IGS.

CARDED

ON THE NORTH AMERICAN SPECIES OF THE GENUS
ATAX (FABR.) BRUZ.

ROBERT H. WOLCOTT.

GENERAL CONSIDERATIONS.

One who opens many of our fresh-water mussels, cannot fail
to notice, in part of them at least, dark spots upon the mantle or
gills, which a moment’s observation will show are living, moving
organisms. A lens will reveal the fact that they have four pairs
of six-jointed legs and a pair of five-jointed palpi, but no
antenne-like structures, that the head, thorax and abdomen are
fused into one mass with no trace of segmentation, and that
the relatively long legs are clothed with spines and hairs which
assist in swimming. Two small blackish or brownish eyes
may be detected near the anterior margin. These characters
point to the taxonomic position of these creatures in the order
Acarina or Mites and in the family Hydrachnide or Water—
Mites, while their presence in the mussel suggests their mem-
bership in the genus A¢ax, the members of which are mussel—
parasites, during at least a part of their existence. Rarely
representatives of other non-parasitic genera may be found
within these shells, but their occurrence there is purely acci-
dental; on the other hand few species of this genus are found
except in mussels. However, the genus is not confined to the
Unionide, a single species having been found in the mantle—
cavity of a South American gasteropod, Ampullaria, related
to our genus Campeloma, and the author having detected
another previously described species in a species of Spheriui,
one of the Cyrenide.

In scanning the literature on the subject we discover but
scattered references to Hydrachnide, under the generic term
Acarus, previous to 1781, when O. F. Miiller described 49
species from Denmark, establishing for them the new genus

13

194 : ROBERT H. WALCOTT:

Hydrachna. In 1793, J. C. Fabricius included all these under
Trombidium, but in 1805 he established the genus Ataa which
was equivalent to Hydrachna of Miiller. Previously, in 1796,
P. A. Latreille had erected the genera Zémnochares and
Liylais, but these were by Fabricius included under Ataw. In
1834, Antoine Dugés restricted the name Hydrachna to a few
species which are still so classified, re-established the genera
Limnochares and Hylais, and separated from Ataw Fabricius,
which included the greater number of the species, the additional
genera Diplodontus and Arrenurus. In 1837 the genus of
Fabricius was still more sharply limited by C. L. Koch, who
separated several new genera; but only in 1854 and by
Ragnar Bruzelius was the genus Afax reduced to the limits
which were for forty years accepted by all students of the
group as its natural bounds and are by many still so regarded.
In 1894 Richard Piersig, on grounds considered insufficient by
Koenike, separated from Ataw the genus Cochleophorus, and
in the past year, 1897, he has proposed another new genus,
Encentridophorus, to include a species described by Koenike
from East Africa, and the genus Vajadicola to include one of
our American species, also described by Koenike. The char-
acters which separate Cochleophorus from Atawz, as thus
limited, are sufficient, it seems to the author, to render the
former a valid genus; certainly the two designate clearly de-
fined groups of species and all described forms fall naturally
into one or the other of these groups. In accordance with this
view the species included under Cochleophorus are excluded
from this paper. In regard to Wajadicola, however, while it
possesses certain characters which differ from those of other
species of parasitic mites, the writer has been unable to agree
with Piersig in thinking these differences such as to entitle it
to more than sub-generic rank.

As in the above manner limited, the characters of the genus
Atax are thus defined by Piersig in his ‘‘Deutschlands Hy-
drachniden’’ (97):

Body soft, with but a slight tendency to the formation of
chitinous thickenings over the surface, round or oval; on the

NORTH AMERICAN SPECIES OF THE GENUS ATAX La

anterior margin no concavity; the posterior margin evenly
rounded or with a shallow median concavity. The first pair
of legs distinguished by an unusual thickness and in the non—
parasitic species provided with long, stout, movable, sword-
shaped spines, inserted into prominently projecting papille.
Second pair usually exceeding the third in length. The pro-
portion between the length of the body and legs quite variable,
but generally the legs of the parasitic species shorter than these
of the non-parasitic. The maxillary shield is not fused with
the neighboring epimera. In ventral view it resembles in
shape a broad chalice. The palpi are long; in the parasitic
forms they equal or exceed in thickness the first pair of legs.
The next to the last segment possesses on its ventral side three
papille varying in size in different species; of these the one
at the outer end ends in a chitinous spur, while the two others
placed somewhat farther posteriorly are each crowned with a
little hair. The fifth palpal segment is short and provided with
chitinous claws. Among the epimera those of the fourth pair
are distinguished by their size and more or less rectangular
form. Third epimeron imperfectly separated from the fourth.
Genital area at the extreme end of the body. The chitinous
plates surrounding the genital cleft from either side, bear to-
gether 10, 12, or numerous, acetabula. In the females charac-
teristic sword-like spines appear in the vicinity of the genital
opening, which are employed in oviposition.

This diagnosis is not strictly applicable to all of our species,
even excluding Atax (Wajadicola) ingens (Koenike), since both
A. abnormipes mihi and A. indistinctus mihi are deeply emargi-
nate posteriorly, A. pectinatus mihi is a non-parasitic form yet
lacks the movable spines on the first pair of legs, and the
genital area is not in all forms at the extreme end of the body,
though usually approaching that position.

The sub-genus Vajadicola difters in the following respects.
The fore legs are not thickened, and all are short, with few
short spines and simple claws. The genital area is not at the
end of the body but immediately behind the last epimera and
as Koenike’s figures show, bears a certain resemblance to

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196 ROBERT H. WOLCOTT:

that of Cochleophorus. It is, however, much broadened trans-
versely, and each genital plate is triangular in outline. There
are no spines about the genital opening of the female and the
lack of these is correllated with the method of oviposition, A.
(LV.) ingens Koenike depositing its eggs in masses between the
gills and not in them.

Of the genus Az¢ax as thus defined there have been hereto-
fore described 22 valid species, distributed geographically as
follows:

From Europe, 8: A. aculeatus Koenike (Germany), A. Bonze
Claparéde (Germany, Sweden, Switzerland, France, Russia)
A. crassipes (Miiller) (Finland, Russia, Switzerland, Denmark,
Germany, Italy, France), A. figuralis Koch (Germany), A.
mtermedius Koenike (Belgium, Germany, Russia), A. limosus
(Koch) Berlese (Italy, Germany), A. tricuspis Koenike (Ger-
many) A. ypsilophorus (Bonz) (Sweden, Germany, Switzer-
land, France).

From Asia, 3: A. crassipes (Miiller) is recorded from Pales-
tine, and A. Schmacheri Koenike was described from Shanghai,
China, while Daday has recently published one from Ceylon,
A. singalensis, while his A. nodosus belongs to Cochleophorus.

From Africa, 1: A. lynceus Koenike from East Africa.

From Brazil, 6: A. Ampullarie Koenike, <A. jissipes
Koenike, A. JSheringi Koenike, A. perforatus Koenike, A.
procurvipes Koenike, A. rugosus Koenike, all from the
province of Rio Grande do Sul.

From Guatemala, 3: A. alticola Stoll, A. dentipalpis Stoll
and A. septem-maculatus Stoll.

A. alzatei Alf. Dugés, described from Mexico, is a species
of Curvipes.

From North America, A. ypstlophorus (Bonz) has several
times been recorded and Koenike adds to it from Canada A.
Fossulatus Koenike and A. (lV.) ingens (Koenike).

Our own literature is not entirely wanting in references to
this genus, but the work done by Americans has for the most
part been practically worthless, while efforts made to secure
the original specimens have resulted in failure, as would be ex-

NORTH AMERICAN SPECIES OF THE GENUS ATAX 197

pected from the number of years that have elapsed, the nature
of the specimens, and the crudity of methods of preservation
in vogue at the time they were described.

Thos. Say, in 1821, described Hydrachna triangularis from
Unio cariosus Say; in so doing he may have re-described Ataw
ypsilophorus (Bonz) as other authors have inferred, although
from his description it is impossible to say which species he
had under observation. In 1836, James D. Dana and James
Whelpley, in Silliman’s Journal, described two forms, //y-
drachna formosa from ‘* Anodonta cataracta”’ (A. fluviatilis
Dillw.) and ‘* Unio purpurata’’ (an incorrect identification as
U. purpuratus Lam. is Southern in its habitat); and Hydrachna
pyriformis from Margaritana undulata Say. The former is
another synonym of A. ypsilophorus (Bonz), the latter a dis-
tinct species, but the characters given are not sufficient for
exact determination. Its form and the character of the claws
which are described as simple, seem to show that it is a female
of either A. abnormipes mihi or A. indistinctus mihi, but of
which it is impossible to tell. In 1842, 8. S. Haldeman
described under the ‘‘Genus? Unzonicola’’ nine species:
oviformis, lactea, personata, humerosa, symmetrica, proxima,
lugubris, unicolor and reticulata—with very short descrip-
tions, based mostly on color. Two of the nine are identi-
cal with A. ypstlophorus (Bonz), while the other seven are
probably the same, as Koenike (95b) suggests. Joseph
Leidy, in 1883, noted the presence of the same European
form in Anodonta fluviatilis Dillw. from New Jersey, and
mentions the occurrence in Unio complanatus Sol. of a second
species, ‘‘probably’’, he says, ‘‘.A. Bonzz”’, also a previously
described European form. In 1891, F. Koenike of Bremen,
Germany, published a preliminary account (91c) of some
material received from Dr. Tyrrell in Ottawa, Canada, con-
firming Leidy’s observation as to the occurrence of A. yps¢l-
ophorus (Bonz) in North America, but, and it seems rightly,
throwing doubt on his identification of A. Bonz? Claparéde. In
1895, a fuller paper (95b) on the same material by the same
author appeared and in it he enumerated the species previously

EEE

198 ROBERT H. WOLCOTT:

mentioned—A. ypsilophorus (Bonz), A. fossulatus Koenike
and A. (lV.)ingens (Koenike).

The collection of material upon which the present paper is
based was begun in 1893 and has been carried on, as oppor-
tunity offered, ever since. During the five years the following
collections of Unionide have been made and examined for
mites:

August, 1893, at Lake Saint Clair, Mich., 257 specimens of
Onio gracilis Barnes, U. luteolus Lam., U. nasutus Say, U.
dlatus Say, WU. ventricosus Barnes, U. gibbosus Barnes, U.
rectus Lam., U. coccineus Hild., U. undulatus Barnes, U.
occidens Lea, Margaritana rugosa Barnes, MM. deltoides Lea
and Anodonta ovata Lea.

October, 1893, at Lansing, Mich., from the Cedar River,
about a score of mussels, belonging to several species, the
record of which is, unfortunately, lost.

July and August, 1894, at Charlevoix, Mich., from ‘‘26”’
Lake, Twin Lakes and Susan Lake, small inland lakes in the.
vicinity, and from Round Lake, opening into Lake Michigan,
and also from Intermediate Lake at Ellsworth, Mich., 116
specimens of U/. /uteolus, M. rugosa, A. subcylindracea Lea, A.
footiana Lea, A. edentula Say and A. fragilis Lam.

August, 1894, in two small lakes on Beaver Island, L.
Michigan, 85 specimens of U. luteolus, A. footiana, A. fra-
gilis and A. marryatana Lea.

July and August, 1895, from Grand River and smaller
streams, and from Reed’s Lake, near Grand Rapids, Mich.,
273 specimens of U. coccineus, U. gibbosus, U. ventricosus,
U. occidens, U. rectus, U. undulatus, U. plicatus Lea, U.
alatus, U. ligamentinus Lam, U. spatulatus Lea, U. Nowi-
eboract Lea, U. rubiginosus Lea, U. pustulosus Lea, U. School-
craftii Lea, U. verrucosus Barnes, U. luteolus, M. rugosa, WM.
marginata Say, A. ovata, A. edentula, A. footiana, A. sub-
cylindracea, A. fragilis, A. imbecilis Say.

July, 1897, from Rogue River, Kent County, Mich., and
from Reed’s Lake, Grand Rapids, Mich., 21 specimens of U.

NORTH AMERICAN SPECIES OF THE GENUS ATAX 199

occidens, U. spatulatus, M. deltoides, M. marginata, A. foot-
tana, and A. subcylindracea.

August, 1895, at Long Lake, Kalamazoo, Mich., 13 speci-
mens of U. luteolus, U. ventricosus and A. footiana.

August, 1895, at Black Lake, Holland, Mich., 10 specimens
of U. luteolus and U. ventricosus.

July and August, 1898, from various localities along Grand
River, near Grand Rapids, Mich., from the mill-pond at Mill
Creek, near Grand Rapids, from Reed’s Lake, and from Plas-
ter Creek, in the same vicinity, 534 specimens of the species
previously enumerated from the same localities, with the
addition of U. pressus Lea.

August, 1898, at White Lake, Muskegon county, Mich., 86
specimens of U7. luteolus, A. subgibbosa Anth., A. subcylindracea,
A. footiana and M. complanata Barnes.

August, 1897, at Lake Winnebago, Oshkosh, Wis., 21
specimens of U. gracilis, U. luteolus and A. grandis Lea.

October, 1894, from Blue River, Crete, Neb., 2 Unio
luteolus.

Octeber, 1894, from pools near Lincoln, Neb., 19 speci-
mens of U. parvus Barnes, U/. subrostratus Say, U. jamesianus
Lea and A. grandis.

October, 1894, from Platte River, South Bend, Neb., 1
A. grandis.

October, 1894, from Weeping Water Creek, Weeping Water,
Neb., about 50 specimens of U7. subrostratus, U. rubiginosus,
UO. undulatus, U. jamesianus and M. complanata.

September, 1895, from the same locality, 24 of the same
species.

September, 1895, from near Lincoln, Neb., 20 UW. lachry-
mosus Lea, A. plana Lea, and A. decora Lea.

September, 1897, from the Blue River, at Milford, Neb.,
42 specimens of U. lachrymosus U. ventricosus, U. School-
craftit, U. anodontoides Lea, M. complanata, A. plana and
A. grandis.

Thus, personally, the author has examined nearly 1,600

200 ROBERT H. WOLCOTT:

specimens of Unionide, representing a large number of locali-
ties and 39 species.

Through the kindness of Mr. R. H. Johnson of Harvard
University the material obtained from the following mussels
has been received for examination:

Angust, 1897, from Lake Chautauqua, New York, 150
specimens of UU. phaseolus Hild., U. gibbosus, U. luteolus, A.
edentula and A. plana.

August, 1897, from Cayuga Creek, Cheektowaga, Erie
county, N. Y., a number of UW. occidens. .

To Prof. H. M. Kelly of Cornell College, Mt. Vernon, Iowa,
the author is indebted for the data and mites obtained from
the examination of the following large number of mussels, col-
lected during the years 1896 and 1897:

From the Illinois River and bayous and lakes near Havana,
Ills., 731 specimens of U. alatus, U. asperrimus Lea, U. ang-

dontoides, U. cornutus Barnes, U. donaciformis Lea, U. ebenus~

Lea, U. ellipsis Lea, U. graniferus Lea, U. elegans Lea, JU.
gibbosus, U. Higginsti Lea, U. gracilis, U. laevissimus Lea,
U. ligamentinus, U. luteolus, U. lachrymosus, U. metanever,
Raf., U. multiplicatus Lea, U. parvus, U. pustulatus Lea,
U. pustulosus, U. rubiginosus, U. plicatus, U. securis Lea,
U. tenuissimus Lea, U. trigonus Lea, U. rectus, U. tuberculatus
Raf., U. ventricosus, M. rugosa, M. marginata, M. confragosa
Say, I. complanata, A. imbecilis, A. plana, A. suborbiculata
Say, A. edentula and A. corpulenta Coop.

From the Spoon River at Bernadotte and Duncan’s Mills,
Ills., 194 specimens including the greater number of the above
species.

From Abbey Creek and Cedar River, Mt. Vernon, Iowa,
486 specimens, including also the majority of the same species.

From the Susquehanna River at Lewisburgh and Sunbury,
Pa., and the Schuylkill River and French Creek near Phoenix-
ville, Pa., 202 specimens of A. edentula, M. undulata, M.
marginata, U. complanatus Sol., U. heterodon Lea, UO.
nasutus, U. ochraceus Say and U. tappanianus Lea.

NORTH AMERICAN SPECIES OF THE GENUS ATAX 201

Mr. M. Ricker of Burlington, Iowa, has kindly sent a small
collection of mites obtained at Havana, Ills., from the same
species of Unionide enumerated in the above list.

The present paper embodies, thus, the results of the exami-
nation of nearly 3,500 mussels, representing 60 species, and
from them have been collected and preserved about 7,000
mites, belonging to 13 species, of which 7 are new and 3 more
are reported from America for the first time. Search has been
made for mites in Pisidiwm and Spherium but with success in
only one instance, when two individuals of A. crasszpes (Miiller)
were found in a species of Spherium, and in Campeloma,
Physa, Limnea and Goniobasis, but so far without results.

In this enumeration and throughout the paper the author has
avoided any attempt to pass judgment upon the validity of the
different species of mussels referred to, and has included many
names which he himself believes to be synonyms, as for
instance, Unio occidens Lea and U. ventricosus Barnes, in order
that there should be in this way no omissions of species which
others might believe distinct from those given. All the
names given have been more or less generally recognized and
the reader is requested to make his own synonymical corrections
in accordance with his opinions.

The specimens of mites obtained were studied alive, pre-
_ served in various fluids, and mounted upon slides to allow of
thorough microscopical examination. Without, at first, suf-
ficient knowledge of the weight of specific characters, too much
dependence was placed upon color, which, it is found, has
almost no value in identification, though the brilliancy of
coloration is one of the principal features which make the group
such an exceedingly attractive one for study. Later certain
structural characters were fixed upon, which, by their similarity
in allied species, led to confusion; and differences, too, which
were at first assumed to be sexual, were found later, when the
true sexual characters were discovered, to be specific. Finally,
especially at first, the mites coilected from a single species of
mussel and bearing a close resemblance were assumed to be
identical and only found to include more than one species after

902 ROBERT H. WOLCOTT:

the accumulation of individuals in vials prevented the correc-
tion of the recorded notes. These, together with a lack of that
familiarity with the Unionide necessary to make sure identifi-
cations at the time of examination and consequent occasional
confusion in the recording of observations, impair the value of
early notes and collections. The facts are mentioned that
others may be warned thereby, and in order that certain allusions
in the descriptions which follow may be understood. It may
be said here, that in the case of more recent collections, care
has been taken to keep the mites from each mussel separate
until careful examination under the microscope, of the structure
of palpi, legs, genital area, etc., has allowed of exact identifi-
cation of each individual mite.

As to preserving fluids, alcohol, corrosive sublimate, picro-
sulphuric, Flemming’s and other solutions were at first used.
Of these corrosive sublimate gave the best results, but all have
been rejected as making the specimens too brittle and leading
to serious breakage of appendages. Formol does not preserve
the color effectually and is partly open to the same objections.
Yet a certain proportion of the specimens collected have always
been preserved in either it or the media previously mentioned,
to allow of their being studied in various ways. A solution
recommended by Koenike (91c) and consisting of

Glycerine.) 5... 2.0 Se ee parte yo ae
Distilled water... 2.5. 04), 3 Sparts byeole
Glacial acetic acid. 2...°..°9.". .....|22 parts! by vole
Absolute \aleohol os) 5.00551 1 part (by avolk

has been found to preserve the specimens in the best conminne

for future study, since although it cannot be recommended as a

preservative either of form or color, it keeps the body soft and

the appendages pliable, and thus they lend themselves the more

readily to methods of preparation used in making slide mounts.
A solution consisting of

Giyeerine® . (0. . hee .10 parts by weight,
Citric acid, pencenteated seleitae 3 parts by weight,
Distilled water................10 parts by weight,

to which is added, when the mites have regained their plump

NORTH AMERICAN SPECIES OF THE GENUS ATAX 203

form after being first shrivelled by being put into the mixture,
Absolute alcohol.........1—-10 of the total volume,

is recommended by Koenike (96) as an improvement over his

previous formula, and has been of late used in place of it,

without sufficient time having elapsed to judge of its merits.

