, bounded cn interior side
by thickened shell material making raised ridge which is most
prominent behind the anterior scar (figs. 75-80). Two small
but deeply impressed subequal pedal muscle scars cecur just
below the hinge plate at the dorsal end of these adductor
ridges (figs. 74-80). A few well-preserved specimens also show
faint impressions just below the posterior hinge plate which
may represent cther pedal or visceral muscle scars (figs. 75,
77). Pallial line not preserved, probably very faint or absent
on original shell material. Original calcareous shell material

unknown, replaced by amorphous silica in all specimens.

Types. Lectotype of Tellinomya cuneata Hall, here des-
ignated, the specimen shown by Hall, 1856, as fig. 7 (and
fig. 6 if both figures represent the same specimen), p. 392;
whereabouts unknown. Type locality: “Pauquette’s Rapids on
the Ottawa River” [between Allumette Island, Quebee and
Ontario mainland, about three miles south of Waltham, Que-
bec, Canada (see Kay, 1942, pl. 6) ]. Stratigraphic position:
“Beds lying at the junction of the Trenton and Black River
limestones” [Rockland beds cf the Ottawa formation, Middle
Ordovician (lower Trenton stage of Twenhofel, 1954) |. Lecto-
type of Ctenodonta contracta Salter, by designation of Wil-
son, 1956, p. 28, No. 1171b in the collections of the Geological
Survey of Canada, Ottawa, Ontario, Canada. This specimen
is one of Salter’s original syntypes which was figured by him
(1859 )as pl. 8, figs. 5, 5a. Type locality: ‘‘Allumette Islands,”

Mar. 31, 1963 Revision of T'ancrediopsis 7
Quebec [probably Paquette Rapids between Allumette Island,

Quebec and Ontario mainland, about three miles south of Wal-
tham, Quebec, Canada (see Kay, 1942, pl. 6) |]. Stratigraphic

lun

anterior posterior

Figure 1. Vanerediopsis cuneata (Hall). Generalized dorsal view of artic-
ulated valves showing lunule (lun), ligament (lig), escutcheon (es) and
escutcheonal perforations (ep).

apm
ppm

aam
pam

anterior posterior

. — Spue™
sepasiaia oo

Figure 2. Tancrediopsis cuneata (Hall). Generalized interior view of
right valve showing anterior adductor muscle scar (aam), anterior pedal
muscle scar (apm), posterior pedal muscle scar (ppm), posterior adductor
muscle scar (pam), and additionai possible pedal or visceral muscle scars
along posterior dorsal margin (pm?).

position: ‘*Allumette limestenes” [probably Rockland beds of
the Ottawa formation, Middle Ordovician (lowest Trenton
stage of T'wenhofel, 195+) ].

8 Postilla Yale Peabody Museum No. 74

The location of Hall’s original figured specimen is unknown,
for it is not listed in the type catalogues of either the Ameri-
can Museum of Natural History or the New York State Mu-
seum (Whitfield and Hovey, 1898-1901; Clarke and Ruede-
mann, 1908), the two institutions which contain most of Hall’s
original material. The specimen may be as yet unrecognized
among the non-type material at these or other institutions.
Hall’s original figure leaves little room for doubt, however, as
to the identity of the species in question, and the designation
of a neotype therefore seems unnecessary.

Material. This revised description is based on 189 silicified
valves. Fifteen of these are Salter’s original types of Cteno-
donta contracta from the collections of the Geological Survey
of Canada, Ottawa, Ontario, Canada (catalogue No. 1171).
The remaining 174 specimens are from the collections of the
Peabody Museum, Yale University, New Haven, Connecticut,
U.S. A. All of Salter’s specimens and almost half of the Yale
material (75 specimens) were collected at Paquette Rapids
(between Allumette Island, Quebec and Ontario mainland,
about three miles south of Waltham, Quebec, Canada; see Kay,
1942, pl. 6) which is the original type locality of both T'el-
linomya cuneata Hall and Ctenodonta contracta Salter. The
remaining Yale specimens (99) were collected from Middle
Ordovician limestones of approximately the same age exposed
at Pointe Bleue on the shores of Lake St. John, about five
miles north of Roberval, Quebec, Canada (see Dresser, 1916,
map 184A). Both Yale collections were made in 1903 by C. E.
Beecher and P. EK. Raymond. The original specimens studied
by Salter were collected by W. E. Logan in 1845. The distribu-
tion of specimens of T'ancrediopsis cuneata at these institu-
tions and localities is shown in more detail in Table 1.