In the preparation of slide mounts, specimens are removed
from the preservative, thoroughly washed in distilled water,
treated with a dilute potassium hydrate solution, a rent made
in the skin and through it the contents of the body pressed out,
again thoroughly washed, passed through the grades of alcohol
and clearing mixture and finally mounted in balsam. By this
means a perfectly transparent mount is obtained and all the
hard parts are readily studied. There is more or less distor-
tion, but comparison with specimens preserved in other media
assists in obtaining a correct view of the relations of the hard
parts, which are themselves in perfect condition. The mouth-
parts are removed from the body, separated by dissection and
also mounted for detailed examination.

The study of the material collected has resulted, as before
stated, in the detection of 13 species, of which 7 are new and
have been briefly described in a preliminary paper published in
the Zoological Bulletin for June, 1898. The list is as follows:

1. Atax crassipes (Miiiler).

2. Atax aculeatus Koenike.
3. <Atax pectinatus mihi.
4. Ataxr intermedius Koenike.
5. Atax abnormipes mihi.
6. Atax indistinctus mihi.
7. Atax serratus mihi.
8. Atax fossulatus Koenike.
9. Atax stricta mihi.
10. <Atax areuata mihi.
11. Atawx ypsilophorus (Bonz).
12. Atax tumidus mihi.

13. Atax (Najadicola) ingens (Koenike).
In the arrangement of these species in the order given, an
attempt is made to preserve the sequence in which the Eu-

9204 ROBERT H. WOLCOTT:

ropean forms have usually been arranged and with the end in
view of bringing allied species together. First the two free-
living forms, together with a third, parasitic in habit, but re-
sembling the other two very closely in form and structure, fall
naturally into what may be called the crass¢pes group, A.
crassipes, A. aculeatus and A. pectinatus. Then the forms in
which the hind leg of the male is modified and in which, in
the same sex, the body is more or less strongly emarginate
posteriorly and which in both sexes have the distal segment of
the palpus broad and tipped with two prominent curved claws,
form a second group, the intermedius group, including A.
intermedius, A. abnormipes, A. indistinctus and A. serratus.
A third group includes A. fossulatus and A. stricta, with 5
acetabula on each side, in the female set into the surface of the
body, in the male on a genital plate; while A. arcwats, A.
ypsilophorus and A. tumidus form a not very homogeneous
group, the members of which are related in form of body,
_ character of genital area, etc., and which in structure and po-
sition of the genital area show a gradual transition towards A.
(V.) ingens, which itself is related on the other hand to
Cochleophorus.

In the descriptions which follow, the terms used need no
explanation except perhaps with reference to the palpi and legs;
the former are supposed to be extended parallel to the long
axis of the body, whence the terms inner and outer, dorsal, ex-
tensor or upper, and ventral, flexor or lower, as applied to the
corresponding surfaces. The legs are supposed to be at right
angles to the body and the terms anterior and posterior become
applicable. The names applied to various parts are such as
have hitherto been applied or are literally translated from the
corresponding terms in use by European writers on the subject.

Measurements have been taken with an ocular micrometer.
The length of the body is that of the body proper, and the
projecting mouth-parts are not included; the length of a seg-
ment is the length of a straight line connecting the middle
points of its two ends; and the total length of an appendage is
the sum of such lengths of the segments which compose it. In

NORTH AMERICAN SPECIES OF THE GENUS ATAX AUS)

all measurements of legs which follow the claw is not included
in the total. For the sake of brevity the legs and the epimera
corresponding are frequently referred to by Roman numerals
and the segments of the legs and palpi are numbered from the
base outward, using Arabic numerals; thus ‘‘III 3” refers to
the third segment of the third pair of legs, and ‘‘Palpus 5” to
the distal segment of the palpus.

DESCRIPTION OF SPECIES.

I. ATAX cRASSIPES (Miiller).

Hydrachna crassipes Miller, 1776; 189, no. 2254: id., 1781; XLI, Pl.
Verh) 2.

Trombidium crassipes Fabricius, 1792; II, 400.

Atazx crassipes Fabricius, 05; 366: Koch, 35; 7, 21: id., 37; III, 8, Pl.
PES 1.

Atax elegans Koch, 35; 7, 12.

Atax truncatus Koch, 35; 7, 22.

Ataz albidus Koch, 35; 7, 23.

Atax confluens Koch, 35; 7, 24 (nymph).

Atax truncatellus Koch, 35; 37, 17 (nymph).

Hydrachna crassipes Walckenaer and Gervais, 44; III, 197.

Atazx crassipes Bruzelius, 54; Pl. I, f. 1-4: Claparéde, 68; 471: Kramer,
75; 293: Lebert, 79; 368, Pl. XI, f. 10, 10a; Neuman, 80; 21, Pl. I, f. 1:
Koenike, 81a; 627: id., 81b; 356: Haller, 81a; 76: Berlese, 82; fasc. LV, no.
7: Krendowsky, 85; 55: Barrois and Moniez, 87; 5: Piersig, 94b; 214:
Koenike, 95a; 139: id., 96a; 232: Piersig, 96; 40: id., 97; Lief. I, 52,
Pl. III, f. 5, a—h.

Atax crassipes is noteworthy among the species of this genus, for the
great length of its legs, which cover a greater area than those of any other
species, though its body is smallerthan many others. The body of the male
varies in length from 0.5 to 0.7 mm., while the female is from 0.7 to 0.9 mm.
and even 1.1 or 1.2 mm. long. Its form is broadly oval, with the larger
end of the oval anteriad and evenly rounded, the smaller end posteriad
and truncate, projecting nipple-like papillae at either side giving this end
the appearance of having been cut squarely off. The greatest breadth is
about opposite the third epimeron. The nipple-like papillae exhibit
varying degrees of prominence and Piersig describes a muscle which serves
as a retractor and by which they may be made to completely disappear.

The double eyes are very large, blackish in color, close to the margin
and moderately distant from each other, in a specimen 0.618 mm. long
being 0.184mm. apart. The anterior portion of each eye is larger and
nearly twice as large as the posterior.

206 ROBERT H. WOLCOTT:

The mandibles are nearly typical in form, though a little longer than
the average for the genus, the maximum width being equal to about one-
third the length, which in the specimen just referred to is0.148mm. The
greatest breadth is near the posterior end; the dorsal margin is slightly
concave, the posterior dorsal angle rounded, the posterior ventral angle
produced, forming a point of muscle attachment, and the ventral margin
nearly straight; a shallow mandibular groove is present. The distal seg-
ment includes about one-third the total length, and most of this is made
up by the slightly curved and rather slender claw, which is indistinctly
hooked at the tip and marked on the inner side toward the base by
slightly curved oblique striae, which are vertical to the line of insertion
of the claw.

Palpi, long and slender, segment 1 about half as thick a3 it is long: 2
the thickest of all and nearly as thick as long; 3 about two-thirds as thick
as 2, and a little over half as long; 4, longest of all, but only about half as
thick as 2; 5 slender, curved, at the base nearly as thick as 4, but at once
strongly contracted and throughout most of its length with the dorsal and
ventral surfaces nearly parallel. From above or below the palpi appear
even more slender than from the side, the extreme width of 2 at about
the middle being only three-fourths of its thickness and the palpus ta-
pering gradually and evenly from this point to the tip which is blunt and
bears very small claws; 2 has two small spines on the outer side close to-
gether and near the dorsal margin, and one on the inner side near the
middle, with a second very small one close to the base; 3 has a very long
stout spine in the middle of the outer side and one smaller but still long
and stout on the dorsal side near the distal margin.’ On 4 are the three
papillae characteristic of the genus, the two being but alittle beyond the
middle of the segment, the third at the distal margin, and all three being
exceptionally long and slender. The outer of the two is the longest and
its length equals the thickness of the segment, the third at the distal end
is about two-thirds as long as the outer, and the inner of the two only
about one-third aslong. The twobear each a small hair, the third a broad
chitinous cap. There is, finally, a long slender hair on the outer side of
this segment near the base.

The maxillary shield, as far as its main portion is concerned, is broad,
short and evenly rounded posteriorly, with a rather prominent rostrum
anteriorly; the ancoral process is nearly as long as is the main portion,
is broad at its base, its lateral margins forming with the anterior part of
the margin of the former a nearly straight line; and tapers to a narrow
tip, which is produced to either side forming recurved hooks.

The epimera are rather large, especially the posterior group, and the
spaces between the groups are narrow in the male, wider in the female.
The posterior margin of the anterior group is strongly convex while at
one- third the distance from the inner to the outer end and opposite the ~
suture between I and II, the two give rise to a long curved process which
runs back to a considerable distance beneath III. The separation be-
tween III and IV is represented by a line at about two-fifths the distance
from the anterior margin and which curves from the outer side obliquely

NORTH AMERICAN SPECIES OF THE GENUS ATAX 207

- inward and forward about half way acrosss the plate formed by the two.
This plate is nearly rectangular, somewhat longer than broad, with the
anterior margin slightly concave, and the inner slightly convex. On the
thickened border at the inner posterior angle are two hairs.

The legs, as before stated, are very long, all considerably exceeding
the body in length. Measurement of several specimens show a variation
in the relative length of legs and body and in the relative lengths of the
legs themselves, but this variation seems to possess neither locality, sexual
nor specific significance. In asingle specimen from Lake St. Clair the
third pair of legs exceeds in length the first, but in all other cases III is
the shortest, nearly equalling I, and Il and IV are considerably longer,
with IV a little longer than II and more than twice the length of the body.
In all cases the order of length of the individual segments in II and II]is
as follows, beginning with the longest—, 4, 6, 3, 2, 1; in I, 5 and 6 are of
about equal length, and both shortened, being shorter than 3; in IV, 6 is
lengthened and surpasses 4. In the case of I, 2 possesses a ventral
papilla, projecting chimney-like to a distance equal to two-thirds of the
thickness of the segment, deeply excavated and open at one side and re-
ceiving into this excavation a long movable spine, while there is also a
short movable spine at the outer margin of the posterior side; 3 has two
movable spines on either side ventrally; 4, four in two ranks on the
proximal half of the ventral surface; 5 a row of four towards the base
and one at the tip on the ventral side, of the former the first and third
being the longer. All of these spines are widest at a little distance from
their insertion tapering gradually to a blunt tip, and more rapidly to
their point of insertion. The fifth segment has the dorsal surface pro-
duced forming a scoop-like shield over the insertion of the next segment.
1, 2 and 3 are very stout, 4 tapers considerably towards the tip, 5 and 6
being noticably slenderer and 6 somewhat curved. II, III and IV are
slenderer at the base than I, and taper gradually from base to tip; they
possess a moderate number of long, slender, straight spines which form
groups on the tips of segments II 5, III 4, III 5, IV 4 and IV 5, while on
IV 3, numerous spines are scattered along the ventral surface. On I the
claws are rather stout, much curved and bifid, the ventral of the two tips
being the stouter; on the other legs, however, the claws are longer, much
more slender and the two tips are long, slender and sharply pointed,
while the dorsal of the two is not so long as the other and thus forms an
accessory Claw arising at a distance from the tip equal to one-fourth the
length of the claw.

The genital cleft in the female is flanked by four chitinous plates, of
which the two anterior are irregularly rectangular with rounded angles
and the two posterior roughly triangular with the angles also rounded.
Each bears three acetabula and numerous slender spines, and six longer
and stouter spines are borne—two each by the anterior plates and one
each by the posterior—on their contiguous angles which are somewhat
produced and directed outward. The male also possesses twelve
acetabula but they are borne on two lunate plates, one on either side,
and are distributed on each plate in two groups of three each.

208 ROBERT H. WOLCOTT:

On either side of the genital area isa large nipple-like papilla, which
varies in prominence, and which, according to Piersig, can be retracted
by a muscle running to it from the last epimeron. Koenike (81b) believes
these papillae to contain highly developed epidermal glands.

MEASUREMENTS,
Male. juv. Male Female Female
Grand Rapids, Mich. BeaverlI’ds. BeaverI’ds. Lake St. Clair.
Length of body, 0.367 mm. 0.701 mm. 0.835 mm. 1.002 mm.
Length of leg I, 0.683 mm. 1.234 mm. 1.357 mm. 1.596 mm.
Length of leg II, 0.842 mm. 1.525 mm. 1.657 mm. 2.081 mm.
Length of leg UI, 0.632 mm. 1.193 mm. 1.285 mm. 1.632 mm.
Length of leg IV, 0.872 mm. 1.596 mm. 1.708 mm. 2.112 mm.
Length of palpus, — 0.357 mm. 0.393 mm. 0.403 mm.

Atax crassipes was first met with Sept. Ist, 1893, in ma-
terial dredged over a bed of Chara in Anchor Bay, Lake St.
Clair, at a depth of about 3 meters. Specimens were again
secured near the same locality on the 3d, and in that vicinity
again on the 12th, at a depth of 5 meters. It was collected in
the southwestern part of the lake on the 8th and 10th at
depths of 5 and 6 meters respectively, and off Point Pelee
Island, Lake Erie, on the 17th, at a depth of 5 meters. Alto-
gether 29 specimens were secured. It appeared to be of
general distribution over the Chara which carpets the bottom of
Lake St. Clair, a lake which though of an area of 410 sq. miles
is over its deeper portion only about 6 meters in depth.

During the summer of 1894, specimens, parasitic as well as
free, were collected at several points in Northern Michigan.
They were found in Round Lake at Charlevoix, July 9th to
13th, at depths of 16 to 18 meters, in limited numbers; July
31st a specimen was secured in bottom collections from Lake
Michigan off Fisherman’s Island, a few miles west of Charle-
voix, at a depth of about 10 meters, and on August 18th
the species was obtained in bottom tows in Lake Michigan
between Beaver and High Islands at depths of 10 and 233
meters. Aug. 6th the species was found at Twin Lakes and
‘¢96°’ Lake, small inland lakes near Charlevoix, on Aug. 21st
at Susan Lake, another similar lake in the vicinity, and in
material collected on the same day at Intermediate Lake, also
not far distant. Sept. 5th Dr. R. H. Ward collected specimens

NORTH AMERICAN SPECIES OF THE GENUS ATAX 209

at Dodge Creek, Emmet County, so that the species may be
accounted as generally distributed throughout the smaller in-
land lakes of Northern Michigan, and also in Lake Michigan
and the smaller lakes in connection with it, though present
nowhere in large numbers. Mr. Bryant Walker, a concholo-
gist and a member of the same party as the writer, turned over
to him two specimens of an Ataxw from Spheriwm simile Say,
collected in ‘¢26” Lake Aug. 6th, and on the 17th of Angust
specimens of adults and nymphs were secured in considerable
numbers from Anodonta footiana and Anodonta fragilis taken
in a lake at the north end of Beaver Island, Lake Michigan.
All of these have been carefully studied from mounts and the
author has been unable to detect any characters by which any
of them may be distinguished from Atawx crassipes.

Specimens were collected at Grand Rapids, Mich., during
the months of July and August, 1896 and 1897, in Reed’s
and Fisk’s Lakes, and in a third very small lake near the city.
The former are lakes of moderate size and with a depth of 20
meters or more, but the latter is hardly more than a pool in the
midst of a cranberry bog, 50 meters across, and with scarcely
more than a meter of clear water above the loose, half-floating,
semi-decayed vegetable mould which forms the bottom of such
lakes. All are spring-fed. Two specimens, apparently of this
species, were collected in two examples of Anodonta fragilis
from Reed’s Lake, July 23, 1898.

From Mr. J. B. Shearer have been received specimens col-
lected in Quannecussec River, an arm of Saginaw Bay, Lake
Huron, in the Kawkawlin River, an affluent of the same bay,
and at Les Chenaux Islands, in northern Lake Huron, near
Mackinaw, all obtained during August, 1895.

In Wisconsin, the author has collected this form in Lake
Winnebago, at Oshkosh, Sept. 2, 1897, while he has received
it from two localities in Nebraska,—in a collection made by
Dr. H. B. Ward at a lake at South Bend, Sept. 2, 1897, and
from material obtained by Mr. O. D. Noble ina ‘‘stagnant
spring-fed pool”’ at Linwood, Sept. 1898.

14

210 ROBERT H. WOLCOTT:

2. ATAX ACULEATUS KOENIKE.

Atax crassipes juv. Claparéde, 68; 471, Pl, XX XIII, f. 1-3.
Atax aculeatus Koenike, 90; 138: id., 95d; 386, f. 13: Piersig, 96; 40,
footnote: id., 97; Lief. I, 59, Pl. I, f. 3.

A. aculeatus is very closely related to A. crassipes and can best be
described by comparing it directly with that species. It is similar in form,
but so far as the author’s observation goes never reaches as great size, the
males attaining a length of from 0.5 to 0.6 mm., the females 0.65 to
0.75 mm.

The mandibles are similar in form as is also the maxillary shield. The
eyes are very large, black and rather close together.

The palpi share in the resemblance, though they are apparently a
trifle more slender and are proportionately longer.

The epimera occupy even more of the under surface of the body and
in the male the four groups are almost in contact.

The legs are very long asin A. crassipes and the proportions similar,
though those of A.aculeatus seem slightly stouter than in the allied
species. The sixth segment is, however, somewhat longer in III and
exceeds 4. In I, 4 is the longest and 5 and 6 approximately equal to each
other, while both exceed 3; 6 is also not quite so slender as is the case
in A. crassipes and is less curved and a little dilated at the tip. The -
arrangement and length of the spines on the legs are practically the same
in the two species. The claws are similar.

The genital field in the present form is characteristic and markedly
different from that of A. crassipes. There are but ten acetabula instead
of twelve, in the male situated on two kidney shaped plates which flank
the genital cleft. On each side two anterior acetabula are placed one directly
behind the other, and are separated by an interval from the three pos-
terior, of which the two anterior lie side by side. The cleft is longer than
in A. crassipes and in the case of all specimens on slides gapes widely.
In the female the single lateral plate is divided into two, the anterior of
which is pouch-shaped with the neck of the pouch directed anteriad, while
the posterior is similar in outline but inverted. The former has two
acetabula, the latter three. The ovipositor is prominent and of character-
istic form. From each side of the genital opening projects a plate which
anteriorly and—since the genital area is on the posterior surface of the
body—also, ventrally, is produced and turned outward forming a conical
process, at the top of which is articulated a short, thick, sharply-pointed
spine. At the base of this, internally, is a small sharply-pointed process,
and from the posterior—and dorsal—margin projects a longer, tapering
and sharply pointed process, both of these processes being not set into
sockets, but apparently continuous with the rest of the plate. By the
apposition of these two plates, they are able, probably, to serve together
as an ovipositor.

NORTH AMERICAN SPECIES OF THE GENUS ATAX 211

At either side of the genital area is a conical papilla, similar to that
found in A. erassipes but still more prominent.