The material shows considerable variation in the quality of
the silicified preservation. In some specimens the whole valve is
preserved, but many valves were incompletely replaced by silica
and do not show the entire outline. The fragile posterior ex-
tremity is commonly missing, but the heavy hinge plate and
dentition are almost always preserved. The specimens from

Mar. 31, 1963 Revision of T'ancredio psis 9

TABLE 1

Distribution of specimens of Tancrediopsis cuneata (Hall) used in this
study. For consistency, each valve of articulated individuals is counted as
one “specimen.”

Locality
and Right Left Articulated Total
Source valves valves valves specimens

Paquette Rapids

Yale Peabody Museum... 44 29 2 75
Geological Survey
OF ComeCeoocussocac 6 7 2 15
Pointe Bleue, Lake St. John
(All Yale Peabody
Nit Se um) se cdegaers cio ek- 19 20 60 99
ANOUENIS S pape oie a Screen epee 69 56 64 189

Lake St. John are generally more coarsely silicified and show
fewer morphologic details than do those from Paquette Rapids.

Occurrence. The species is known with certainty only from
the type locality and the Lake St. John locality mentioned
above, both of which probably represent horizons in the mid-
dle part of the Middle Ordovician (lowest Trenton stage of
the American standard, approximately lower Caradoc of the
uropean standard, see T'wenhofel, 1954). Several additional
Ontario and Quebec occurrences are listed by Wilson (1956,
p. 28), and the species may be represented in the Ordovician
of Nevada (Walcott, 1884). Restudy of other important
Ordovician pelecypod faunas may prove the species to be more
abundant and widespread than is apparent from the evidence
now available. In most such faunas nuculoid forms are not
silicified, but are preserved as internal or composite molds (see
McAlester, 1962). For this reason, an artifical internal mold
of a well-preserved, silicified specimen of 7’. cuneata has been
figured here to facilitate comparison with other faunas (fig.

A'7).

10 Postilla Yale Peabcdy Museum No. 74

Discussion. There has been considerable confusion in the
identification of Salter’s species “Ctenodonta contracta” and
other closely related species from the Paquette Rapids locality.
The Yale collections from this locality contain about 700 sili-
cified nuculoid specimens, and an analysis of these specimens
has revealed that at least seven species of nuculoids occur in
appreciable numbers at Paquette Rapids. Several additional
nuculoid species probably also occur in the fauna but are quite
rare and are represented by only a few specimens from the
Yale collections. Five of the seven common species are distinc-
tive and cause little confusion in identification. Wilson (1956,
pl. 2) illustrates four of these distinctive species, which are
identified by her as: Ctenodonta astartaeformis Salter, Cteno-
donta levata (Hall), Ctenodonta nasuta Hall, and Ctenodonta
logant Salter. A fifth common species, a small Palaeoneilo-like
form, is not mentioned by Wilson and may be as yet un-
described.

It is the final two common nuculoid species in the Paquette
Rapids fauna which are easily confused. Both are medium-sized
(for nuculoids), thick-shelled forms with contracted posterior
extremities, strong adductor impressions, and similar patterns
of dentition. Analysis of the large Yale collections shows that
the two forms do, however, show consistent and distinct dif-
ferences in shape, which are most cbvyious from comparing the
shell exteriors. To facilitate comparison the two species will
be referred to here as “Form A” and “Form B.” Form A
has more central umbones, a more elongate and_ gently-
sloping posterior constriction, and a differently shaped an-
tericr-ventral and anterior margin. Internally, the differences
are less distinctive, but the more central umbones, less abrupt
posterior constriction, and longer posterior dentition of Form
A can usually be recognized. Form B also seems to have lacked
the very fine, pustulose, concentric sculpture seen on well-pre-
served specimens of Form A. Form B also appears to have had
weaker and somewhat differently oriented pedal muscle scars.
In Form A the chevron-shaped teeth point toward the umbo,
whereas they tend to point away from the umbo in Form B.
These differences in shape and sculpture are shown in fig. 3.

Mar. 31, 1965 Revision of T'ancrediopsis 11

There are no morphological intermediates between these two
common forms in the Paquette Rapids fauna, and they cer-
tainly represent two closely related sympatric nuculoid species.
Among approximately 700 identifiable nuculoid specimens from
the locality in the Yale collections, about 250 (86 per cent)
are form B, 75 (or about 11 per cent) are Form A, and the
bulk of the remainder (about 375 specimens or 53 per cent) rep-
resent the five additional species mentioned above. The lectotype
of Hall ’s species T'ellinomya cuneata is readily recognizable

T. cuneata T. ‘‘abrupta”’
(‘Form A’’) (‘Form B")

INTERIOR
(right valves)

EXTERIOR
(left valves)

Figure 3. Internal and external views showing morphologic differences be-
tween the closely related sympatric species Tancrediopsis cuneata (Hall)
and Tancrediopsis “abrupta”’ (Billings).

from the original figure as belonging to Form A (sub-central
umbones, elongate posterior, etc.) as are also the lectotype
and other original specimens of Ctenodonta contracta Salter.
The lectotypes of both species are from Paquette Rapids, and
there is little doubt that the two names are synonyms.

Hall’s name “T'ellinomya cuneata” was not formally pro-
posed as a new species, but was merely first listed in explana-
tion of figures of “T'ellinomya” [—=Ctenodonta]| in a discus-
sion of the genus (1856) which was later reprinted in two
forms (1857a, 1857b). Characters of the species are, however,
briefly mentioned in Hall’s text (p. 392 in the original report).

The figures and discussion of the species in Hall’s report cer-

12 Postilla Yale Peabody Museum No. 74

tainly constitute a valid description or “indication” of a new
species as prescribed in the rules of nomenclature (see Stoll,
1961, p. 15), and Hall’s name, which has three-years priority
over Ctenodonta contracta Salter, is therefore accepted here
as the correct name for the species. This strict usage of prior-
ity may violate the new “nomen oblitum” provision of the
nomenclatural cede which provides that ‘ta name that has re-
mained unused as a senior synonym in the primary zoological
literature for more than fifty years is to be considered a for-
gotten name (nomen oblitum). . . [and] is not to be used un-
less the Commission so directs” (Stoll, 1961, p. 23). However,
the application of the rule is ambiguous in this case because
Tellinomya cuneata has appeared in what is presumably the
“primary zoological literature” as an incorrectly suppressed
senior synonym of Ctenodonta contracta within the past fifty
years (Bassler, 1915, p. 302). In addition, the prescribed pro-
cedure for applying the rule is extremely cumbersome and in
my opinion will do more to create nomenclatural instability
than to correct it because every “nomen oblitum’”? must be
laboriously referred to the Commission for action. For these
reasons I prefer a strict interpretation of the Law of Priority
in this case (for additional objections and comment on the
“nomen oblitum” provision see the Bulletin of Zoological No-
menclature, Volume 19, Part 6, 28 December, 1962).

The name of the second common species (‘Form B’’) is not
yet certain, but it appears that the lectotype of Ctenodonta
abrupta Billings (1862; see also Wilson, 1956) is a represent-
ative of “Form B,” and this may be the correct name for the
species. These two closely related species (T'ancrediopsis cu-
neata and “Ctenodonta abrupta”’) are certainly congeneric
and thus C. abrupta would become T'ancrediopsis “abrupta”

(Billings).