MEASUREMENTS.
Male Female

Lengthvotiroadigs 62/39 Sasi Mole 0.601 mm. 0.668 mm.
Length on erie ans i. os la este 0.943 mm. 1.244 mm.
LP sjakeqne coy \l 2;=, 10 a Re a 1,168 mm. 1.453 mm.
Bengthro ieee cs. 62/90.) Sa gate 0.918 mm. 1.147 mm.
Leng thtarlergeyee ai ee elke ya 1.199 mm. 1.601 mm.
Leng thie fe pansy tibiae 0.301 mm. a

In the examination of mussels from Grand River, at Grand
Island near Grand Rapids, Mich., July 9, 1896, nymphs of
different species of mites and also dead mites were found in
the mucous about the exhalent aperature of many individuals.
Little notice was taken of these until in Unio ligamentinus, U.
alatus and Anodonta edentula, afew adults were found; these
were, however, on cursory examination, supposed to be Atax
crassipes. A more thorough examination later showed them
not to be that species and to belong probably to Atax aculeatus,
a determination which has since been verified. On the 5th of
July, 1897, six specimens were found along the edge of the
mantle of Unio spatulatus from the Rogue River, Kent County,
Mich. During the past summer especial care was taken to ex-
amine all mites and nymphs occurring in the situations referred
to. It was found that most of them were nymphs and of these
the majority were A. abnormipes, a smaller number were A.
aculeatus, a still smaller, A. intermedius, and now and then
one of A. serratus or A. fossulatus, all of these species being
reared from such nymphs. Of all, only A. aculeatus was rep-
resented by adults, while this species in its adult form seemed
to occur nowhere but along the margin of the mantle and about
the exhalent and inhalent aperatures, situations which its
slender form and superior activity enable it to maintain. The
mussels from which it was obtained were U/. rectus, U. gibbosus,
U.. undulatus, U. ligamentinus, U. oceidens, U. ventricosus, U.
spatulatus, U. Novi-eboract, U. coccineus, all from different
localities along Grand River, north of the city of Grand Rapids,
Mich. ; Unio pressus and Anodonta plana, from Plumb’s Creek,

919 ROBERT H. WOLCOTT:

near that city; and Undo luteolus, from White Lake, Muskegon
County, Mich. The dates were from July 27th to August 30th.

38. ATAX PECTINATUS WOLCOTT.

Atax pectinatus Wolcott, 98; 280.

A species, in the character of the genital area allied to A. crassipes
and A. figuralis Koch, but with the legs relatively shorter than either and
with the palpi very thick, considerably thicker than the basal segment of
the first pair of legs. The claw of this pair of legs is broad, flat and
deeply pectinate, which character suggests the specific name.

It is of medium size as compared with the other species of the genus,
the males measuring 0.7 to 0.8 mm., the females 0.8 to 1.0 mm. in length
respectively. ‘he body is broadly elliptical with the antero-posterior
diameter but slightly greater than the transverse, which is greatest at a
point about midway between the anterior and posterior extremities. The
posterior margin is smoothly rounded and the surface is uniformly
smooth and without chitinous thickenings of any kind. The males are
somewhat slenderer than the females.

Eyes moderate in size, with the anterior of the two lenses the larger.

Maxillary shield relatively short and broad, with a prominent rostrum
formed by the apposed anterior mesial angles of each of the two max-
illary plates which are completely fused anteriorly. The posterior lateral
angles are quite evident though rounded while the ancoral process pro- —
duced by the apposition of the two produced posterior mesial angles is, as
compared with other species, very weak.

Mandibles with a long, narrow proximal segment which is slightly
broader posteriorly where it is directed somewhat ventrad and tapers to
a bluntly rounded point, in front of whichis ashallow mandibular groove.
Its form is irregular owing to the undulating marginal outline. Distal
segment large, with a broad basal portion and a sickle-shaped claw which
is moderately curved except toward the tip, where the curvature is more
pronounced and where it tapers somewhat more rapidly than before to a
sharp point. The proximal half of this claw is marked by fine, wavy,
oblique lines. Extreme breadth equal to about one-fourth its total length.

Palpi large and heavy, those of the female somewhat more than two-
fifths the length ofthe body. ‘Those ofthe male are very little smaller than
those of the female in absolute measurement and are therefore larger in
proportion to the size of the body. Basalsegmentshort and broad. Segment
2 is the largest and much the thickest, equaling nearly one-half the total
length and with a thickness in proportion to the length as 5:9. The flexor
side is nearly straight, with a very slight concavity, the extensor side very
convex and evenly so, making it much longer than the other and causing
the planes of the two ends to be very oblique to one another. On the
inner side of segment 2 are two flattened spines rather near together, at
a distance from the basal margin of about one-third the length of the seg-
ment, and a third one-half the distance from these to the distal end, all
three being nearer the extensor than the flexor side of the palpus. On

NORTH AMERICAN SPECIES OF THE GENUS ATAX 913

the outer side are two toward the extensor margin, the distance between
them somewhat less than one-third the length of the segment. Segment
3 is much shorter than 2 and not so broad, yet broader than long. Its
flexor side is half the length of the extensor, each of them with a slight
convexity, and there is a small straight spine on the outer side, while 4 is
longer and narrower, concave on its flexor surface, moderately convex on
the opposite side. The former bears distally a pair of not very prominent
papillae and a short spur at the distal margin. Segment 5 tapers at first
rapidly, then more gradually to a blunt, rounded tip, produced slightly
toward the flexor side and bearing at the distal end four short claw-like
projections arranged in quadrille, while immediately proximad of them
are two very short spines.

Epimera covering about the same proportion of the ventral surface as
do those of A. figuralis, but Il and II] and those of opposite sides are
separated only by very narrow spaces, narrower in the male than in the
female. Outline of the fused I and ILapproximately triangular, the apex
of the triangles of the two sides nearly meeting in the median line. The
anterior margin of this triangular plate is slightly excavated and the
posterior forms a double curve, being convex for the inner two-thirds of
its length and beyond that concave. I is long and narrow, broadly ex-
panded at its outer end, where it is moderately excavated to receive the
first pair of legs, while Ilis broadly triangular with the anterior external
angle truncate. The plate formed by the fused III and IV has a slightly
concave anterior margin, a nearly straight inner margin, and a posterior
margin slightly convex, all the angles being rounded. The epimera of
the opposite sides approach each other most closely in front. A trans-
verse suture two-fifths of the distance from the anterior to the posterior
margin indicates the line of junction of the two epimera.

The legs are shorter than in the related species and relatively longer
in the male than in the female. In the former I is slightly longer than
the body, II and YI about equal and each a little less than one-third
longer, [V about two-thirds longer. I of the female is almost four-fifths
of the body length, Il and III somewhat exceed it and IV is greater by
a little more than one-third. Of the individual segments 1 is the shortest
and the others gradually increase in length to 5, but 6is again shorter. I
is slightly heavier than the rest, though as a whole the legs are decidedly
weak and the distal segments especially slender. There are no movable
spines on I set into projecting sockets as in A. crassipes and A. figuralis,
their number is somewhat less, and individually they are shorter and
more slender and taper to a sharp point. The claws are characteristic.
Those on I are expanded dorso-ventrally and flattened laterally, forming
a broad plate of which the dorsal margin is strongly arched, the flexor
margin deeply pectinate, the pectinations, about sixteen in number, reach-
ing nearly three-fourths the distance to the opposite margin, and with a
slight curvature toward the base of the claw. The claws of the remaining
legs are slender, strongly curved at the base, more moderately beyond,
and again more strongly toward the sharply-pointed tip. On the whole
the claw of II has the more pronounced curvature and is shortest, IV the

914 ROBERT H. WOLCOTT:

least pronounced and is longest. Each has a very inconspicuous tooth in
the middle of the flexor margin.

The genital area is circular in general outline and is situated toward
the posterior end of the body. It includes a genital cleft, flanked on
either side in the male by one genital plate, in the female by two. The
genital plates of the male are each lunate in form and bear six acetabula
placed in two groups with a moderate interval between. In the female a
transverse division along this line separates each plate into two, of which
the anterior is irregularly quadrilateral, the posterior roughly triangular
in outline, each bearing three acetabula.

MEASUREMENTS OF SPECIMENS DESCRIBED:

Male Female

length of bodily. i. .\ji-yey- lle 0.70 mm. 1.08 mm.
Length of palpus............ ae 0.44 mm.
Mengthiomles ee celery. 0.73 mm. 0.82 mm.
Kengthvot leg Ty ie te) 1.00 mm. 1.14 mm. (approximate)
hength of leo Ie: 0.98 mm. 1.15 mm. a
Mength.of Leg UV iiie ae msars lt: 1.18 mm. 1.41 mm.
Length of mandible. ........ —— 0.292mm.
Length of genital area, me-

diamwelefiic ic neve ae neerice 0.21 mm. 0.17 mm.

Types retained in the collection of the author.

This species was taken in the dredge at Lake St. Clair, Sep-
tember 1, 1893; later another was discovered in material
collected a few days previous; and others were afterward col-
lected in the vicinity of New Baltimore, Mich. Altogether six
specimens were secured, but owing to breakage in transit of the
bottle containing them, only two are available for description,
and these, a male and a female, are to a certain extent distorted
in mounting. Field notes taken at the time say: ‘‘ Pinkish
tinge to epimera and genital area. Legs and palpi blue of an
unusally deep tint. Body deep olive brown, with a yellowish-
brown Y-shaped mark. Eyes blackish.”

4. ATAX INTERMEDIUS KOENIKE.

Atax ypsilophorus van Beneden, 48; 9 et seq., Pl.

Atax Bonzi ‘‘ living free,’’ Koenike, 81a; 626.

Atax intermedius Koenike, 82; 265: Lampert, 93; LXXIX: Piersig,
94b; 214: Koenike, 96a; 233: Piersig, 96; 40: id., 97; Lief. I, 46, Pl. I,
f. 2, a-e.

A. intermedius is one of the smaller species, and especially small are
the males, between which and the females there is a much greater dif-
ference in size than in any other of our species. The length of several of

NORTH AMERICAN SPECIES OF THE GENUS ATAX 215

each sex, measured from preserved specimens, proved to be from 0.75 to
0.95 mm. for the females and only about 0.5 or 0.6 mm. for the males.

The form is broadly oval, approaching elliptical, and with both ends
evenly rounded. The skin shows a fine, even, parallel striation over the
whole body of the female; the striae running transversely, while the
epimera show the hexagonal reticulation which is characteristic of the
group of species which has been referred to as the intermedius group. In
the male the same reticulation is visible over the whole body, but is more
pronounced and regular on the epimera.

Eyes large and rather distant from each other.

Maxillary shield relatively broad, especially posteriorly, where its
thicker portion is evenly rounded, while the thinner and relatively slender
ancoral process extends posteriad a short distance and ends in a broad
tip, which is produced laterally to an unusual degree, forming recurved
hooks. Line of separation between the two plates of which the shield is
composed distinct.

Mandibles quite typical in form, the basal segment rectangular,
broader posteriorly, with the dorsal posterior angle rounded, ventral pos-
terior angle produced and a shallow mandibular groove on the ventral
side. Distal segment moderate, claw rather small and slender, and
moderately curved.

The palpi are as a whole quite slender, being only a little thicker than
the first pair of legs, and in many respects are characteristic. The basal
segment is not unusual; but 2 is much longer along the dorsal margin than
along the ventral, the former being moderately convex, the latter nearly
straight. It bears on the outer side and near the dorsal margin three long
slender spines, two close together near the middle, a third toward the
distal margin; on the opposite side are two spines near the middle. 3 is
nearly straight along the dorsal margin, slightly convex along the ventral,
and about half as long and two-thirds as thick as2; it bears a long, slender
spine on the outer side close to the proximal margin, and one on the
inner side, close to the distal margin and also to the dorsal surface. 4 is
the longest of all, yet only half as thick as 2; its dorsal margin is slightly
convex toward the base and nearly straight beyond; its ventral surface is
concave proximally, but convex distally where it bears the usual number
of papillz, of which the paired ones are characteristic. The outer of the
two is short and inconspicuous, the inner very large, prominent and
flattened laterally; in the male the latter is longer and slenderer, while the
former is also longer. Both bear smallhairs. Segment 5 is curved ventrad
and is nearly circular in cross-section at the base, but at the tip is com-
pressed laterally; it bears the usual terminal claws, which, however, are
only moderately large and the whole segment is unlike that in the other
species grouped with this.

Epimera in the female occupying about the anterior half of the ventral
surface, in the male nearly the whole of it, leaving only room posteriorly
for the genital area. Spaces between the groups also much wider in the
female than in the male. In the former the first epimeron is nearly rect-
angular, and II irregularly triangular, with the inner end produced and

216 ROBERT H. WOLCOTT:

passing beneath the anterior margin of III. Of the posterior group, II
comprises about one-third and the suture between it and IV runs obliquely
inward and forward half way to the inner margin. Anterior margin
slightly concave, inner and posterior slightly convex, with inner posterior
angle rounded and those of opposite sides diverging. In the male all the
epimera relatively much larger and the inner ends of the anterior groups
nearly in contact. The posterior groups are not only nearly in contact
but a chitinous bridge connects the two which thus become one mass
which is somewhat emarginate posteriorly.

The legs are all longer than the body in the female and very much
longer in the male. IIJis the shortest, I next longer, II next and IV the
longest of all. They are of medium stoutness and taper slightly from
base to tip. In I and II the three outer segments are, in order of length,
beginning with the longest, 4, 5, 6; in IIT all are nearly equal, but 5 exceeds
4; and in IV, 6 is also longer than 4. The spines are moderately
numerous on the legs of the female and are rather long, while those on 2,
3 and 4 of I are set into short excavated papille similar to those of A.
crassipes, though ‘not so prominent. A bunch of four or five spines on
the proximal half of the ventral surface of I 4 is noticeable. On the
ventral surface of 4 and 5 of both III and IV, there are numerous hairs,
more abundant and smaller on IV than on III, longer at the tip of each
than elsewhere. The legs of the male posess fewer spines than do those
of the female, and in this sex IV is peculiar; 4 of this leg is curved, the
concavity being on the posterior and ventral aspect of the segment, and .
at the tip on the same aspect is a bunch of very long spines. On the
posterior surface of 5 and about the middle isa bunch of strong, feathered
spines. The claws are similar in form to those of A. ypsilophorus, and
as in that species, are received into a cleft in the end of the dilated tip of
the segment.

The genital area is proportionately large and flanked in the male by
one plate on each side, in the female by two. Each of the two in the male
is broadly lunate in form and bears five acetabula in two groups—?2 and 3
respectively—and numerous small spines. In the female the anterior
plate on each side is rhomboid in shape, with the anterior and outer mar-
gins slightly convex, and the posterior concave; it bears two acetabula,
which are larger than those of the male, and its inner margin is reflected
outward, forming two blunt, moderately thick lips, the margin of each of
which bears two short stout spines. The posterior plate is roughly circular
with a projecting inner anterior angle and its anterior and inner margins
are thickened, the inner also reflected, forming a broader and less promin-
ent lip than that of the anterior plate, while at the inner anterior angle
is a stout spine, and external to it on the anterior margin a second. On
this plate are three acetabula.

NORTH AMERICAN SPECIES OF THE GENUS ATAX ING

MEASUREMENTS:
Male Female
| Drerokes fw) Kon 13/0105, So ROTO Le Sai 0.501 mm. 0.752 mm.
Hen gthtaimlea yy cca Weleis ae ol alye 0.643 mm. 1.112 mm.
Ben gthrommleme eventos). aaicidaele oe 0.852 mm, 1.607 mm.
Heng thvar leash oe yon) ee 0.627 mm. 0.959 mm.
Beng thiomereiy ss cago a 0.867 mm. 1.571 mm.
Menethion palpusn is) co cs es: 0.214 mm. 0.337 mm.

Of this species, 13 specimens were obtained at L. St. Clair,
Aug: 17, 1893, from Anodonta ovata and Oct. 10, 1893, 22
specimens were collected at Lansing, Mich., from mussels
taken from Cedar River, but unfortunately the record of species
of Unionide has been lost. It was found in considerable
abundance at Round Lake, Charlevoix, Mich., in Anodonta
subcylindracea, A. footiana, A. edentula and Unio luteolus;
at ‘¢26” and Twin Lakes, in A. edentula, A. footiana and A.
Sragilis, in limited numbers in the former but more abundantly
in the latter lake; and at Intermediate Lake, in Margaritana ru-
gosa, Anodonta subcylindracea, A. footiana, A. edentula and
A. fragilis, but in none common. At Beaver Island, Lake
Michigan, it was collected rather commonly in Anodonta
footiana and A. marryatana taken from a lake towards the
south end of the island. At Grand Rapids, Mich., during the
summer of 1895, A. intermedius was found only in Marga-
ritana rugosa from two localities on Grand River and only in
limited numbers, while during the past summer the same was
found to hold true. A few specimens were secured Aug. 17th
to 20th, 1898, at White Lake, Muskegon County, Mich., from
Anodonta footiana and A. subcylindracea.

In Nebraska it is a very abundant form, and on one occasion
a very large Anodonta plana was fouud to contain 406 speci-
mens. It has been collected in ponds at Lincoln, in Weeping
Water Creek at Weeping Water and in the Blue River at
Milford, from Unio subrostratus (once), U. Jamesianus (once),
Margaritana complanata (occasionally), Anodonta plana, A.
decora and A. grandis. The females are almost uniformly in
excess, averaging three to each male; of 1178 specimens from
the vicinity of Lincoln for example, 275 were males and 893,

218 ROBERT H. WOLCOTT:

females. There is usually a tinge of blue in the Michigan
specimens, lacking in those from Nebraska.

5. ATAX ABNORMIPES WOLCOTT.

Atax abnormipes Wolcott, ’98; 280.

Among the species to be considered in this paper are two which are
quite different from all others, which bear a very close resemblance to
each other and which are yet clearly distinct. They are both peculiar in
the possession by the males of a highly modified fourth pair of legs, while
the females present no marked structural peculiarity. The first of these
is Atax abnormipes. It is one of the smaller species, the females aver-
aging about 0.7 mm., the males about 0.55 mm. The body of the former
is about one-sixth longer than broad, somewhat broader posteriorly and
so slightly pyriform in shape and evenly rounded at both ends. In pro-
file it is about two-thirds as high as long, flattened dorsally in the center,
the outline descending abruptly at either end. The surface of the body is
marked by lines dividing it into minute hexagonal areas, appearing
facetted. ‘The male is decidedly pyriform, with a breadth equal to four-
fifths its length, the average of a number of specimens being 0.445 mm.
and 0.56 mm. respectively. The body is smoothly rounded: anteriorly,
but deeply emarginate posteriorly.

Eyes very large, in the male measured, 0.143 mm. apart. Each lens
nearly circular, the anterior a little the larger.

Maxillary shield —Comparatively broad, the sides anteriorly nearly
parallel, with the anterior lateral angles diverging. The ancoral process
very broad with a width at the tip of over half the extreme breadth of the
whole, inconspicuously hooked and with sides which from the tip di-
verge at once to the posterior lateral angles, which thus instead of ap-
pearing posterior, seem like projecting angles in the middle of each side.

Mandibles.—The basal segment is broadly rectangular, nearly as
broad as long, slightly narrowed anteriorly, the dorsal posterior angle
rounded, the ventral angle produced for attachment of muscles. Distal
segment comparatively large, the claw rather heavy, slightly curved and
quite blunt. Patch of oblique striae near its base sharply limited and
witha broadly elliptical outline.

Palpi.—Whole palpus slender and somewhat less than one-half the
length of the body. Basal segment short, while 2 is of moderate length,
relatively thicker than the rest, and convex along both extensor and flexor
margins, the convexity of the former the greater; on the outer side are two
long, tapering, slightly curved spines toward the extensor margin; on the
inner surface one, similar to the others, in the middle, and a second close
to the distal margin. 38, somewhat narrower than 2 and proportionately
ong, though hardly as long as broad; flexor margin nearly straight;
extensor margin convex; aspine at the proximal margin of outer surface,
nearer the extensor side, and another at the distal margin on the inner
side. 4, long and slender, narrower than 3, about three times as long as
thick and slightly tapering toward the end; paired papillez on the flexor

NORTH AMERICAN SPECIES OF THE GENUS ATAX 919

margin two-thirds the way towards the tip, short, and with a slender
spine, the third at the distal margin short and inconspicuous. 5%, broad,
laterally quadrate in outline, with the ventral distal angle produced and
on the distal margin two slender, strongly curved claws, one near the ex-
tensor margin, the other about in the median line.