In addition to these two common species of T'ancrediopsis,
a few other specimens from the Paquette Rapids fauna may
represent closely related but very rare species. Several such
specimens in the Yale collections do not appear to fall within
the range cf shape variation of either 7. cuneata or T. “ab-
rupta,” but at present these specimens are too rare either to

Mar. 31, 1963 Revision of T'ancrediopsis 13

warrant specific names or to cause confusion in the identifica-
tion of 7’. cuneata. The original figured specimen of Cteno-
donta gibberula Salter (1859, pl. 8, fig. 6) may represent one
such species but, regrettably, the specimen appears to have
been lost (see Wilson, 1956, p. 24). Pending the discovery of
the original specimen or similar additional material, it does
not seem prudent to recognize Salter’s name. The two names
C. abrupta Billings and C. gibberula Salter appear to be the
only names proposed for Paquette Rapids specimens which are
closely related to JT’. cuneata.

In comparison to the Paquette Rapids fauna, nuculoids are
somewhat less common and more poorly preserved in the silici-
fied fauna from Lake St. John, but the fauna does contain
many articulated specimens which are rare at Paquette Rapids
(see Table 1). The nuculoid species at Lake St. John all ap-
pear to be indistinguishable from those at Paquette Rapids,
although the relative abundances differ at the two localities.
At Lake St. John, 7T'. cuneata is over three times as abundant

as T’. “abrupta” (99 vs. 30 specimens), whereas this situation

is reversed at Paquette Rapids where 7’. “abrupta” strongly
dominates (approximately 250 specimens vs. 75 specimens of
T’. cuneata).

LITERATURE CITED

Beushausen, Ludwig, 1895. Die Lamellibranchiaten des rheinischen Devon
mit Ausschluss der Aviculiden: Kgl. Preussischen Geol. Landesanstalt
Abh., Neue Folge, no. 17, 514 p., 38 pls.

Billings, Elkanah, 1862. New species of Lower Silurian fossils [part 2]:
Montreal, Geol. Survey Canada, p. 25-56 [reprinted in 1865 as part of
“Palaeozoic Fossils,” v. 1].

Clarke, J. M., and Ruedemann, Rudolph, 1903. Catalogue of type specimens
of Paleozoic fossils in New York State Museum: New York State Mus.
Bull. 65, 847 p.

Cossmann, Maurice, 1897. Revue critique de paléozoologie, premiére année
Nos. 1-4): Paris, Société d’Editions Scientifiques, 186 p.

Cox, L. R., 1959. The geological history of the Protobranchia and the dual
origin of taxodont Lamellibranchia: Malacological Soc. London Proc.,
vy. 33, p. 200-209.

Dresser, J. A., 1916. Part of the district of Lake St. John, Quebec: Canada
Geol. Survey Mem. 92, geol. ser. no. 74, 88 p., 5 pls.

Hall, James, 1856. On the genus Tellinomya and allied genera; Canadian
Naturalist and Geologist, v. 1, p. 390-395.

14 Postilla Yale Peabody Museum No. 74

———, 1857a. On the genus Tellinomya and allied genera: Regents
of the Univ. of the State of New York, State Cabinet of Nat. History,
10th Ann. Rept., App. C, p. 181-186.

, 1857b. On the genus Tellinomya and allied genera, in Descrip-
tions of new species of Palaeozoic fossils, etc., extracted from 10th
Ann. Rept. Regents of the Univ. of the State of New York: p. 141-146.

—, 1862. Physical geography and general geology; Remarks upon
the condition of the fossils, ete., in Hall, James, and Whitney, J. D.,
Rept. Geol. Survey Wisconsin, v. 1: p. 1-72 (chap. 1), 425-448 (chap. 9).