Epimera large, covering most of the uuder surface of the body and
with a very narrow space between II and III and between those of oppo-
site sides. I, rather broad, with parallel margins, the anterior margin
concave, the posterior slightly convex. II, slightly broader than I and
with its posterior margin quite convex and forming with the inner end of
Iacontinuous curve. Line of separation between III and IV distinct one-
half the way in from the lateral margin and one-fourth the distance from
the anterior towards the posterior margin of the plate formed by the two.
Anterior margin of III concave and anterior internal angle projecting.
Posterior margin of IV strongly convex, indistinctly angulated, and pro-
duced backward to a point even with the genital area, which thus lies in
an angle between the last two epimera. Lateral margin deeply excavated
between the points of articulation of legs III and IV and opposite the
division between the corresponding epimera. The surface of the body
between the four groups of epimera is thickened and so to a certain ex-
tent all are fused into one mass. The surface of all the epimera is
marked, as is the rest of the body surface, by a system of lines cutting it
up into small hexagonal areas, and the same is true of the maxillary
plates.

Legs.—In the male, very short and comparatively thick, the last
especially so. [averages one-seventh shorter than the body and is
shortest of all, III is one-seventh longer than the body, II a sixth longer
and IV a fourth longer. Of the individual segments, 1 is shorter, 2 and 3
are about equal and next longer; 4 is longest except in IV where 6 is very
long, exceeding it and all the others; while in I and II, 6 exceeds 5 and
in III the reverse is true. The legs are all moderately well supplied with
spines and are not noteworthy except in the case of III, 5 and IV, 4 to 6.
The former has at its tip three doubly curved blade-like spines reaching
three-fourths the way to the end of 6. Of the latter, IV 4 is compressed
laterally through the distal two-fifths of its length and on this compressed
portion bears a bunch of six very large spines, placed in two rows on the
ventro-anterior surface, and exceeding in length the next segment, while
on the posterior surface are about nine spines, of which six are moder-
ately stout, while the three distal are very long and slender and reach
beyond the distal end of 5 by about one-third its length. 5 is short, at its
base narrower than 4, tapering toward the tip, with two very heavy,
curved blunt spines on the extensor surface and a row of spines along the
flexor side, and a bunch of fine hairs at the distal end, while 6 is very
slender and ratherlong. All the claws are strongly bent and bifid, withan
accessory tip on the convex side short and inconspicuous and ending at a
distance from the end equal to one-sixth the whole length of the claw.

220 ROBERT H. WOLCOTT:

The legs of the female are slenderer and relatively shorter and II] much
shorter than inthe male. IV, 4 is exceeded by both 5 and 6. There is no
marked structural peculiarity; the segments of the last pair decrease reg-
ularly in thickness from 1 to 6; 1V 4 lacks the six large spines; and IV 5
the two long ones, retaining the row of spines on the flexor surface.

The genital area of the male lies one-half on either side of the groove
in the emarginate posterior end of the body, the opening being at its bot-
tom; the latter is bounded by two rather broad lunular plates, each with five
acetabula in two groups—two in front and three behind. In the femalea
transverse division indistinctly separates each of these lunules into two
parts, the anterior with two, the posterior with three acetabula, and each
bears at the angle adjacent to the other three, a flattened spine.

MEASUREMENTS:
Female Male
Meng thy OL wociye ies sae sic aicie lester . 0.714 mm. 0.586 mm.
Meng Lato leo ein es vena. weve tise 0.560 mm. 0.510 mm.
Lengthiot ler eet: ea eesepae 0.740 mm. 0.688 mm.
ene thiol Leg We ee il .s cae 0.663 mm. 0.668 mm.
engthvoiles ly sabe ttc ake eee 0.770 mm. 0.745 mm.
BAUS Alen eee aie fete oi ere sia 0.306 mim. 0.265 mm.
Mandi ple st vacate te eeherson «esata 0.173 mm. 0.153 mm.

Types in the author’s collection; co-types have been deposited in the
collection of the Zoological Laboratory, University of Nebraska, in the
Museum of Comparative Zoology, of Harvard University, in the United
States National Museum, and in the Kgl. Museum fir Naturkunde in
Berlin.

Atax abnormipes was collected at Lake St. Clair during the
summer of 18938, but owing to confusion of different species
due to lack of familiarity with the group, no statement can be
made as to the hosts except that it was almost surely harbored
by Unio alatus, U. ventricosus and U. luteolus. It was next
met with at Grand Rapids, Mich., in the summer of 1895,
when individuals were found in U. ligamentinus, U. occidens,
U. ventricosus (very abundant), U. alatus and U. rectus from
different localities in Grand River, while collections made since
have added to the list of hosts U. undulatus, and emphasized
the fact that it is far more abundant in UW. ventricosus than in
any other species of mussel. One specimen was found in that
species from Rogue River, Kent County, Mich., July 5, 1897.
It has been taken in limited numbers in UJ. luteolus from
Reed’s Lake near Grand Rapids, Mich., in the same Unio
from Long Lake, Kalamazoo, Mich., and in that and U7. ventri- -

NORTH AMERICAN SPECIES OF THE GENUS ATAX 221

cosus, from Black Lake, Holland, Mich., while the past summer
it was found in U. luteolus from White Lake, Muskegon County,
Mich.

At Oshkosh, Wis., the species was found during September,
1897, in U. gracilis and U. luteolus from Lake Winnebago.
In Illinois, as determined from specimens received from Prof.
H. M. Kelly and Mr. M. Ricker, A. abnormipes has been taken
from U. anodontoides, U. gracilis and U. occidens collected at
Havana. Finally in material received from Mr. R. H. Johnson
and obtained at Chautauqua Lake, N. Y., it occurred in U.
luteolus and U. phaseolus and perhaps in Anodonta plana,
though the record is doubtful, while it also was present in

mites taken from U. ventricosus at Cheektowaga, Erie County,
me Y.

6. A. INDISTINCTUS WOLCOTT.

Ataz indistinctus Wolcott, 98; 281.

The second species of Atax referred to under the head of the preced-
ing is A. indistinctus, which received the name it bears when only
females had been collected, and in reference to the close resemblance be-
tween the females of the two species, which were only separated by the
most careful observation. Since the preliminary paper in which this was
described has been published an abundance of males have been secured
and the species shown to be entirely distinct though closely allied.

A. indistinctus is a species rather under medium size and yet a little
larger than A. abnormipes, the measurement of several males showing a
variation in body length of from 0.675 mm. long by 0.55 mm. broad to 0.75
mm. long by 0.618 mm. broad, while the average of a number of females
was 0.€25 mm. by 0.63 mm. It is similar in form to A. abnormipes, and
like that species the whole surface of the body is marked off by fine lines
into smal] hexagonal areas.

Eyes large but not quite so large as in the preceding species, and
about the same distance apart.

Maxillary shield similar to that of A. abnormipes, but the posterior
lateral angles not so prominent and the sides in front of it slightly diverg-
ing instead of parallel. Rostrum rather prominent.

Mandibles similar to those of A. abnormipes in form.

Palpi rather slender but not so much so as in those of the previous
species. The spines are similar in number and position to that form, the
two on the outer side of 2 dividing it into thirds. The distal margin of
this segment is not uniformly concave but a shallow re-entrant angle
separates the extensor two-fifths and the flexor three-fifths of its length.
A rounded angle in the proximal margin of 8 corresponds to this, the
segment being proportionately heavier than in the allied species, while 4 is

929 ROBERT H. WOLCOTT:

also proportionately stouter and more tapering, its base being nearly as
thick as that of 3, while the distal end is only one-half as thick as the
proximal; its breadth in the middle is a littleover one-half its length. The
papillae on this segment are rather more prominent than in A. abnormipes.
5 is similar to that of that species but the claws are more slender and a
little farther apart, and the ventral distal angle a little more produced.

Epimera.—Of the same general character as in A. abnormipes, but
differing in the following respects: They occupy sligatly less than a pro-
portionate amount of the ventral surface; the space between the groups of
epimera is a little greater and the inner ends of the first pair do not
approach closely to each other but leave a considerable interval behind
the maxillary shield. This is owing to a shortening of I and is accompa-
nied by an increase in the curvature of the posterior margin of the plate
formed by it and IJ, which margin is also indistinctly angled toward the
base of II. The posterior margin of IV does not project so far posteriorly
and so the genital field is not to such an extent enclosed by it.

Legs of female relatively longer than in A. abnormipes and very
slightly more slender. I is one-tenth shorter than the body, II and III
about one-fifth longer and of the two, II a trifle the longer, IV two-fifths
longer than the body. Individual segments of each leg in order of length
4, 6, 5, 3, 2, 1, except in IV, where the last three are 6, 5, 4. Number and
distribution of spines on the legs about the same as in A. abnormipes; a
row of long spines on the flexor surface of segments 4 and 5 of leg IV; the
tip of 5 in each leg armed by several long spines.

In the male, I slightly exceeds the body-length; II, III and IV are each
alittle over two-fifths longer, and of these IV is slightly longer than II and
that slightly longer than III. Segments in I and II, in order of length 4,
6, 5, 2, 3, 1; in III, 5 is longer than 6, and in IV, 6 is less than 2 or 3, this
shortening leading to a shortness of the whole leg. The same three
spines are present at the distal end of IV 5, but are not so long—not quite
two-thirds the length of 6. IV modified in a similar manner to the same
in A. abnormipes, but differing in the following details: Spineson 3 much
more numerous; on the posterior surface of 4 the spines are longer and
more numerous, and on the ventro-anterior surface are eight spines, three
in a dorsal and five in a ventral row; the distal portion of this segment is
not so much compressed, and the ventral surface is quite evenly convex;
5 is thicker, has a row of ventral spines as in A. abnormipes but only one
long heavy spine in the middle of the dorsal surface instead of two.
Claws similar except that the accessory tip is one-third the length from
the end of the principal one.

Genital area as in A. abnormipes in form except that the angle which
separates the plates of the two sides anteriorly is more acute here than in
A. abnormipes. Acetabula in males usually seven on each side—in one
specimen eight—with an indefinite separation into two groups. In the
female are three and six on the two plates of either side, in one case four
and five on one side and three and six on the other.

ail nue

NORTH AMERICAN SPECIES OF THE GENUS ATAX 223

MEASUREMENTS:
Maile Female
eng th Oh ody, wut ye oe.) oie +00 0.740 mm. 0.867 mm.
Width of body (extreme)....... 0.637 mm. -——_.
Meng thi oth le ey ye 4) (bs c)acss ehetee 0.785 mm. 0.698 mm.
Length ofplesa iby. sie.) (sce. ss 1.066 mm, 0.890 mm.
Hengthiaileme My oc. 5 5/0/54 1.050 mm. 0.870 mm.
Bengthioh leo Vee so.) aja 453s 1.076 mm. 1.020 mm.

Palpus (from another speci-
men of same size in case
C09 ig 0062113) jr ae: 2 a 0.347 mm. 0.380 mm. (approx.)

Types in the author’s collection; co-types have been deposited in the
collection of the Zoological Laboratory, University of Nebraska, in the
Museum of Comparative Zoology of Harvard University, in the United
States National Museum, and in the Kgl. Museum fiir Naturkunde in
Berlin.

Specimens of females of this species taken at Lake St. Clair,
Mich., were confused with the following species and their
identity not detected till mounted and subjected to a careful
microscopical examination, when the differences between the
two species became apparent. Hence no statement can be
made as to the definite source of the specimens.

It was therefore with much pleasure that upon looking over
the collection of mites from Prof. H. M. Kelly, this species
_was found in considerable numbers—60 males and 115 females
altogether. They were taken from JU. alatus and U. gracilis
from the Illinois River at Havana, Ills.; from UW. gracilis from
the Spoon River at Duncan’s Mills and Bernadotte, Ills. ; and
from ‘‘Unio spp.” from the Cedar River at Mt. Vernon,
Iowa. Specimens were also found in the material from Mr.
M. Ricker.

7. ATAX SERRATUS WOLCOTT.

Atazx serratus Wolcott, 98; 282.

Atax serratus resembles very closely the two preceding species in the
appearance of the palpiand in the form of the claws and to a lesser degree
in the outline of the genital field and of the epimera. It is larger, pro-
portionately more elongated and the body of the male is only slightly
pyriform. The legs are proportionately shorter and IV of the male is not
modified. They are characterized by the presence of numerous serrate
spines which suggests the specific name proposed.

The body is oval in form, bluntly and evenly rounded at both ends in
the female, that of the male with a slight posterior emargination. Its

994 ROBERT H. WOLCOTT:

extreme width at a point a short distance beyond the middle is equal to
two-thirds of the length; from the side the dorsal convexity is seen to be
considerable and quite uniform, but highest posteriorly. Its surface is
smooth and without chitinous thickenings or lines of any kind, though
the epimera show the regular reticulation referred to in regard to the
two preceding species.

Eyes as in the two preceding forms, large and deep black in color,
though a little farther apart than in the others.

Maxillary shield similar to that of the preceding; suture between the
two plates running about half way forward from the posterior end and a
little farther than even with the posterior lateral angles.

Mandibles.—Ventral margin nearly straight; dorsal parallel to it,
curving outwardly however toward the posterior end, and this curve con-
tinued evenly around the posterior end to the produced posterior ventral
angle. Distal joint medium in size and not noteworthy as to form; claw
slightly curved, and concave margin slightly arched outwardly in middle.

Palpi large and heavy, similar to those of the preceding in form.
Convex dorsal margin of 2, two and a half times the length of the nearly
straight flexor margin and 2 one-third as broad as the length of the whole
palpus; there are two spines near the middle of its outer surface, one on
the inner near the middle and another near the distal margin which is
flat, blade-like and serrate. 3 very broad, its breadth four-fifths that of
the preceding and one-half its length; inner margin one-half of outer and
both nearly straight. 4 thick, considerably tapering, at the base two--
thirds as broad as 2 and at the tip less than one-fourth as broad. Paired
papillae three-fourths the distance to the distal end. 5 has the inferior
distal angle produced and a spine at the base of the projection on the
outer side.

Epimera occupying two-thirds of the ventral surface, with the spaces
between the groups narrow; the inner ends of the anterior groups ap-
proach each other much closer than in the preceding, and the posterior
margin, instead of being smoothly rounded, shows an excavation oppo-
site the junction of the two epimera. Anterior median angles of posterior
groups produced, anterior margin concave; the inner margins diverging
posteriorly; the posterior median angles rounded off; and the posterior
margin convex, but only moderately so. Suture separating III and IV
nearly complete.

Legs moderately heavy, rather more slender than in the other two
species and proportionately shorter, while the species is peculiar in the
fact that III is longer than IJ. In the male I equals about three-fourths
the body length, II is somewhat shorter than the body, III about equal
to it, while IV, which is shortened, is only one-tenth longer. In the fe-
male_all the legs are relatively shorter still and IV is scarcely longer than
the body. Length of individual segments in order, beginning with the
longest, 4, 5, 6, 2, 3, 1, except in III where 5 is about equal to 4and in IV
of both male and female where 5 is greater than 6 and that than 4. In
the female more or less of the spines on the legs are serrate along both

,

NORTH AMERICAN SPECIES OF THE GENUS ATAX ID5

margins, those on only the basal segment of I, but gradually including
more and more on each leg, till on IV are serrate spines on all seg-
ments, and on the distal is arow of very prominent, flattened, blade-like,
serrate spines. On IV 4 are also three heavy club-shaped spines. In the
male serrate spines are present, but less numerous and not so prominent,
while the sex is characterized by not only the shortening of the last pair of
legs but also by a thickening of the same making them stouter than the
two preceding pairs and about as stout as the first. Theclaws are sharply
curved, have an accessory tip at two-thirds the distance from the base,
and end in a very fine point.

Genital area broader than long, each lateral plate divided in the
female into two, an anterior pouch-shaped plate with its inner end pro-
duced into along neck, curved backward and bearing on its tip a flattened
spine, and a posterior nearly circular plate. Three specimens examined
possessed the following number of acetabula: 15 and 31 on one side, 12
and 25 on the other; 11 and 21 and 12 and 19; 8and 12 and 6 and 17. The
male has but a single plate on either side with a total of 19 or 20 acetabula
on each side.

MEASUREMENTS:

Male. Female.
Bength ote bodys. Wie ol oo ue ae 0.868 mm. 1.170 mm.
ene tho pliers Nia ae uly eines 0.668 mm. 0.816 mm.
Renetinoieleo LE t 0.5 sibs salcy sue 0.820 mm. 1.020 mm.
Meriathiatwlec (Ty yo yl \chaicle g 0.870 mm. 1.070 mm.
Berne RTM £.) sitio iunian a skal 0.959 mm. 1.214 mm.
Bengt Ob pal pus. 13) 22 3 eis. a's \s —- 0.510 mm.

Color of legs, a bright blue-green, and body tinged with bluish-green.

Types in the author's collection; co-types have been deposited in the
Zoological Department, University of Nebraska, in the Museum of Com-
parative Zoology of Harvard University, in the United States National
Museum, and in the Kg]. Museum fiir Naturkunde in Berlin.

Of A. serratus, specimens have been collected at L. St.
Clair, probably from Unio luteolus. At Grand Rapids, Mich.,
specimens have been obtained from Unio coccineus, U. undu-
latus and U. alatus from Grand River, and from Margaritana
deltoides from Rogue River, Kent County, Mich. In material
from Unio occidens from Cayuga, Cheektowaga, Erie County,
N. Y., one specimen was found, while specimens have been
secured amongst a number of mites from ‘* Unio spp.” col-
lected in the Cedar River, Mt. Vernon, Iowa. It is thus a
widely distributed species, though one of the rarer ones. Owing
to an accidental interchange of the marks ‘‘3” and ‘*?” upon
the labels of two slides and the distraction of numerous inter-
ruptions when the preliminary description of this species was

15

926 ROBERT H. WOLCOTT:

written, confusion occurred in that description and so it is in
certain particulars wrong. Unfortunately too, and much to the
writer’s regret, the error was overlooked in the reading of
proof and only discovered after the separates were distributed.

8. ATAX FOSSULATUS KOENIKE.

Atax fossulatus, Koenike, 95b; 221, Pl. III, f. 68-70: Wolcott, 98; 283.

A. fossulatus is one of the larger species of the genus, the males
ranging in length from 1.1 mm. to 1:3 mm., the females from 1.4 mm. to
1.6mm. The body is oval, smoothly rounded anteriorly and posteriorly
and with the greatest breadth about opposite the posterior margin of the
last epimera; dorsally it is considerably arched, somewhat higher pos-
teriad.

The eyes are moderately large and quite close together, in one male
specimen 1.08 mm. long, the longest diameter of the eye amounting to
0.046 mm., and the distance between the inner borders of the two to 0.224
mm., while the extreme width of the body is 0.718 mm.

Maxillary shield broad, the sides anteriorly nearly parallel, the latero-
posterior angles moderate and the shield contracted posteriorly to a rather
broad and short ancoral process the width of which is two-sevenths the
greatest width of the shield.

Mandible with basal segment roughly rectangular, broadened pos-
teriorly, the dorsal and posterior margins forming, by the rounding off of
the posterior dorsal angle, a sweeping curve. Total length in the speci-
men referred to above, 0.28 mm. and greatest width somewhat more than
half the length. Distal joint moderate in size and with the claw compar-
atively short and straight, slightly hooked at the tip; the area of cross-
striae on the side of the base of the claw comparatively restricted.

Palpi rather large and moderately heavy, in the specimen referred
to previously the length amounting to 0.607 mm., while the maximum
dorso-ventral diameter of segment 2 is 0.184 mm. Segment 2 is convex
on both dorsal and ventral margins, but the dorsal curature is much the
greater; it is but little longer than thick, and bears on both outer and
inner surfaces two spines, those of the outer side close together midway
between the two ends and near the dorsal margin, those on the inner
side also close together, slightly farther from the base and more removed
from the dorsal margin. 3, about two-thirds as thick as 2, one-half as
long, and with a spine at the proximal margin on the inner side and
another toward the distal margin on the outer side. 4, slightly longer
than 2, slightly less than one-half as thick; the dorsal and ventral mar-
gins nearly parallel to the base of the paired papillae on the ventral sur-
face, beyond which the thickness of the segment rapidly diminishes. All
segments showing a gradual tapering when viewed from above. The
outer of the paired papillae is very small, the inner more prominent and
the spur at the distal margin moderately so. 5, nearly straight above,
concave below, tapering to a blunt tip, which bears three small blunt
claws; on the ventral margin, midway between base and tip, a small hair.

NORTH AMERICAN SPECIES OF THE GENUS ATAX 22%

Epimera covering approximately the anterior half of the ventral
surface of the body, the spaces between the two groups on either side
comparatively narrow, that between the groups of opposite sides greater,
especially in the case of the anterior groups, between the inner ends of
which is quite an interval. The spaces are all wider in the female and in
that sex the epimera are relatively a little smaller than in the male. The
last epimera are relatively long, being longer than broad, while just ex-
ternal to the inner posterior angle the posterior margin bears a spur-like
projection which curves outwardly and probably serves as a point of
muscle attachment. III, broadened externally, and an excavation on the
outer margin corresponding to the suture between it and IV.

Legs rather long and slender, the first considerably stouter than the
others; the first pair of the female nearly three-fourths the body length,
Il seven-eights of that length, III slightly exceeding the length of the
body, and- IV nearly a fourth longer. In the male the legs are propor-
tionately still longer, all exceeding the length of the body, I by a very lit-
tle, IV by over two-thirds. Of the individual segments, 4 exceeds 5 and
that 6, except in III, where 5 is longer than 4, and in IV where 5 is still
more elongated and 6 greatly lengthened, slightly exceeding 5. The seg-
ments gradually decrease in thickness from 1 to 6 and the last tapers con-
stantly from base to tip. The legs are armed with a considerable number
of spines of medium length, which form a continuous row along the
ventral surface of segments 4 and 5, and also along 6 in the case of IV,
the spines in this last case shorter. The distal segment is unusually con-
tracted toward the tip, and is not cleft to receive the claws, but these last
are partly covered by a thin chitinous plate, which, together with several
slender hairs, springs from the dorsal side of the segment behind the
claws. The claws are bifid, a small accessory claw being developed on
the dorsal side of the primary one very close to the tip, except in the case
of the first leg, where the secondary claw is longer and springs from a
point one-third the way back from the tip of the other. The claws, as a
whole, are rather heavy and strongly curved.

The genital area is situated about midway between the last epimera
and the end of the body, slightly nearer, perhaps, to the latter. It is
broadly oval in form and nearly as broad as long. In the male the
genital cleft is flanked by two reniform plates, which bear five large
acetabula, of which the two anterior are in contact, the second separated
by a narrow interval from the third, the three posterior in contact, and
the two last situated side by side; several short spines are found along
the inner margin of these plates. In the female the five acetabula bear
the same relationship to one another but the two plates are not so evident
and the acetabula seem to be set into the surface of the body itself, though
this is thickened over the whole by a deposition of chitin. At the genital
opening, short clefts in this thickened area run toward either side and in
the four angles formed by these and the genital cleft itself, are four short,
stout, curved spines, while other smaller spines occur here and there,
scattered over the space within the row of acetabula and along the mar-
gin of tae genital cleft.

998 ROBERT H. WOLCOTT:

MEASUREMENTS:
Male Female
ene Diol Om ye iiss eaie were. 1.1386 mm. 1.419 mm.
Menethi ot Mes ye cae els tsk 1.188 mm. 1.085 vim.
enoth ot vler Tinton ae seems 1.515 mm, 1.285 mm.
Mengthrot Veg MM rns a. va. tte: 1.647 mm. 1.438 mm.
Mength oiqleg TV ess eee ae eat) 1.958 mm. 1.739 mm.

This species was the most abundant of all at Lake St. Clair,
228 specimens being secured from a number of species of
Unionide, but no definite statement of the exact species in
which it was taken can be given, except that among them were
U. alatus, U. ventricosus and U. luteolus. .

Specimens were secured at Charlevoix, Mich., and vicinity,
as follows: in Round Lake, from Anod. subcylindracea, A. foot-
tana and U. luteolus; in ‘6267’ and Twin Lakes from the same
Anodontas and A. edentula and A. fragilis; in South Lake,
Beaver Island, Lake Michigan, from U/. luteolus. Nowhere
else has this species been found in Anodontas, and I should be
tempted to believe that those collected had migrated from Unio
luteolus while the mussels were kept in pails of water a day or
two before being examined, were it not that at Twin Lake only
Anodontas were collected. The species was rare at all of these
localities.

At Grand Rapids, Mich., A. fosswlatus has been found very
generaily distributed,—in Unio luteolus at Reed’s Lake; in U7.
rubiginosus, U. plicatus, U. undulatus, U. pustulatus, U. Now-
eboraci, U. occidens, U. ventricosus, U. ligamentinus, U. spat-
ulatus, U. rectus, U. coccineus, U. verrucosus (especially
abundant), (/. alatus, U. Schoolcrafti, from different localities
in Grand River; and in J. occidens from Rogue River, Kent
County.

The species has also been taken at Lansing, Mich., but from
what host is uncertain. At White Lake, Muskegon County, it
was found the past summer in U. duteolus, and at Black Lake,
Holland, Mich., it has been collected from that species and
from Unio occidens.

At Oshkosh, Wis., it has been found in Unio gracilis and
U. luteolus.

NORTH AMERICAN SPECIES OF THE GENUS ATAX 229

It is present in the material from Illinois in (. alatus, U.
asperrimus, U. cornutus, U. gracilis, U. pustulosus, U. plica-
tus and U. occidens from the Illinois river at Havana, and
from JU. gracilis, U. levissimus, U. lachrymosus, U. pustulosus
and U. tuberculatus from the Spoon River at Duncan’s Mills
and Bernadotte. Also in materia! from the Cedar River at
Mt. Vernon, Iowa, from U. rectus, U. alatus and others.

In New York it has been found at Chautauqua Lake in
luteolus and at Cheektowaga, Erie County, in U7. occidens.

9. ATAX STRICTA WOLCOTT.

Ataz stricta Wolcott, 98, 283.

Very similar to the preceding in many ways but differing in details.
It is smaller than A. fossulatus, relatively broader and the legs are not
only slenderer and shorter, but have usually a blue tinge which is lacking
in the otner species.

Eyes small and rather distant from one another.

Maxillary shield and mandibles very similar to those of A. fossulatus.

Palpi slenderer than those of that species and with the last segment
somewhat more strongly curved; ventral papillae on 4 relatively a little
more prominent.

Epimera in general of the same form. They are, however, slightly
broader proportionately, and the posterior median angle of IV is more
rounded and not so strongly excavated.

Legs relatively shorter, more slender and not so tapering as those of
the preceding species. I, notso noticeably stouter than the others and distal
segment, instead of growing constantly smaller toward the tip, is nar-
rowed in the middle and dilated at the tip, which is even slightly broader
than the base. Asin A. fossulatus, 5 is relatively elongated on III and
both 5 and 6 on the last pair of legs, and as in that species III is longer
than II. Distal segments relatively longer on all legs and last segment
flattened and very slightly dilated dorso-ventrally at the tip, instead of
gradually contracted as in A. fossulatus. Claws all simple, relatively
longer and more slender, and those on I stouter and not so evenly curved
as those of the other legs. Not so many spines on the legs as in the allied
form, but they are longer.

Genital area in about the same position as in the preceding but rela-
tively smaller, the acetabula smaller, and intead of the last two being side
by side they are all in one curved line. The two rows do not approach
each other so closely anteriorly and posteriorly as in the other species.
The sexes differ in a manner similar to those of A. fossulatus.

230 ROBERT H. WOLCOTT:

MEASUREMENTS OF A MALE:

MengthOlebod ya a2s)acinaie a eisieceters ets 0.835 mm.
Menoth on lee Leia alee tepeiesieete te 0.811 mm.
Lenethrot deo eee MN itso 0.995 mm.
Meneth Giles We icswiierieece ae 1.107 mm.
Mength ones eV: Cat Tarte: 1.250 mm.

No female is in such a condition on the slide as to allow of ready or
accurate measurement.

Types in the author’s collection; co-types have been deposited in the
Museum of Comparative Zoology of Harvard University, in the United
States National Museum, and in the Kgl. Museum fiir Naturkunde in
Berlin.

This species when collected was considered to be the male of
A. fossulatus, but when slide-mounts of that species were made
the true male was discovered, and also both sexes of the
present form. The most striking difference, and that first
noted, was in the position of the acetabula in one line, hence
the name ‘‘stricta,’’ but careful observation showed the
presence of other differences as above indicated and also that
these differences, though slight, were constant. It may be a
variety of A. fossulatus, but it is for the present considered
separate, though closely allied.

Specimens were taken at Grand Rapids, Mich., during the
summer of 1895, among A. fossulatus, from U. coccineus, U.
ligamentinus, U. occidens, U. rectus, U.rubiginosus, U. Sehool-
crafti, U. undulatus, U. verrucosus and U. alatus—89 speci-
mens altogether—but owing to their being confused with A.
Jossulatus no statement can be made as to the exact source.
Collections of many more of the same mussels from near the
same localities, this last summer, it was hoped would give more
definite information, but only one specimen was found, which
wasin U. undulatus.

In Nebraska it has been collected from U. Jamesianus and
U. lachrymosus from pools near Lincoln, from UW. undulatus,
U. lachrymosus, U. rubiginosus and U. Jamesianus at Weeping
Water, from Weeping Water Creek; and from U. lachrymosus
from the Blue River at Milford. The Nebraska specimens are
all peculiar in that the genital area is a little smaller and the

Voie

NORTH AMERICAN SPECIES OF THE GENUS ATAX 931

acetabula smaller and more closely crowded toward the middle
of either side.

Specimens were received from Prof. Kelly and Mr. Ricker
collected in U. plicatus at Havana, Ills.

10. ATAX ARCUATA WOLCOTT.

Atax arcuata Wolcott, 98; 284.

A species equal in size to A. fossulatvs and A. ypsilophorus, between
which it appears to occupy an intermediate position, having resemblances to
both, but quite distinct from either. It is especially characterized by the
form of the legs, the distal segments of which are so strongly curved as
to suggest the name bestowed upon it.

It is of the same elongated elliptical form which characterizes the re-
lated species, very slightly broader posteriorly, and with both anterior
and posterior margins evenly rounded.

Eyes very small and lenses nearly equal. In the male specimen
measured the two were 0.301 mm. apart.

Maxillary shield similar to that of A. ypsilophorus, except that the an-
coral process is not so long, and the lateral margins perhaps a little less
divergent anteriorly.

Mandibles of the same form as in that species except that a concavity
is present in the posterior margin toward the ventral angle, whereas in
A. ypsilophorus the margin is nearly straight.

Palpi also very similar to those of A. ypsilophorus, though varying
somewhat in the direction of those of A. fossulatus. 1, as heavy asin the
former species, but 3 relatively less thick, and 4, instead of tapering,
nearly as thick at its distal as at its proximal end, the ventral papillae
being more prominent. Distal segment slenderer and longer than in A.
ypsilophorus and the claws at the tip relatively smaller.

Epimera.—Anterior groups narrower toward the median line and
more nearly triangular than in either A. ypsilophorus or A. jossulatus.
Posterior group much shorter than in either and inner margin distinctly
shorter than the outer, with both anterior and posterior inner angles very
much rounded, especially the latter, which causes the epimera of the two
sides to appear widely divergent posteriorly. Space between the two
groups of epimera on each side very wide.

Legs very long, especially in the male, and similar to those of A. fos-
sulatus in that 1 is very markedly thicker than the rest and in that the
successive segments of each leg are distinctly slenderer than the one
next the body and give an evident tapering appearance. They are, how-
ever, relatively slender. III is a trifle longer than II, all but I exceed the
body in length, and IV is over half as long again. Of the segments, 5 is in
all legs unusually long and 6 abnormally short. The legs are less plenti-
fully supplied with spines than are those of either of the other two species
and the spines are rather weak, ‘The legs are especially characterized by
the curved form of the terminal segment, the curvature being only mod-
erate in the case of I, but in IV amounting to a deflection of 30°. This

932 ROBERT H. WOLCOTT:

segment also tapers toward the tip but just at the end is broadly ex-
panded to receive the short thick bifid claw, which is much smaller,
broader and thicker than in A. fossulatus. The rounded margin of the
expanded tip of the segment projects above the claw beyond its base, and
bears two short flattened lanceolate spines which project still farther.

Genital field similar in form to that of A. ypsilophorus though some-
what broader, being broader than long, like that of that species in posi-
tion, and finally also flanked in both sexes by a single plate on either side,
which bears in the male about 22 to 25 acetabula, in the female 26 to 30.
These are not all of the same size and two a little before the middle and
against the outer margin of the plate are decidedly larger than the rest.
Spines at the genital opening of the female similar to those of A. ypsilo-
phorus, heavy, curved and flattened. A few small and weak spines are
seen along the inner margin of each genital plate.

MEASUREMENTS:
Female Male
Length ol body. carat: +. . 1.170 mm. 1.250 mm.
Leneth of leg’ De ec cmaetirten) ss, caus 0.918 mm. 0.872 mm.
length oflep il eer cect 2 irene 1.4138 mm. 1.346 mm.
Dength: of lem sil te aoa e en eas oie. 1.454 mm. 1.382 mm.
Geneuh ot lep Viper enews ee 2.040 mm. 1.907 mm.
Lenvth of, palpusy. asa ee eee 0.403 min. 0.408 mm.
Length of genital field........... —__——— 0.224 mm.
Width of genital field.... ..... — 0.255 mm.

In color this species is not distinguishable from A. ypsilophorus.

Types in the author’s collection; co-types have been deposited in the
collection of the Zoological Laboratory, University of Nebraska, in the
Museum of Comparative Zoology of Harvard University, in the United
States National Museum, and in the Kgl. Museum fiir Naturkunde in
Berlin.

A. arcuata was first found at Charlevoix, Mich., in Round
Lake and living in Anodonta subcylindracea, A. footiana and
Unio luteolus. At ‘+26’? Lake it was collected in Unio luteolus
and at Intermediate Lake in Wargaritana rugosa, A. subcylin-
dracea, A. footiana, A. edentulaand A. fragilis.

At Grand Rapids, Mich., it has been taken in Marg.
deltoides, M. marginata and A. subcylindracea, and at Rogue
River, Kent County, in A. subeylindracea. At White Lake,
Muskegon County, Mich., it has also been found common in
A. subcylindracea and in all the collections referred to, far
more specimens were taken in that than in any other mussel.

It has been collected in Marg. marginata from the Schuyl-
kill River at Phoenixville, Pa., and specimens were received
from Prof. Kelly.

NORTH AMERICAN SPECIES OF THE GENUS ATAX 933

11. ATAX YPSILOPHORUS (BONZ).

Acarus ypsilophorus Bonz, 1783; VII, 52, Pl. I, f. 1-4.

Trombidium notatum Rathke, 1797; IV, 175, Pl. X.

? Hydrachna triangularis Say, 21; I], 79: id., Leconte’s Ed., 59; IT, 22.

Limnochares anodontae Pfeiffer, 24; pt. 2, 27-28, Pl. I.

Hydrachna concharum von Baer, 27; XIII, 590, Pl. X XIX.

Unionicola oviformis, U. lactea, ? U. personata, ? U. humerosa, ? U.
symmetrica, ? U. proxima, ? U. lugubris, ? U. wnicolor, ? U. reticulata—
Haldeman, 42; 1-3, Pl., f. 1-11.

Non Atax ypsilophora von Beneden, 48; (=A. intermedius Koenike).

Atax ypsilophora Garner, 64; 114: Claparéde, 68; 474, Pl. XX XIII:
Bessels, 69; 146: Lebert, 79; 367.

Atax ypsilophorus Neuman, 80; 26, Pl. I, f. 2: Koenike, 87a; 626:
Haller, 81a; 78: Koenike, 82; 265: Leidy, 83; 44: Harrington, Fletcher and
Tyrrell, 84; 140.

Atax concharum Krendowsky, 85; 59.

Atax ypsilophorus Barrois and Moniez, 87; 5: Girod, 89; XIV, n. 5,
107: Koenike, 91c; 257: Piersig, 94b; 214: Koenike, 95b; 217: Piersig, 96; 40:
Koenike, 96; 232: Piersig, 97; Lief. I, 43. Pl. I, f. 8, a-h.

This, the best known of all the species of the genus and the one first
described, is also one of its larger representatives, the males measuring
from 1.1 to 1.3 mm. in length, the females from 1.3 to 1.5 mm., or when
distended with eggs, 1.8mm. The body is oval, but more nearly elliptical
than in most species, evenly rounded at each end, and much arched. The
males are considerably slenderer than the females.

The eyes are proportionately small and moderately close together, in
a specimen 1.086 mm. long, 0.296 mm. apart. They are brownish black in
color.

The maxillary shield is widest anteriorly, quite evenly rounded pos-
teriorly and with a prominent ancoral process, which is considerably
broadened at the tip, each lateral corner of which is produced to form a
recurved hook. The rostrum is moderately prominent. Mandibles
relatively short and broad. in a specimen 1.32 mm. long, their total
length being 0.24mm. The basal segmentis broadest posteriorly, where
its width is over two-fifths the total length; its ventral side is nearly
straight, with the posterior angle produced; its dorsal and posterior side
form together a sweeping curve from near the anterior end on the dorsal
side to the ventral posterior angle. The distal joint is rather heavy, but
the claw is deeply inserted and the exposed portion is relatively short
and slender, and quite straight. The area of oblique striae is rhombic in
outline and confined to the base of the claw, which is bent at a point even
with the distal margin of the segment, and ends in a sharp point.

Palpi.—Comparatively small and only moderately thick. The first
segment is narrow, and 2 is wide, being twice as wide as 1, and wider than
long, measured from the middle of one end to the middle of the other.
Ventral margin slightly convex, the dorsal stronglyso. 3, short and mod-
erately broad with both sides nearly straight, while 4is of moderate length,

934 ROBERT H. WOLCOTT:

somewhat longer than 2, gradually tapering and with sides nearly straight.
The paired papillae on its ventral surface are a little over two-thirds the
way toward the tip and the claw at the distal margin is only moderately
conspicuous. 5 is rather small, curved, with the ventral side unusually
concave and the tip slightly broadened and bearing the usual claws,
which are here rather prominent. The inner side of 2 bears a spine near
the middle, and the outer side two in the middle and nearer the dorsal
margin; 3 has a spine at the basal margin on the inner side and one at
the distal margin on the outer; 4 has in addition to the hairs on the
papillae, two small ones on either side of the claw at the distal margin of
the ventral surface: and 5 has a hair on the outer side a short distance
from the base. Piersig (97) describes the hairs on the outer side of 2 as
feathered but I can discover no such on my specimens.

The epimera are quite typical. The anterior groups are quadrilateral
and the posterior rectangular with the spaces between them of consider-
able width, especially in the female, in which sex the posterior groups
are relatively shorter. The anterior groups have the anterior and pos-
terior margins nearly equal, the outer a little shorter and the inner still
shorter. lis nearly of equal breadth throughout and its inner end makes
up the whole of the inner margin; II] is triangular with both anterior and
posterior margins convex: while its inner end is prolonged into a short
eurved hook which turns backward and outward. III makes up only.
one-fourth of the length of the posterior group, which has a slightly con-
cave anterior margin, a nearly straight inner margin, a convex posterior
margin, and rounded angles.