Hisinger, Wilhelm, 1841. Lethaea Svecica sue petrificata Sveciae, iconibus et
characteribus illustrata [2nd supplement, part 2]: Holmiae, 6 p., pls.
40-42. eee

Kay, G. M., 1942. Ottawa-Bonnechere graben and Lake Ontario homo-
cline: Geol. Soc. America Bull, v. 53, p. 585-646.

Knight, J. B., 1941. Paleozoic gastropod genotypes: Geol. Soc. America
Spec. Paper 32, 510 p., 96 pls.

Logan, W. E., and others, 1863. Geology of Canada; Geological Survey of
Canada, Report of progress from its commencement to 1863, ete.:
Montreal, Dawson Brothers, 983 p.

McAlester, A. L., 1962. Mode of preservation in early Paleozoic pelecy-
pods and its morphologic and ecologic significance: Jour. Paleontology,
vy. 36, p. 69-73.

McLearn, F. H., 1924. Paleontology of the Silurian rocks of Arisaig, Nova
Scotia: Canada Geol. Survey Mem. 137, geol. ser. no. 118, 180 p., 30
pls.

Northrop, S. A., 1939. Paleontology and stratigraphy of the Silurian rocks
of the Port Daniel-Black Cape region, Gaspé: Geol. Soc. America
Spec. Paper 21, 302 p., 28 pls.

Prosser, C. S., and Kindle, E. M., 1913. Pelecypoda, in Systematic pale-
ontology of the Middle Devonian deposits of Maryland: Maryland
Geol. Survey Middle and Upper Devonian, p. 214-279, 14 pls. [in
separate volume].

Reed, F. R. C., 1931. Some new lamellibranchs from the Silurian of the
Ludlow district: Annals and Mag. Nat. History, ser. 10, v. 8, p. 289-
304.

Salter, J. W., 1852. Note on the fossils above mentioned, from the Ottawa
River: British Assoc. Ady. Sci. Rept., 21st Mtg., 1851, Notices and
Abs., ete., p. 63-65.

, 1859. Fossils from the base of the Trenton group: Geol
Survey Canada, Figs. and Descriptions of Canadian Organic Re-
mains, decade 1, 47 p., 10 pls.

Sherrard, Kathleen, 1960. Some Silurian lamellibranchs from New South
Wales: Linnean Soc. New South Wales Proc., v. 84, p. 356-372.

Sorgenfrei, Theodor, 1937. Some remarks on the hinge of nuculids and
ledids: Vidensk. Medd. Dansk naturh. Foren. K@benhavn, vy. 100, p.
369-375.

Stoll, N. R., chairman, 1961. International code of zoological nomencla-
ture adopted by the XV International Congress of Zoology: London,
Internat. Trust for Zool. Nomenclature, 176 p.

Trueman, E. R., 1952. Observations on the ligament of Nucula: Mala-
cological Soc. London Proc., v. 29, p. 201-205.

Mar. 31, 1963 Revision of T'ancrediopsis 15

Twenhofel, W. H., chairman, 1954. Correlation of the Ordovician forma-
tions of North America: Geol. Soc. America Bull., v. 65, p. 247-298.

Walcott, C. D., 1884. Paleontology of the Eureka district [Nevada]: U.S.
Geol. Survey Mon. 8, 298 p., 24 pls.

Whitfield, R. P., and Hovey, E. O., 1898-1901. Catalogue of the types and
figured specimens in the paleontological collection of the geological
department, American Museum of Natural History: Am. Mus. Nat.
History Bull., v. 11, 500 p.

Wilson, A. E., 1956. Pelecypoda of the Ottawa formation of the Ottawa-
St. Lawrence Lowland: Geol. Survey Canada Bull. 28, 102 p., 9 pls.

Postilla Yale Peabody Museum No. 74

Figures 4-21. Tancrediopsis cuneata (Hall). A series of exterior views of
silicified right valves showing variation in shape and sculpture. All figures
are twice natural size. Precise locality information for the ‘Paquette Ra-
pids” and “Lake St. John” localities is given in the text. YPM=Yale
University Peabody Museum collections, New Haven, Connecticut, U.S.A.
GSC = Geological Survey of Canada collections, Ottawa, Ontario, Canada.