The legs are of medium length, and rather slender, with the first pair
not much thicker than the rest. I in the female is nearly five-sixths of
the length of the body, II is about one-seventh longer than the body,
III is shorter than II and about equal to the length of the body, while
IV is more than a half longer than the body. In the male the legs are
relatively somewhat longer. Of the individual segments, 4 is longest and
the others follow in the order 5, 6, 3, 2, 1, except in IV where 5 is longest,
and it and 6 both exceed 4. All the legs are abundantly supplied with
hairs and spines, and many of them, especially on the middle segments
of the anterior three legs and at the tip of [V 5 are long and almost like
swimming hairs. IV has the ventral surface of 4 and 5 thickly beset with
spines of moderately length, and this pair of legs has, on the whole, more
spines, but they are shorter than in the preceding pairs. The distal end
of segment 6 on all the legs is broadened dorso-ventrally and receives in
a groove in it the thus retractile claw. ‘The claws possess two tips of
which the proxinal one is slightly curved and meets the distal tip whichis
in line with the basal portion of the claw, at a right angle. The distal
tip curves slightly for a short distance beyond the junction of the two,
and then turns sharply ventrad so that its outer end is nearly parallel to
the proximal tip.

Genital area flanked by two plates, each of which bears from 16 to 24
acetabula. The area in both sexes broader than long, each plate in the
female with a thickened strip running from the groove at the genital

NORTH AMERICAN SPECIES OF THE GENUS ATAX 935

opening outward toward the acetabula, but not reaching them. The two
plates in the male bear a few small spines and the margins next the
groove are not thickened or produced. But in the female, these margins
are thick, and produced outwardly in front of the genital opening to
form two wide lips, which diverge at their tips. These lips each bear
along their margins several spines, a small one anteriorly and two or
three longer, stouter and somewhat curved ones about the middle. Be-
hind the genital opening the lips are not so prominent and there is but a
single longer and more slender spine.

MEASUREMENTS OF A FEMALE:

Female
STU UREA NOC ye arsver fark 2 sie esti lis Li ccte Alay aronelabteatie ait as 1.536 mm.
IG Tise ole Grier OM erie y ants cere ye evenness wraiaiald Wate aaile/e 1.030 mm.
| oyeialyeaslalsCON? NEVE, LLIIAA bcs eee Stace tee Pe TE I eR 1.515 mm.
Prerategi a Cen le UE aad EN OAT a a ARO See 1.326 mm.
| Greravental sn dette NY ee AER A MS AN eS 2.147 mm.
LEH ODES 3 Oe itech tad yo eso EIR Oe Dan eg a LEE Ee Ue 0.495 mm

The number of previous records of the occurrence of this
species in North America is suchas toshow ita very common and
widely distributed form. Dana and Whelpley (36) found it at
New Haven, Ct., in A. Awwatilis Dillw, and in a second species
of mussel which they incorrectly identified as Unio purpuratus
Lam. Haldeman (42) seems to have collected it in A. fluvia-
tilis, U. radiatus and U. cartosus from the Susquehanna River,
Pa. Leidy (83) records it in A. flwwiatilis from Clarksboro,
N. J., and Koenike (95b) from Canada, in Anodonta fragilis.

It was found to be common in the summer of 1893 at Lake
St. Clair, in A. ovata, and also at Lansing, Mich., in the fall
of the same year though in what mussels is uncertain.

In Northern Michigan it was equally abundant the next
summer, being collectedin A. subcylindracea and A. footiana
from Round Lake at Charlevoix; from the same and also
from A. edentula and A. fragilis, from ‘267 and Twin
Lakes in the vicinity of Charlevoix; and in A. subcylindracea
and A. fragilis from Intermediate Lake at Ellsworth, Mich.

At Grand Rapids, Mich., it is abundant and has been col-
lected in numerous localities along Grand River, in U. pressus,
M. marginata, M. rugosa, A. edentula, A. ovata, A. subcylin-
dracea and A. footiana; from Reed’s Lake in A. fragilis; from
Rogue River, Kent County, in J. rugosa, A. ovata and A.

236 ROBERT H. WOLCOTT:

footiana; from Plaster Creek in A. ovata; and from the mill
pond at Mill Creek in A. plana and WU. pressus.

At White Lake, Muskegon County, Mich., it was collected
during the past season in A. subgibbosa, A. subcylindacea, A.
footiana and M. complanata.

In Illinois, it has been found in A. corpulenta and A. imbe-
cilis from the Illinois river at Havana and in A. suborbiculata
from Thompson’s Lake near Havana. In Iowa it has been
obtained in the Cedar River from M. rugosa at Mt. Vernon.
In Nebraska the writer has collected it in U. subrostratus and
A. grandis from pools near Lincoln; in J. complanata, A.
plana and A. decora from Weeping Water Creek, Weeping
Water; and in A. grandis, A. plana and M. complanata from
the Blue River at Milford.

From the material received from Chautauqua Lake, N. Y.,
it is apparently as common as in all other localities cited, and
has been collected in A. plana and A. edentula.

The record of collections shows that it is essentially an Ano-
donta parasite, though occuring in Margaritana and rarely in
Unio.

12. ATAX TUMIDUS WOLCOTT.

Atax tumidus Wolcott, 98; 285.

Very similar to A. (N.) ingens in form and in size, the females of both
showing a tendency to enormous distension when filled with eggs, in the
relative length of the legs, and also in color, the internal structure of each
as a rule giving no suggestion of the usual Y-shaped mark, but the color be-
ing a light brown with numerous fine white vermiculate lines, though speci-
mens of A. tumidus have been found showing quite a well defined Y-mark.
It was stated in the preliminary description of the species that it also
agreed in the manner of depositing eggs, but the possibility of an error
in this statement was changed to a probability by careful observations on
this point during the past summer.

The species is, under normal conditions, one of the lances of the
genus, the females measuring from 1.4 to 1.5 mm. in length and when
filled with eggs even 1.8 or 2.0 mm., the males ranging from 1.10 to 1.25
mm. The body is oval, broadened posteriorly, evenly rounded at both
ends and uniformly arched, being also highest posteriorly.

Eyes small, black, and separated from each other by a considerable
distance.

Maxillary shield similar to that of A. (N.) ingens, short and broad,

with no ancoral process produced posteriorly, and with muscles attached
to long curved processes projecting from the sides backward and upward.

NORTH AMERICAN SPECIES OF THE GENUS ATAX 237

Mandibles like those of A. arcuata and A. ypsilophorus with the line
separating the two portions carried backward on the ventral side toward
the base, thus causing the distal to encroach on the basal portion. But
here the encroachment is greater than in the other cases and the heavy
claw seems actually to spring from the side of the distal end of the basal
portion.

Palpi comparatively stout, segment 4 especially noteworthy in that
regard. The basal three segments are moderately thick but 4 is unusually
so, being through most of its length nearly as thick as 3, though narrowed
somewhat before the papillae on the ventral surface is reached and from
that point diminishing rapidly in diameter till at the tip it is only one-
half as thick as at the base. This segment is also short, being not twice as
long as 8 and its length only a little more than one-fifth greater than its
diameter toward its base. The paired papillae are very short while the
third at the tip is quite rudimentary. Last segment rather long, strongly
curved and blunt. Claws at the tip very small and inconspicuous.

Epimera resembling closely those of A. arcuata but relatively even
smaller.

Legs also resembling those of A. arcuata in general form but rela-
tively heavier and differing in the fact that I] is longer than III by about
one-tenth. The swollen body of the present species is also longer in pro-
portion to the length of the legs and only the last pair exceeds it in the
male, while in the female none equal it, [V being a trifle shorter. The
proportion between the segments resembles those in A. arcuwata, as re-
gards the relative length of 4 and 5 and the shortness of 6. The distal
segment is relatively stouter, and only slightly arcuate. The claws are
characteristic, being short and thick with two hooks, the ventral of which
is the heavier and somewhat the longer; it projects ventrally at a right
angle to the base of the claw and the dorsal hook after continuing for a
short distance in line with the base, also turns ventrad at a right angle.
The tip of the segment is expanded and has two flattened leaf-like spines
dorsally at the distal end which project beyond the claw.

Genital area.—Similar to that of A. arcuwata in general form but ab-
solutely larger and relatively broader; number of acetabula greater, in
the male 34 to 35, in the female 40 to 41. In the male they cover most of
the lateral plates which are reniform in shape, in the female while they
reach the inner margin posteriorly, they leave about one-half the width
bare anteriorly; two lying against the outer margin exceed the others in
size, as is the case in A. arcuata. ‘he inner margin of each plate is pro-
longed into a long, flat pointed spine of which the anterior margin is con-
vex, the posterior nearly straight, so that it is shaped something like a
beak. Its width at the base is equal to one-fourth the length of the inner
margin of the plate and it occupies the second fourth of the margin from
the anterior end. The genital plates are thick and the margins very
heavy, making a pronounced and ‘quite broad border.

238 ROBERT H. WOLCOTT:
MEASUREMENTS:

Male Female
Aenea Of MOY: iii: 55-)se lessee 1.170 mm. 1.660 mm.
luength ofjleg Toes. co seeiele 0.724 mm. 0.949 mm.
Lene thor, lee U5 evs Wie es beet t oe 0.994 mm, 1.372 mm.
Rength of leg Uae aoe oe os 0.938 mm. 1.255 mm.
engi otter TV ee eee acu 1.397 mm. 1.612 mm.
Length of palpus........... 2565) O.eBih warn, 0.372 mm.
Length of genital area......... 0.255 mm. -——-
Width of genital area.......... 0.821 mm. -_——- ——

Types in the author’s collection; co-types have been deposited in the
collection of the Zoological Laboratory, University of Nebraska, in the
Museum of Comparative Zoology of Harvard University, in the United
States National Museum, and in the Kgl. Museum ftir Naturkunde in
Berlin.

Atar tumidus was taken at Lake St. Clair in the summer of
1893, but only once, in Margaritana deltoides. At Ann
Arbor, Mich., three specimens were found in the collection of
the Zoological Department of the University of Michigan,
from the Huron River, but no record had been made of the
species of mussel. Two were collected at Lansing, Mich.,
but in what species of Unionide is uncertain.

It was only collected in North Michigan in Intermediate
Lake at Ellsworth, August 9, 1894, from Anodonta fragilis
and A. edentula—iZ specimens being secured.

At Grand Rapids, Mich., it has been collected in Anodonta
subcylindracea and Unio undulatus (once) from Grand River;
in Anodonta ovatz (?) from Plaster Creek; and in Anodonta
subcylindracea from the mill-pond at Mill Creek, near Grand
Rapids.

It thus has been taken only in Michigan and there but
rarely, yet seems generally distributed through the state; it
also seems to be restricted to Margaritana and Anodonta, and
has proven most abundant in A. subcylindracea.

13. ATAX (NAJADICOLA) INGENS (KOENIKE).

Atax ingens Koenike, 95b; 219, Pl. III, f. 65 to 67.

Najadicola ingens Piersig, 97; 60.

A. (N.) ingens is the largest of all our parasitic mites, especially if we
consider the size of the gravid females, one of which has been collected
measuring 6.0 mm., though the average length of the females is from 2.25
to 2.50 mm., and the males from 1.50 to 1.65 mm. The body is broadly
oval, evenly rounded at both ends, and much arched, highest posteriorly

NORTH AMERICAN SPECIES OF THE GENUS ATAX 239

When filled with ripe eggs the female resembles a large swollen sac, with
a cluster of short legs at one, and the more pointed end, which when the
mite is in a dish, are quite incapable of serving for support or locomotion
and the animal lies helplessly on. its back, unable to stir until some object
which it can grasp is brought within reach, when its attempts to right
itself and to escape from its uncomfortable situation are extremely
laborious and in eases of great distension of the body, even utterly vain.

It possesses a different style of coloring from all other species except
in the case of some specimens of A. tumidus, there being no Y-shaped
lighter mark upon the back, but the whole body being of a honey-yellow
color, deepening to a yellowish-brown on the back, with numerous and
irregularly distributed fine white vermiculate lines.

The eyes are reddish-brown, small and rather widely separated. The
maxillary shield is short and broad, and quite evenly rounded posteriorly,
though on either side of the median line at the posterior extremity there
is a small bulging of the outline due to a thickening of the margin of the
shield. On each postero-lateral margin a little behind the middle isa
curved chitinous process which runs laterally beneath the first epimeron.

The mandible is long and slender with an extreme breadth of a little
over one-fifth the total length, It is thin and delicate, especially at the
ventro-posterior angle where it is produced backward to a distance equal
to one third the total length, forming a rectangular plate which is hol-
lowed, producing a shallow mandibular furrow. The diameter of the
basal joint is greatest just anterior to the posterior dorsal angle and
grows gradually less till at the junction of the distal joint it is only about
half as great. The distal joint is relatively small, with a claw which is
broad, curved, indistinctly angled near the base, and sharply pointed. At
the dorsal side of this claw is a thin flattened tapering chitinous process.

The palpi are moderately heavy and relatively short, averaging only
about one-third the length of the body. The first segment is unusually
long and much broader at its basal than at its distal end, which is not
true of 2, the distal margin of which is twice the breadth of the basal.
The ventral margin of 2 is straight, the dorsal moderately convex; on the
inner side are four spines, one near the middle at the dorsal side,a second
a short distance ventrad and posteriad of this, and two others distad of
the second, forming with it a row running to the middle of the distal
margin. On the outer side of this segment a little proximad of the middle
and toward the dorsal side are five small spines, enclosing an area which
is a nearly regular pentagon. 3 is stout, its ventral margin nearly
straight and more than half the slightly convex dorsal margin, and with
asmall spine on the inner side near the proximal margin. 4 is rather
clumsy, nearly as thick at the distal as at the basal end, and bears two
very inconspicuous papillae near the distal margin, and a small spur at
the margin, on the ventral side. There is also a short, thick, blade-like
spine on the inner side at the distal margin, and 5 has the usual three
claws at the blunt tip. The palpi thus possess the general characters of
those of other species of Ataw, being peculiar in the number of spines on
2 and the one on the inner surface of 4.

A a ee

QAO ROBERT H. WOLCOTT:

The epimera cover only about one-third the whole ventral surface.
The two groups of each side leave but a narrow interval between them,
but the space between those of opposite sides is wider, especially in the
case of the anterior pair. The epimera of the male are relatively larger
and closer together than in the female. J and II form a roughly triangu-
lar plate with a rounded inner angle, and from the inner end of the pos-
terior margin of II a short, stout, curved process runs back beneath III. ~
Of the plate formed by III and IV, III furnishes about one-third. This
plate is longest externally, narrowed toward the median line and the
inner end is rounded. All epimera are relatively thick.

Legs relatively short and stout, and the first pair slightly heavier
than the rest. In females not distended with eggs and in males the first
leg is a little over one-half the body length, II is a little longer than I, II
is longer still and over three-fifths the length of the body, and IV is longest
but still less than the body-length. The proportions seem to be about the
same in the two sexes. Of the individual segments, 5 is in all legs the
longest, 6 about equal to it except in IV where 5 is slightly lengthened,
and 4 next in length. The distal segments are nearly as thick as the
proximal which gives the legs a rather clumsy appearance. Spines are
comparatively very few and all short and stout; aside from this they are
peculiar only in the fact that each segment except 1 and 6, bears at the
distal end, a group of from four to six of these short, stout spines. The
claw is received in the end of 6 in a manner similar to that found
in A. ypsilophorus and the distal end of the segment is slightly expanded.
The claw is long, slender, strongly curved and slightly angled at two-
thirds the distance from the base, in the case of all but the first leg. In
the case of I, the claw is stouter, shorter and evenly curved, but like all
the rest simple and sharply pointed.

Genital area not at the end of the body but close behind the last
epimera and so produced toward either side that the total breadth is
about the same as the distance between the outer margins of the posterior
groups of epimera, and approximately two-thirds the width of the body.
Each plate has an outline roughly that of a right-angled triangle, the base
of which corresponds to the anterior margin, the hypotenuse to the pos-
terior margin, while the short inner margin represents the altitude. The
latter margin lies at a short distance from the genital cleft in the female,
but in the male bounds it, and meeting the plate of the opposite side in
front and behind, surrounds it. The anterior margin is nearly straight,
the posterior slightly convex and the outer end rounded. The acetabula
are numerous and vary in size, two toward the outer end of each plate
being larger than any of the rest.

MEASUREMENTS:
Male Female
MSW NLOL OGY Misti Oe eis cis ote dS poe 1.503 mm. 2.330 mm.
LL STT/-CAU TE CONST CRE VA a PN 0.826 mm. 1.264 mm.
BemettyOIMer UL jis ex seo sls veces as 0.862 mm. 1.346 mm.
menmthioriles TED Fae ey. hs es 0.943 mm. 1.581 mm.
MenpuhvotilesitVii( 2) 8.5) dard) Se aie ete 1.367 mm. 2.017 mm.

Hen ephyOLpPAalpUss. 625% sh cise doen 0.469 mm. 0.821 mm.

NORTH AMERICAN SPECIES OF THE GENUS ATAX QAI

This species was first identified from a specimen collected at
<< 96” Lake, near Charlevoix, Mich., from Anodonta fragilis,
and another collected at Intermediate Lake, Ellsworth, Mich.,
also from A. fragilis. Koenike described it from that species
and from Unio complanatus.

It seems to be found in both Unio and Anodonta, as at
Grand Rapids, Mich., it has been collected in Unio gibbosus,
U. ligamentinus and Anodonta footiana. In one specimen of
A. footiana were 23 irregular masses of eggs, varying from
1.0 to 2.5 mm. in diameter, and in various stages of develop-
ment, with one mite 2.0 mm. long and another, afemale full of
eggs, 6.0 mm. inlength. At Long Lake, Kalamazoo, Mich.,
one male has been taken from U. luteolus. Only 16 speci-
mens have been found altogether, so it seems, like A. twmidus,
to be a rare species.

SYNOPSIS OF THE SPECIES INCLUDED ABOVE.

1. Genital field toward the end of the body and
in general form more or less broadly oval
or approximately circular; females with va-
riously modified spines about the genital
opening which assist in oviposition, the

eggs being Cee singly in the aoe
(ATAX)... ‘ Bede ory ecu) INA
Ganital rei ecowaals ‘eee Nie
end of the body, immediately behind the
last epimera and plates so extended trans-
versely as to have the form of very low
broad triangles, whose long bases extend
from either side of the genital cleft a con-
siderable part of the way toward the side
of the body. No spines at genital opening,
the eggs being laid in masses between the

gills (Nasapicona)........ 18 A. (V.) éngens (Koen.)
2. Acetabula 6 on each side in two groups of
IDNR CG) TV EE ek A ea 2

16

242

ROBERT H. WOLCOTT:

Acetabula 5 on each side. ..2. 0.665. .. ee
Acetabula more than 6 on each side............ 10.

First pair of legs thicker than the palpi,
with movable spines set into the sides of
deeply excavated conical papillae, and with
claws simply bifid.......... 1. A. crassepes (Miull.)
First pair of legs not so thick as palpi, with-
out movable spines, and with a broadly ex-
panded pectinate claw...... 2. A. pectenatus mihi.
Legs very long, first pair thicker than palpi;
body truncate posteriorly and with a promi-
nent nipple-like papilla at either lateral
posterior angle............ 3. A. aculeatus Koen.
Legs shorter and first pair not so thick as

palpi; body evenly rounded or emarginate

behind. 3... lens em Stas oe 208 «er
Last pair of legs modified and posterior mar-
gin of the body emarginate...... 2
Last pair of legs not modified and posterior
margin of the body rounded.....2. 2%...