Figure 4. YPM 22966, Lake St. John. Figure 5. YPM 22967, Lake St.
John. Figure 6. YPM 22968, Lake St. John. Figure 7. YPM 22969,
Lake St. John. Figure 8. YPM 22970, Lake St. John. Figure 9. YPM
22971, Paquette Rapids. The specimen lacks the anterior and_pos-
terior extremities. See also fig. 48. Figure 10. YPM 22972, Paquette
Rapids. The specimen lacks the posterior extremity. Figure 11. YPM
22973, Lake St. John. Figure 12. YPM 22974, Lake St. John. Figure
13. YPM 22975, Paquette Rapids. The specimen lacks the anterior
extremity. See also fig. 50. Figure 14. YPM 22976, Paquette Rapids.
The specimen lacks the anterior and posterior extremities. Figure 15.
YPM 22977, Paquette Rapids. See also figs. 52, 68. Figure 16. YPM
22978, Lake St. John. Figure 17. GSC 1171c, Paquette Rapids. One of
Salter’s original specimens of Ctenodonta contracta, figured by Wil-
son, 1956, as figs. 7 and 8 of pl. 2. See also fig. 70. Figure 18. YPM
22979, Paquette Rapids. The anterior part of the specimen is missing.
Figure 19. GSC 1171k, Paquette Rapids. One of Salter’s original
specimens of Ctenodonta contracta, figured by Wilson, 1956, as fig.
9 of pl. 2. The specimen lacks the anterior extremity. Figure 20.
GSC 117le, Paquette Rapids. One of Salter’s original specimens of
Ctenodonta contracta. See also fig. 66. Figure 21. YPM 22980,
Paquette Rapids. See also figs. 47, 55, 77, 79.

Mar. 31, 19638 Revision of T'ancrediopsis il

Figures 22-47. Tancrediopsis cuneata (Hall). Figures 22 through 42
are a series of exterior views of silicified right valves showing variation
in shape and sculpture. Figures 43 through 45 are dorsal views of three
articulated silicified specimens (anterior end to left). Figure 46 is an
interior view of the largest known specimen, a silicified left valve. Figure
47 is a latex internal mold of a silicified right valve showing the appear-
ance of the species as normally preserved in non-silicified faunas. All
figures are twice natural size. Precise locality information for the
“Paquette Rapids” and “Lake St. John” localities is given in the text.
YPM=/Yale University Peabody Museum collections, New Haven, Con-
necticut, U.S.A. GSC = Geological Survey of Canada collections, Ottawa,
Ontario, Canada.