Modification consisting of a curved fourth
segment on last pair of legs. Legs long
and slender....... 4. A. intermedius Koen., male.
Modification consisting of a thickening of
the first four segments of the last pair of
legs, and a shortening of the fifth, which
bears two heavy spines, while the sixth is
long and slender. All legs stouter and
thicker............. 5. A. abmormepes mahi, male:
Genital plate of each side divided into two
parts, with two and three acetabula re-

spectively. . ae ol
Genital pate 0 on fenels ian ee distill the
vided . sesye de Meee «9 ote alee

Claw with two hao heute sight in onisthy
4. A. intermedius Koen., female.

10.

it:

12.

13.

NORTH AMERICAN SPECIES OF THE GENUS ATAX 943

Claw with a very small accessory tip on the
convex side of the principal one.
x ES EAD, abriorvwipe rahi female.
Tash two See tents placed side by side; claws
bifid . Dero rail 0 90) Sul Ak Fossulatus’ Koen.
neues paced i in a continuous line; claws
simple ee Awa ees Pai se hea TL aa.) Aah Sameera TOE.
Weethaate about nine on each side. Hind
leg of male modified...... 6. A. indistinctus mihi.
Acetabula’20/or more on each side... 63.0. -.)05 °° 21.
Distal segment of palpus expanded, quad-
rate and with two long curved claws.
Body slightly emarginate in male, and legs,
especially of females, with more or less ser-
rate spines. Lie a Sale ahaa Lh) segprandis DOveeL.
Distal scone of pales slender, curved
and ending in a blunt point armed with
small claw-like spines. Body not emargi-
nate behind and no serrate spines on the legs. 12.
First pair of legs not noticeably thicker than
the rest; distal segment of the legs straight,
and claws large and with two long equal
hooks: (27) eo Se LL) AY gpsilophorus (Boz).
First pair of legs noticeably thicker than the
rest and tapering from base to tip; distal
segment slender, more or less arcuate and
claws small and bifid. ee as, a eM ae RED
Distal segment of lees iaeetioule ahioiena)
fourth segment of palpus tapering from base
to apex. Maxillary shield with an ancoral
process posteriorly.......... 10. A. arcuata mihi.
Distal segment of legs slightly arcuate;
fourth segment of palpus swollen and nearly
uniform in diameter from the base to the
paired papillae on the ventral surface. Max-
illary shield with no ancoral process poste-
riorly.. PRA WR eid De A demas to:

944 ROBERT H. WOLCOTT:

BIOLOGICAL CONSIDERATIONS.

Most of these mites pass all their life stages within the
limits of the mussel’s shell, moving about over the surface of
the mantle; a few, of which A. crassipes is an example, remain
only till the last stages of development are reached and then
leave the shelter of the mussel to pass the remainder of their
life swimming freely about in the water. The eggs are depos-
ited singly in the mantle and gills, rarely, as in A. (1V.) mgens,
in masses between the gills. The spines guarding the genital
opening, by being inserted into the surface of the gill, prob-
ably assist in oviposition, either by holding the body firmly
against the surface of the gill or mantle which is then pierced
by the ovipositor, or by themselves piercing the surface, the
ovipositor being protruded between them and the eggs de-
posited, rather more abundantly in the gills apparently, in the
ease of the Unio-dwellers, more numerously in the mantle by
the Anodonta-parasites. The development of these eggs has
been studied by Ciaparéde (68) and others and five stages hi
been distinguished.

First, the egg stage, in which the embryo is surrounded by
a firm outer membrane and a more delicate inner membrane
—the ‘‘ Zwischenhaut ”’ of Claparéde (68), the ‘‘ Dotterhaut ”’
of Kramer (80) or the ‘‘Apoderm” of Henking (82). The
former, as development proceeds and the embryo increases in
size, is ruptured, but the latter increases in size or is capable
of distension and remains surrounding the embryo till the young
mite is ready to emerge, when it is also burst open and the larva
appears. Third, the first larval stage, in which the mite has but
three pairs of legs, and whichis very short. Fourth, the nymph
stage, in which the larval legs are lost and a new set is de-
veloped beneath the old larval skin. Fifth, the second larval
or sub-imago stage, in which the mite has four pairs of legs but
in which it lacks still the perfect development of the sexual ap-
paratus and the relative proportions belonging to the adult,
those only being acquired when a final moult of the skin re-
veals the adult mite. It is not the intention in this paper to
go into details as to this process, further than to note that the

NORTH AMERICAN SPECIES OF THE GENUS ATAX Y45

first two stages are passed in the substance of the gill, and the
next apparently in the spaces between the plates of which the gill
is composed. This stage is very short and the nymph is soon
formed either in the spaces in the gills or outside them in the
mucous over their surfaces. In the latter case the nymphs ac-
cumulate in the mass of mucous at the exhalent aperature, and
the same species of mite has been reared both from nymphs
taken from the gills and from those collected in the latter situ-
ation. During the second larval stage the mite is very active
and moves freely about between mantle and gills. Generation
follows generation in the mussel, the only check to the increase
in number of mites being afforded by accidental escape or
voluntary migration. The latter, as Kramer (91) observes,
usually occurs during the second larval period when the body
is smaller, the legs longer, and the mites more active than
later. When free from the ancestral mussel they no doubt
swim here and there or clamber over the bottom with a chance
of finding another mussel and effecting a lodgment therein.
However, collections made with nets over beds of mussels have
never, so far as the anthor’s experience goes, furnished speci-
mens of these migrating mites.

There seems to be no particular time of year when eggs are
deposited as they are found throughout the season, but are ap-
parently most numerous in the summer, while during early au-
tumn the adult mites are most abundant. There also seems to
be no one time at which the eggs from any one female mite are
laid, but in the same shell and with but a single female, and in
which other conditions lead to the inference that she laid all
the eggs, they are found in various stages of development.

Lodgment is effected probably with different degrees of fa-
cility in different species of mussels. The swiftness of the cur-
rent seems to have little effect in preventing it, if indeed it
does not assist. In lakes with practically no current, collec-
tions show the following percentage of those infested, no other
conditions being regarded, and all collections being made
during August of different years:

9A ROBERT H. WOLCOTT:

- In Lake St. Clair (Anchor Bay), of 251 mussels, 62 pe
cent infested.

In Intermediate L., N. Mich., of 52 mussels, 65 per cent
infested.

In Reed’s Lake, Grand Rapids, Mich., of 96 mussels, 64.5
per cent infested.

While in Grand River, with a rapid current, collections at
various points show:

Of 175 mussels, 62.33 per cent infested;
Of 73 mussels, 60.00 per cent infested;
Of 182 mussels, 90.50 per cent infested;
Of 85 mussels, 82.00 per cent infested.

These last two larger percentages were obtained during the
past summer, when the percentage of infested mussels was un-
. usually high. Indeed careful observations made during the
summer in the attempt to secure more accurate data than had
heretofore been obtained, as to the effect of different conditions,
were rendered practically of no value from the fact that the
percentage of mussels infested was so abnormally high as com-
pared with other seasons that no accurate comparison could be
made with former years and other localities. Still further ob-
servations are necessary and only general statements can be
made in the discussion which follows.

The mussels which are most sensitive, most active in closing
their shells, and whose shells close most tightly, seem to be
more immune from the presence of parasites than those possess-
ing less of these properties. The following figures have (p. 245)
been selected with reference to such species of mussels as have
been represented in the collections by a considerable number of
specimens and illustrate different types as regards form.

If these U. occidens and U. ventricosus are thick, the valves
meet at a considerable angle and not closely, and they are
slower to close upon irritation. U. gibbosus, U. rectus and
U. nasutus are long and thin, the valves meet at a small angle
and tightly and they are more active. The other forms are in-
termediate in these respects.

NORTH AMERICAN SPECIES OF THE GENUS ATAX¥ “ O47

Collected Collected
Mussel. previous to Per cent during Per cent
1898. infested. 1898. infested.

Unio ocerdens 16) AOAOUOD > 40° & 400,00
Unio ventricosus
Unio luteolus 60 70.00 33 85.00
Unio ligamentinus 57 63.00 75 96.00
Unio plicatus
Unio undulatus He eH a eel
OE 46° 15.00 36 55.00
Unio rectus
Unio nasutus 94 4.00 sea 5 SALA oe

This past summer, however, in the case of U7. spatulatus
and U. Novwi-eboract, which are very similar in size and form,
an apparent exception to the rule was found; for of 46 speci-
mens of U. spatulatus, 20, or 43 per cent. were parasitized,
while of 24 of the other species collected with U. spatulatus,
all were infested. JU. .spatulatus has, to be sure, the ad_
vantage in the angle at which the shells close and in activity,
but hardly sufficient to lead one to infer the ahove result from
simply a comparison of those characters. The mussels repre-
sented in the above table were all from Michigan, none from
elsewhere being included, in order to avoid any necessity of
allowing for a difference of locality. All were collected to-
gether along the Grand River at Grand Rapids, except U.
nasutus which was from Lake St. Clair and U. luteolus which
represented specimens from Lake St. Clair, Reed’s Lake at
Grand Rapids, and White Lake, Muskegon County, together
with a few from North Michigan Lakes. Comparison of JU.
luteolus from the different localities showed practically a uni-
form percentage.

As between Anodontas and Unios, of 29 Anodontas taken
previous to this year at the same localities as the above men-
tioned Unios, omitting U. luteolus, 17 or 58.5 per cent were
infested; of those taken this summer 68 out of 74 or 72 per
cent were infested. Anodontas taken with the JU. luteolus
enumerated above, previous to 1898, showed a percentage of
72 per cent or 33 out of 46, and during 1898, of 95.5 per cent
or 21 out of 22.

YA8 ROBERT H. WOLCOTT:

The size of the mussel seems to have little effect. No
accurate records were made in regard to this fact previous to
the past summer and for reasons stated above, these records
are of little value in proving or disproving the fact of any
connection between size and percentage of mussels infested.
Generalizing from experience, in the absence of previous ac-
curately recorded observations, it seems, however, that there
is none.

The same is true of sex, which seems to affect inno degree the
extent of parasitism, though it might be supposed that especially
in the case of a gravid female entrance by the mite might be
the more easily effected.

Records kept the past summer also as to depths at which the
shell was buried and amount of vegetation on the bottom,
furnish no satisfactory data. It has become evident that it is
not an easy matter to collect facts in such form as to allow of
a proper comparison of the importance of the various factors
which determine the occurrence of parasitic mites in various
species of Unionidae and under different conditions. And: it
has also become evident that perfectly accurate statements,
with the accumulation of the data necessary to furnish an
adequate basis for them, will only be possible after years of
careful observation. The author regrets that he has not the
benefit of such in the preparation of this paper, but hopes that
he may at some time in the not far distant future be able to
report more fully upon this exceedingly interesting subject of
research.

The maximum number of mites found ina single shell has
occurred in the case of an Anodonta plana from a pool near
Lincoln, Neb., opened in September,1895. In it were 15 Ataw
ypsilophorus and 406 A. intermedius—93 males and 3138
females. The mussels collected in Nebraska, however, espec-
ially the Anodontas, have averaged more mites to the specimen
than those collected in Michigan, though the percentage of
those infested is about the same.

The presence of these mites seems to entail few, if any, con-
sequences upon the host; though Garner (64) claims that their

NORTH AMERICAN SPECIES OF THE GENUS ATAX 249

presence causes the growth of pearly prominences on the inside
of the shell, and it is possible the irritation due to the presence
of eggs in the mantle, might in some cases lead to this. The
figures collected the past summer are not sufficient to allow of
accurate statements being made. When the attempt is made to
allow for the effect of age, of variation in form in the different
species, and situation as affecting the probability of the en-
trance of foreign particles, the number of mussels examined
does not furnish sufficient data for definite conclusions. Other
sources of uncertainty are added when it is considered that
even if no mites are found in a mussel of considerable size the
assumption that it never has contained any is entirely unwar-
ranted, and when it is remembered that in case of infested
mussels we have no means of knowing how long the mites have
been there and whether or not sufficient time has elapsed for
the demonstration of any effects on the host.

But upon the mites themselves the effect is more pronounced.
Living in the gills during development and later in a slimy
secretion, as they do, the tracheal system is less perfectly
developed, in some cases becoming quite rudimentary. Yet
they live for weeks in a vessel of water after removal from
the mussel. Here the other effects of parasitism become
apparent, especially if we compare free-living and parasitic
species. The body of the parasitic forms is large and more or
less unwieldy, in the case of the females of A. twmidus and
A. (lV.) ingens so large, at times, as to incapacitate the mites
for any movement, and the great thing lies on its back kicking
its legs in the air utterly unable to even hold itself right side
up. The swimming powers are feeble and the animal sinks at
once to the bottom where it clambers clumsily about, fortunate
if any soft object allows it to obtain a foothold, at a great dis-
advantage if it be on a bottom too hard to allow its claws to
penetrate. An apparent immunity from this effect of parasit-
ism is seen in the case of A. aculeatus which, living as it does
along the edge of the mantle and about the exhalent aperature,
is more exposed to currents of water and retains the length of
legs, small size of body and activity of movement almost un-

950 ROBERT H. WOLCOTT:

impaired—indeed, it is quite as good a swimmer as A. crassipes.
Aside from increase in size and unwieldiness of form, there is
a lack of the bright coloring which makes the whole group such
interesting objects of study. The method of oviposition leads
finally to peculiarities of structure in connection with the
female sexual organs, consisting of the spines about the genital
opening previously referred to. If kept for some time in a
vessel of water cannibalism is never resorted to, no food is
taken, and after weeks of starvation the mites finally die.
Haldeman (42) says they do not suffer from cold, as they are
pretty active in water a few degrees above the freezing point;
and he has found them moving about in a Unio, the outside
layer of which was frozen. Nevertheless, they become torpid
instantly, he says, if placed in freezing water, though the tor-
pidity remains but a short time, if the temperature be gradually
raised. As arule, the migrations of the mussel from shallow
to deep water and its habit of burying itself in mud during the
winter, must make the temperature conditions within the shell

very constant. Equally uniform is the supply of food, which
is furnished to the animal with a minimum amount of exertion.

This stability of conditions under which the animal lives
would lead us to expect little variation among the mites and
little is found. Cases occur, involving the number, size, form,
etc., of acetabula on the genital plates, and to a slight degree

the relative dimensions and characters of other parts. But in
no case are these sufficient to cause any confusion amongst
different species, even when these are found living together in
the same mussel. Specific characters are well defined and con-
stant, and with care in the examination of specimens and a
knowledge of the characteristic structural features of each
species, identification should be perfectly sure.

The strange thing is that under conditions so stable, so
many species should occur. In this respect as compared with
the European fauna ours seems remarkably rich, since we have
now 13 recorded species of Atax as compared with 8 from all
parts of the continent of Europe, and our list is likely to be
increased by collections in the more distant parts of the coun-

NORTH AMERICAN SPECIES OF THE GENUS ATAX 2Q51

try, although those so far made cover seven states, from New
York and Pennsylvania to Nebraska, and represent, all told,
forty-one localities—2 in New York, 4 in Pennsylvania, 21 in
Michigan, 1 in Wisconsin, 4 in Illinois, 2 in Iowa, and 7 in
Nebraska. Material would be especially valuable from the
South and from the Pacific Coast, and it is hoped this paper
may be an incentive to investigators to take up the work of
collecting Hydrachnide from those regions. Any material
sent to the writer will be gratefully acknowledged, and if de-
sired, labelled specimens returned; he will also gladly respond
to any requests for information concerning the group.

Finally, the author would be doing an injustice both to those
who have very generously assisted him and to his own senti-
ments of grateful appreciation, did he fail to acknowledge that
assistance. To Dr. Richard Piersig of Leipzig, Germany, and
to Prof. F. Koenike of Bremen, he is indebted for literature,
and to Prof. Koenike also for specimens; each has been very
generous and to the kindness of each he acknowledges his in-
debtedness. Material has been received from Mr. R. A.
Johnson of Harvard University, Dr. R. H. Ward of Troy, N.
Y., Mr. Jas. B. Shearer of Bay City, Mich., Mr. M. Ricker
of Burlington, Ia., Prof. H. M. Kelly of Cornell College, Ia.,
Mr. O. D. Noble of Linwood, Neb., and Prof. H. B. Ward
of the University of Nebraska, to each of whom the author ex-
tends his grateful acknowledgments. To Prof. Ward and to
his former teacher, Prof. J. E. Reighard of the University of
Michigan, he extends his thanks for many personal favors, and
he also acknowledges his obligation to Mr. Bryant Walker of
Detroit, Mich., for assistance in the identification of the mus-
sels collected. Finally, it is just and proper that he acknowl-
edge the assistance of his wife in the routine of the examina-
tion of mussels collected. He shall feel that he has partially
repaid his obligations to those mentioned if that which he
has accomplished by their assistance shall meet with their
approval.

252 ROBERT H. WOLCOTT:

BIBLIOGRAPHY.

Von BAER, CARL ERNST.
27. Beitrage zur Kenntniss der neideren Thiere. Nova Acta
phys-med. Acad. Caes. Leop.-Carolinae nat. cur., xiii, pt. 2, 523—
762. Bonnae, 1827.
Describes A. ypsilophorus as Hydrachna concharum.

BARROIS AND MONIEZ.
87. Catalogue des Hydrachnides recueillies dans le nord de la
France. Lille, 1887. 36 pp.
A. crassipes (Miill.), Cochleophorus spinipes (Miill.), C. vernalis
(Miill.), A. ypsilophorus (Bonz), A. Bonzi (Clap.).

VAN BENEDEN, P.J.
48. Recherches sur, l’histoire naturelle et le développerenl de I’
Atax ypsilophora (Hydrachna concharum), etc. Bruxelles, 1848.
(24 pp., 1 pl.).
The species studied was A. intermedius Koenike.
BERLESE, ANT.
82. Acari, Myriopoda et Scorpiones hucusque in Italia reperta.
79 Fascicles and supplement. Padova, 1882—’96.
A. crassipes and ‘‘A. limosus Koch’’ (according to Piersig (96b),
A. limosus Koch = Cochleophorus spinipes (Mill.).

BESSELS, EmMIt.

69. Bemerkungen iiber die in unseren Najaden schmarotzender
Atax-Arten. Jahreshft. d. Ver. vaterl. Naturk. Wiirtt. xxv, 1869,
146-152. Transl. by W.S. Dallas in Ann. and Mag. Nat. Hist.
vii, 1871, 55-59.

Observations on development, ete.

BONZ,CHRISTOPH. GOTTLIEB.
1783. Nova acta phys.-med. Acad. Caes. Leop.-Carolinae nat. cur.,
etc. Observatio x. vii, 52-53, Pl. I, f. 1--4. Non ae 1783.
Describes Acarus ypsilophorus.

BRuZELIUS, RAGNAR MAGNUS.
64. Beskrifning 6fver Hydrachniden, som forekomma inom Skane.
Akad. Abhand]. Lund, 1854.
Restricted the genus to the limits since recognized; includes in ob-
servations A. crassipes and Coch. spinipes.

Nore.—In this bibliography no mention has been made of articles
which are simply records of occurrence. The different references are in-
dicated by date, together with letter following when necessary. The
designation given to each reference corresponds to that in the card cat-
alogue of the author. which is believed to be complete, aud in which the
sequence adopted is carefully chosen to indicate the order of publication.
This designation is here retained to preserve a uniformity of citation in
this and other papers.

NORTH AMERICAN SPECIES OF THE GENUS ATAX 253

CLAPAREDE, EDOUARD.
68. Studien an Acariden. Zeitschr: fir wiss. Zool., xviii, pt. 4,
1868, 446--480.
Describes fully the development of A. ypsilophorus; describes A.
Bonzi.