Figure 22. YPM 22981, Lake St. John. Figure 23. YPM 22982, Lake
St. John. Figure 24. YPM 22983, Lake St. John. Figure 25. YPM
22984, Lake St. John. Figure 26. YPM 22985, Lake St. John. Figure
27. YPM 22986, Lake St. John. Figure 28. YPM 22987, Lake St. John.
Figure 29. YPM 22988, Lake St. John. Figure 30. YPM 22989, Lake
St. John. Figure 31. YPM 22990, Lake St. John. Figure 32. YPM
22991, Paquette Rapids. The specimen lacks the anterior extremity.
See also fig. 58. Figure 33. YPM 22992, Lake St. John. Figure 34.
GSC 11711, Paquette Rapids. One of Salter’s original specimens of
Ctenodonta contracta. See also fig. 43. Figure 35. GSC 1171j, Paquette
Rapids. Figure 36. YPM 22993, Lake St. John. See also fig. 44.
Figure 37. YPM 22994, Lake St. John. Figure 38. YPM 22995, Lake
St. John. See also fig. 45. Figure 39. Lectotype of Ctenodonta con-
tracta Salter, GSC 1171b, Paquette Rapids, figured by Salter, 1859,
as figs. 5 and 5a of pl. 8. The specimen lacks the posterior extremity.
See also figs. 61, 67, 75, 80. Figure 40. GSC 1171m, Paquette Rapids.
One of Salter’s original specimens of Ctenodonta contracia. The
specimen lacks the anterior extremity. See also figs. 60, 73, 76. Figure
41. GSC 1171i, Paquette Rapids. One of Salter’s original specimens of
Ctenodonta contracta. See also fig. 69. Figure 42. GSC 1171d,
Paquette Rapids. One of Salter’s original specimens of Ctenodonta
contracta, Figure 43. GSC 1171L, Paquette Rapids. One of Salter’s
original specimens of Ctenodonta contracta. See also fig. 34. Figure
44. YPM 22993, Lake St. John. See also fig. 36. Figure 45. YPM
22995, Lake St. John. See also fig. 38. Figure 46. GSC 1171a, Paquette
Rapids. One of Salter’s original specimens of Ctenodonta contracta,
Figure 47. Latex cast of YPM 22980, Paquette Rapids. See also figs.
le Gy (U5 Ue

18 Postilla Yale Peabcdy Museum No. 74

Figures 48-64. Tancrediopsis cuneata (Hall). A series of internal views of
silicified valves showing dentition and adductor musculature. Figures 48
through 56 are right valves; figures 57 through 64 are left valves. All
figures are twice natural size. Precise locality information for the
“Paquette Rapids” locality is given in the text. YPM=Yale University
Peabody Museum collections, New Haven, Connecticut, U.S.A. GSC=
Geological Survey of Canada collections, Ottawa, Ontario, Canada.

Figure 48. YPM 22971, Paquette Rapids. See also fig. 9. Figure 49.
YPM 22996, Paquette Rapids. Figure 50. YPM 22975, Paquette Rap-
ids. See also fig. 13. Figure 51. YPM 22997, Paquette Rapids. Figure
52. YPM 22977, Paquette Rapids. See also figs. 15, 68. Figure 53.
YPM 22998, Paquette Rapids. Figure 54. GSC 1171g, Paquette Rap-
ids. One of Salter’s original specimens of Ctenodonta contracta. See
also fig. 72. Figure 55. YPM 22980, Paquette Rapids. See also figs.
21, 47, 77, 79. Figure 56. YPM 22999, Paquette Rapids. See also fig.
74. Figure 57. YPM 23000, Paquette Rapids. Figure 58. YPM 22991,
Paquette Rapids. See also fig. 32. Figure 59. YPM 23001, Paquette
Rapids. See also fig. 78. Figure 60. GSC 1171m, Paquette Rapids.
One of Salter’s original specimens of Ctenodonta contracta. See also
figs. 40, 73, 76. Figure 61. Lectotype of Ctenodonta contracta Salter,
GSC 1171b, Paquette Rapids, figured by Salter, 1859, as figs. 5 and
5a of pl. 8 See also figs. 39, 67, 75, 80. Figure 62. YPM 23002,
Paquette Rapids. Figure 63. YPM 23003, Paquette Rapids. Figure
64. YPM 23004, Paquette Rapids. See also fig. 71.

Mar. 31, 1963 Revision of T'ancrediopsis UM,

Figures 65-80. Tancrediopsis cuneata (Hall). A series of enlarged views of silici-
fied valves showing details of ligament, dentition, and musculature. All figures are
three times natural size except Figure 65 (twice natural size) and Figure 71 (six
times natural size). Precise locality information for the “Paquette Rapids” locality
is given in the text. YPM=Yale University Peabody Museum collections, New
Haven, Connecticut, U.S.A. GSC=Geological Survey of Canada collections, Ot-
tawa, Ontario, Canada.

Figure 65. GSC 1171f, Paquette Rapids. One of Salter’s original figured speci-
mens of Cfenodonta contracta, illustrated by Salter, 1859, as figs. 4 and 4a of
pl. 8. Dorsal view of articulated valves (anterior end to left) showing lunule,
escutcheon, and silicified replica of ligament. Figure 66. GSC 117le, Paquette
Rapids. One of Salter’s original specimens of Ctenodonta contracta. Dorsal
view of right valve showing lunule, escutcheon, and silicified replica of liga-
ment. See also fig. 20. Figure 67. Lectotype of Ctenodonta contracta Salter,
GSC 1171b, Paquette Rapids, figured by Salter, 1859, as figs. 5 and 5a of pl. 8.
Oblique dorsal view of left valve showing lunule, escutcheon, and _ silicified
replica of ligament. See also figs. 39, 61, 75, 80. Figure 68. YPM 22977, Paquette
Rapids. Oblique dorsal view of right valve showing lunule. See also figs. 15,
52. Figure 69. GSC 1171i, Paquette Rapids. One of Salter’s original specimens
of Ctenodonta contracta. Oblique dorsal view of left valve showing escutcheon
and silicified replica of ligament. See also fig. 41. Figure 70. GSC 1171c, Paquette
Rapids. One of Salter’s original specimens of Ctenodonta contracta, figured by
Wilson, 1956, as figs. 7 and 8 of pl. 2. Oblique dorsal view of right valve interior
showing lunule, escutcheon, and silicified replica of ligament. See also fig. 17.
Figure 71. YPM 23004, Paquette Rapids. Enlarged dorsal view of left valve
showing lunule, escutcheon, and tiny perforations along posterior margin of
escutcheon. See also fig. 64. Figure 72. GSC 1171g, Paquette Rapids. One of
Salter’s original specimens of Ctenodonta contracta. Oblique dorsal view of
right valve showing lunule, escutcheon, and silicified replica of ligament. See
also fig. 54. Figure 73. GSC 1171m, Paquette Rapids. One of Salter’s original
specimens of Ctenodonta contracta. Oblique dorsal view of left valve showing
lunule, escutcheon, and dentition. See also figs. 40, 60, 76. Figure 74. YPM 22999,
Paquette Rapids. Oblique ventral view of interior hinge region of right valve
showing anterior and posterior pedal muscle scars and dentition. See also fig. 56.
Figure 75. Lectotype of Ctenodonta contracta Salter, GSC 1171b, Paquette
Rapids, figured by Salter, 1859, as figs. 5 and 5a of pl. 8. Ventral view of left
valve interior showing dentition, adductor muscle scars, strong rounded anterior
and posterior pedal muscle scars, and faint additional pedal? muscle scars
below posterior dentition. See also figs. 39, 61, 67, 80. Figure 76. GSC 1171m,
Paquette Rapids. One of Salter’s original specimens of Ctenodonta contracta.
Oblique ventral view of left valve interior showing dentition and posterior ad-
ductor and pedal muscle scars. See also figs. 40, 60, 73. Figure 77. YPM 22980,
Paquette Rapids. Ventral view of right valve interior showing adductor muscle
scars, strong rounded anterior and posterior pedal muscle scars, and faint addi-
tional pedal? muscle scars below posterior dentition. See also figs. 21, 47, 55, 79.
Figure 78. YPM 23001, Paquette Rapids. Oblique ventral view of left valve
interior showing dentition, anterior adductor muscle scar, anterior and posterior
pedal muscle scars. See also fig. 59. Figure 79. YPM 22980, Paquette Rapids.
Interior view of right valve showing dentition, adductor muscle scars, and pedal
muscle scars. See also figs. 21, 47, 55, 77. Figure 80. Lectotype of Ctenodonta
contracta Salter, GSC 1171b, Paquette Rapids, figured by Salter, 1859, as figs.
5 and 5a of pl. 8. Interior view of left valve showing dentition, adductor muscle
sears, pedal muscle sears, and silicified replica of ligament. See also figs. 39, 61,
67, 75.

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