Dapay, Eve. V.
97. Die Fauna des Balatonsees. x. Wassermilben (Hydrachniden),.
Result wiss. Erforsch. Balatonsees ii, pt. 1, 195--205.
Describes Atax Hungaricus,=Cochleophorus spinipes (Miill.),juv.
98. Mikroskopische Stisswasserthiere aus Ceylon. Termézetr.
Fiizeter.,xxi, 1898, 123 pp., 55 text figures.
Describes Atax nodosus and A. singalensis, of which A.
nodosus belongs to Cochleophorus.
Dana, (JAs. D.) AND WHELPLEY (JAS.).
36. On two American Species of the genus Hydrachna. Silliman’s
Amer. Jour. Sci. xxx, 1836, 354--359. Plate.
Describes Hydrachna formosa (= A. ypsilophorus) and H. pyri-
formis (spec. undet.).
Dues, ALF.
84. Naturaleza México, vi, 344.
Atax Alzatei, n. sp. (is a Curvipes).
DuGEs, ANTOINE.
34. Recherches sur l’ordre des Acariens. Deuexiéme Memoire. Re-
marques sur la famille des Hydracnés. Ann. Sci. Nat. 2me Série
i, Zool., 1834, 144-174, Pl. x, xi.
Restricted genus Atax by separation of Diplodontus and Arren-
urus, but as types of Atax gives Hydrachna histrionica Herm. (a
Limnesia) and H. lutescens Herm. (a Piona).

FABRICIUS, JOH. CHR.
1792. Entomologia Systematica, ete. Hafniae, 1792-1794, 4 vols.
In vol. ii, pp. 398-406, gives all of Miiller’s species but H. gros-
stipes, under the genus Trombidium.
05. Systema Antliatorum, etc. Brunsvigae, 1805.
Establishes genus Ataxw (= Hydrachna, Miiller).
GARNER, R,
64. Ona Parasitical Acarus of theAnodon. Rept. 33d Meet. Brit.
Ass. Ady. Sci. Notices, 114.
A. ypsilophorus causes growth of pearly prominences on inside

of shell.
GIROD, PAUL.
89. Recherches anatomiques sur les Hydrachnides parasites de

l’Anodonte et de l’Unio, Atax ypsilophorus et Atax Bonzi. Bull.
Soc. Zool. France, xiv, 1889, 107-110. Jour. Roy. Mic. Soc. Lond.,
1889, 746-747 (abstract).

93. Recherches sur la respiration des Hydrachnides parasites.
Assoc. frang. Avance. Sc. 22 Sess. Besancon, pt. 1, 248.

954 ROBERT H. WOLCOTT:

HALDEMAN, S. S.
42. On some American species of Hydrachnidae. Zoological Con-
tributions, No. 1. Philadelphia, 1842.
Describes 9 spp. of mussel parasites under the ‘Genus ?
Unionicola’’—U. oviformis, U. lactea (both = A. ypsilophorus),
U. personata, U. humerosa, U. symmetrica, U. proxima, U. lug-
bris, U. unicolor, U. reticulata (spp. undet.).

HALLER, G.
81a. Die Hydrachniden der Schweiz. Mitth. der naturforsch. Ges-
in Bern. ii, 1881, 18-83, Pls. i-iv. Separate, Bern, 1882.
Synonymy and notes on A. ecrassipes, A. ypsilophorus, Coch.
spinipes.
HARRINGTON, FLETCHER AND TYRRELL. ;
84. Report of the Entomological Branch for the season of 1883.
Ottawa Field Naturalists’ Club, ii, 1884, 184-140.
Atax Bonzi (incorrect identification?) and A. ypsilophorus in
America.

HENKING, H.

82. Beitrige zur Anatomie, Entwicklungsgeshichte und Biologie
von Trombidium fuliginosum Herm. Zeit. f. wiss. zool, xxxvii,
1882, 553-663, Pls. xxxiv—xxxvVi.

IHERING, H. Von.

92. On the Geographical Distribution of Atax. Tr. N. Zealand

Inst., xxv, 252-253.
Kocg, C. L.

380. Deutschlands Crustaceen, Myriapoden und Arachniden. Regens-
burg, 1835-41 (40 parts). Also in Panzer’s ‘‘Deutschlands
Insekten,’’ beginning with part 132.

37. Uebersicht des Arachnidensystems. Niirnberg, 1837-43
(4 parts).

In the former, simply describes species, in the latter arranges
them systematically. Restricts Afaw by separating from it the
genera Nesaea, Piona, Hygrobates, Hydrochoreutes, Atractides,
Acercus, Maricaand Limnesia. Describes under Atax, A. cras-
stipes (Miill.); A. truncatus, albidus, truncatellus, confluens,
elegans (all= A. ecrassipes (Miill.)—Piersig, 96b); A. figuralis,
diaphanus, lobatus (all= A. figuralis Koch-Piersig, 96b); A.
spinipes (Mill.), freniger, falcatus, limosus, fastuosus, pictus,
hyalinus, bifasciatus, furcula (all = Coch. spinipes (Miill.)—
Piersig, 96b); A. vernalis (Miill.) (Cochleophorus); A. grossipes
(Miill.) (ident. 7) A. minimus Koch (ident. 7).

KOENIKE, F.

81a. Revision von H. Lebert’s Hydrachniden des Genfer Sees.

Zeitschr. f. wiss. Zool., xxxv, pt. 4, 1881, 613-628.

8ib. WVorlaufige Notiz tiber die Bedeutung der ‘‘Steissdriisen”’ bei
Atax crassipes (Miill.). Zool. Anz. iv, 1881, 356-357.

82.

90.

90a.

90b.

91.

91c.

93.

93c.

95.

95a.

95b.

NORTH AMERICAN SPECIES OF THE GENUS ATAX 255

Ueber das Hydrachniden Genus Atax. Abh. naturw. Ver.
Bremen, vii, 1882, 265-268.

Ein neuer Bivalven-Parasit. Zool. Anz. xiii, 1890, 138-140.
A. aculeatus, n. sp. from Germany.

Eine Wassermilbe als Schneckenschmarotzer. Zool. Anz, xiii,
1890, 364-365.
A. Ampullariae, n. sp. from §. Brazil.

Siidamericanische auf Muschelthiere Schmarotzende Atax-
Species. Zool. Anz, xiii, 1890, 424-427.
A. procurvipes, n. sp., A. perforatus, n. sp., A, rugosus, n. sp.,
A. Jheringi, n. sp. from S. Brazil.

Noch ein Siidamericanischer Muschel-Atax. Zool. Anz. xiv,
1891, 15-16.
A. fissipes, n. sp. from S. Brazil.

Kurzer Bericht itber Nordamerikanische Hydrachniden. Zool.
Anz., xiv, 1891, pp. 256-258.

Die von Herrn Dr. F. Stuhlmann in Ostafrica gesammelten
Hydrachniden des Hamburger naturhistorischen Museum. Jahrb.
wiss. Anst. Hamburg, x, 1893, 1-55, 3 Pls. Also separate.
Describes A. spinifer, n. sp., A. simulans, n. sp., (both Cochleo-
phorus).

Weitere Anmerkungen zu Piersig’s Beitragen zur Hydrach-
nidenkunde. Zool. Anz., xvi, 1893, 460-464.
A. triangularis Piersig not valid—name preoccupied by Say,
1821.

Hydrachniden. Aus; Deutsch-Ost-Africa. Vol. iv, Die Thierwelt
Ost-Africas, Wirbellose Thiere. Berlin, Geog. Verlagshdlg.
Dietr. Reimer, 1895. 18 pp.

A. spinifer Koen., A. simulans Koen., A. spinipes (Miill.), A.
pauciporus, n. sp., A. lynceus, n. sp., A. figuralis Koch (figs.
only) (all Cochleophorus but the last two).

Liste des Hydrachnides recueillies par la Dr. Théod. Barrois
en Palestine, en“Syrie et en Egypte. Rev. Biol. Nord. Fr., vii,
1895, 139-147. Separate, Lille, 1895.

A. crassipes from Palestine.

Nordamerikanische Hydrachniden. Abh. des naturwiss. Ver,
zu Bremen, xiii, 1895, 167-226. Pls. i-iii. Also separate.

A. ypsilophorus (Bonz), C. vernalis (Miill.), A. ingens, n. sp., A.
fossulatus n. sp., figs. of A. procwrvipes Koen.

95d. Ueber bekannte und neue Wassermilben. Zool. Anz., xviii,

1895, 373-386, 389-392. 17 figs.

A. tricuspis, n. sp., (Germany), A. Schmackeri, n. sp. (China), A.
verrucosus, n. sp. (Germany) (Cochleophorus), A. callosus, n. sp.
(Germany) (also a Cochleophorus).

956 ROBERT H. WOLCOTT:

96. Holtseinische Hydrachniden. Forschungsber. aus der Biol.
Station zu Plon., iv, 1896, 207-248. Pl.
A. crassipes (Mall.), A. limosus (Koch) Berlese, C. spinipes,
(Mill), C. vernalis (Miill.), A. ypsilophorus (Bonz), A. interme-
dius Koen.

KRAMER, P.

75. Beitrage zur Naturgeschichte der Hydrachniden. Arch. f.
Naturgesch, xli, 1875, 263-882.
Describes 4. coeruleus and A. loricatus, both of which = Coch.
spinipes.

77. Grundziige zur Systematik der Milben. Arch. f. Naturgesch.,

xliii, 1877, 215-247.
Systematic.
80. Ueber die postembryonale Entwicklung bei der Milbengattung
Glyciphagus. Arch. f. Naturgesch., xlvi, 1880, 103-110.
Krenpowsky, M. E.

78. [Ueber die Erscheinung der Metamorphose bei Wassermieben].
(Russian). [Arbeiten der naturf. Ges. Charkow]. 66 pp. 2 pls.
On metamorphosis, Refers to 4. coeruleus Kram. (Cochl. spin-
ipes.)

[Les Acariens d’eau douce (Hydrachnides) de la Russie merid-
ionale]. (Russian). [Arb. Naturf. Ges. Charkow]. xviii, 1885.
209-358. 2 pls.

A. crassipes Miill., A. coeruleus Kram., (Coch. spinipes), A. ypsi-
lophorus, v. Ben. (A. intermedius Koen.), A. corcharum v. Baer
(A. ypsilophorus (Bonz), ‘‘A. Bonzi v. Ben.”’
LABOULBENE, ALEX.
51. Description de quelque Acariens et d’une Hydrachne. Ann.
Soc. Ent. France, 2 me série, ix, 1857.
His Hydrachna (Atax) viridana, according to Neuman (79) be-
longs to Arrenurus.
LAMPERT, KARL.
93. Parasiten der Teichmuschel (Anodonta mutabilis Cless).
Jahresheft Ver. vaterl. Naturk. Wiirtt. 1, 1893, 79-80.
A. intermedius Koen.
LEBERT, H.
79. Matériaux pour servir a |’étude de la faune profonde du lac

io 2)
ct

’

Léman, par Dr. F. A. Forel. vi Série. Hydrachnides du Léman..

Bull. Soc. Vaud. Sc. Natur., xvi, 1879, 327-377, 2 pls.
Refers to 4. ypsilophorus, A. crassipes, and under ‘“‘new genus,
Neumania’’, describes N. nigra and N. alba (both=C. spinipes).
LEIpy, JOS.
83. On the reproduction and parasites of Anodonta fluviatilis.
Proc. Acad. Nat. Sci. Phila.. 1883, 44-46.
A. ypsilophorus and A. Bonzi (?).

MULLER, OTTo FRIEDR.
1776. Zoologiae Danicae prodromus, ete. Hafniae, 1776. (274 pag.)

NORTH AMERICAN SPECIES OF THE GENUS ATAX 257

1781. Hydrachnz, quas in aquis Daniae palustribus, etc., Lipsiae,
1781. (88 pp., 11 pls.)
Describes 4sp., Hydrachna crassipes (Atax), H. grossipes (ident. ’)
H. spinipes (Cochleophorus), H. vernalis (Cochleophorus). Es-
_) tablished Hydrachna to include all Water-mites.
NEUMAN, C. J.
80. Om Sveriges Hydrachnider, aus Konig]. Svenska Vet.-Akad.
Hndlegr., xvii, (123 pp. 14 pls.). Separate, 1880.
OSBORN (H.) AND UNDERWOOD (L.).
86. Preliminary List of the Species of Acarina of North America.
Can. Ent., xviii, 1886, 4-12.
Refer to ‘‘A. hwmerosa’’ and ‘‘A. ypsilophorus,’’ with the query
after each, ‘‘ where described ?’”’
PFEIFFER, CARL.
24. Naturgeschichte deutscher Land-und Siisswasser-Mollusken. (3
parts). Cassel, 1821; Weimar, 1824, ’28.
Vol ii, p. 27-28, describes Ataw ypsilophorus as Limnochares an-
odontae.
PIERSIG, RICH.
93a. Beitrige zur Hydrachnidenkunde, Zool. Anz., xvi, 1893,
393-399.
Desc. A. triangularis, n. sp. (Cochleophorus deltoides).
94b. Sachsens Wassermilben, Zool. Anz., xvii, 1894, 2138-216.
Lists A. crassipes, A. figuralis, A. intermedius, A. Bonzi, A.
ypsilophorus; proposes genus Cochleophorus and lists C. spini-
pes, C. deltoides, C. vernalis.
96. Beitrage zur Kentniss der in Sachsen einheimischen Hydrach-
den-Formen. Leipsig, 1896. (71 pp.).
Chars. genera.—A. ypsilophorus (Bonz), A. intermedius Koen.,
A. Bonzi (Clap.), A. figuralis Koch, A. crassipes (Miill.), A. acu-
leatus Koen., A. tricuspis Koen., C. spinipes (Miill.), C. delioides
Piersig, C. vernalis Koch., C. verrucosus (Koen.), C. callosus
(Koen.)
97. | Deutchlands Hydrachniden. Bibliotheca Zoologica, xxii. (5
parts issued.)
Includes the species listed in previons reference.
97a. Bemerkungen zur Hydrachnidenkunde. Zool. Anz., xx, 59-61.
Proposes new genus HEncentridophorus for A. spinifer Koen.
from E. Africa, and Najadicola for A. ingens Koen. from
Canada.
RATHEE, JENS.
1797. Skrivter af Naturhist. selsk., iv, pt. 1,175. Pl. x. 1797.
Redescribes A. ypsilophorus as Trombidium notatum.
Say, THOMAS.
21. An account of the Arachnides of the United States. Jour.
Acad, Nat. Sci., Phila., ii, 1821, 59-83. LeConte’s Ed. of Writings,
1859, ii, 9-21.
Describes Hydrachna triangularis (prob. = A. ypsilophorus].
17

1 OSD aaa kant
a a

958 ROBERT H. WOLCOTT:

STOLL, OTTO.

87. Hydrachnidae. Godman and Salvin’s Biologia Centrali-Ameri-
cana; Zool. Part lix, 1887, 9-15. Pls. vii-ix.

Desc. A. alticola, A. dentipalpis and A. septem-maculatus.
VAN VLEET, A. H.

96. Ueber die Athmungsweise der Hydrachniden. Zool. Anz., xix,
1896, 505-507.

W ALCKENAER [CHAS. A. DE] AND GERVAIS [PAUL].

44, Histoire Naturelle des Insectes. Aptéres. Tom. iii; Paris; 1884.
Neglecting all the advances made since the time of Dugés (84),
enumerates under Atax 16 species belonging to several genera,
among them A. crassipes Miill., A. grossipes Miill., A. spinipes
Mill. (Cochleophorus), A. vernalis Miill. (Cochleophorus), A. fur-
cula Koch and A. freniger Koch (= C. spinipes (Mill.)

Woxcort, R. H. ;

98. |New American Species of the Genus Atax (Fab.) Bruz. Zool.
Bull., i, 1898, 279-285.

EXPLANATION OF PLATES.

PLATE XXVIII.
Fig. 1. A. crassipes. Outer side, right palpus. Male. x 180.
Fig. 2. A. crassipes. Three basal segments of leg I. x 180.
Fig. 3. A. crassipes. Genital area of female. x 250.
Fig, 4. <A. aculeatus. Outer side, right palpus. Female. x 180.
Fig. 5. <A. aculeatus. Posterior end of the body of a female, from

the unmounted specimen. No attempt has been made to mark the loca-
tion of hairs, but proportions and relative positions of parts shown are
correct. x 180.
Fig. 6. A.aculeatus. Spine at the side of the genital opening of
female. x 595.

Fig. 7. A. pectinatus. Outer side, left palpus of female. x 175.

Fig. 8. A. pectinatus. Distal segment, leg I. Male. x 340.

Fig. 9. A. pectinatus. Mandible. x 175.

Fig. 10. A. pectinatus. Half of genital area of female. x 175.
PLATE XXIX.

Fig. 11. A. intermedius. Outer side, left palpus of female. x 250.

Fig. 12. A. intermedius. Distal joint, hind leg of female. x 180.

Fig. 13. . abnormipes. Outer side, left palpus of female. x 260.

A

A

A
Fig. 14. A. abnormipes. Anteriorsurface,right leg IV of male. x175.
Fig. 15. A. abnormipes. Claw of right leg ILof male. x 540.
Fig. 16. A. indistinctus. Outer side, right palpus of female. x 250.
Big. )17, \ iA.
4,5and6. x 180.

A

Fig. 18. A. serratus. Mandible of female. x 185.

. indistinctus. Ventral surface, leg IV of male—segments ~

PLATE XXIX

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NORTH AMERICAN SPECIES OF THE GENUS ATAX 259

PLATE XXX.
Fig. 19. A. serratus. Outer side, right palpus of female. x 170.
Fig. 20. A. serratus. Inner side, part of left palpus. x 170.
Fig. 21. A. serratus. Distal segment, right leg 1V offemale. x 185s
Fig. 22. A. serratus. Claw ofright leg II. x 540.
Fig. 23. A. serratus. One half of genital area of female. x 170.

Fig. 24. A. fossulatus. Outer side left palpus of male. x 180.

Fig. 25. A. fossulatus. Distal segment of first pair of legs. Female.
x 250.

Fig. 26. A. fossulatus. Genital area of male. x 180.

Fig. 27. A. stricta. Distal segment of first pair of legs. Male. x 250.

Fig. 28. A. stricta. Genital area of male. x 250.

PLATE XXxXI.

Fig. 29. A.arcuata. Outer side, right palpus of female. x 250.

Fig. 30. A. arcuata. Distal segment, last pair of legs, anterior
surface. Female. x 190.

Fig. 31. <A. ypsilophorus. Outer side, right palpus of female. x 180.

Fig. 32. A. ypsilophorus. Posterior surface, distal segment, right
leg IV. Female. x 180.

Fg. 33. A. ypsilophorus. Posterior end of body of female from ven-
tral aspect. x 180.

- Fig. 34. A. tumidus. Outer side, left palpus of female. x 250.

Fig. 35. A. twmidus. Anterior surface of distal segment, leg IV.

Female. x 190.

PLATE XXxXil.

Fig. 36. A. twmidus. Mandible. x 180.

Fig. 37. A. tumidus. Outline of the epimera and maxillary shield
of female. x 55.

Fig. 38. A. tumidus. Genital area of female. x 180.

Fig. 39. A. (N.) ingens. Inner side, palpus of male. x 180.

Eig. 40. A.(N.)ingens. Segment 6, first leg, anterior surface.
Male. x 250.

Fig. 41. A.(N.) ingens. Mandible. x 180.

Fig. 42. A.(N.) ingens. Outline of epimera and genital plate of one
side. Female. x55. The line represents the median line of the body.

Fig. 43. A.(N.) ingens. Genital areaof male, penis exserted. x 76.

WANN

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