ROTATORIA OF THE UNITED STATES. 
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10. Diurella cavia G-osse (pi. hi, figs, 35 and 36). 
Synonym: Ccelopus cavia G-osse (1889) . 
Distinctive characters. — This species is to be recognized by the very small, plump body, with- 
out teeth at the anterior margin of the lorica, and the projection of the lorica as a large, rounded 
protuberance over and behind the foot, so that the foot arises from the ventral surface of the body, 
and by the short, equal toes. It differs from D. porcellus Gosse and D. intermedia Stenroos in the 
absence of teeth at the anterior margin of the lorica and in the equal toes, together with differences 
in general form. From D. brachyura Gosse it differs in the short, thick body and the large, 
rounded backward projection over the foot and in the equal toes. From I). sulcata. Jennings, its 
nearest relative, it differs in its much smaller size and in the great posterior enlargement projecting 
as a large, rounded protuberance over the foot, giving the animal an entirely different appearance 
from the last-named species. 
External features. — The lorica is short and thick, arched dorsally and only slightly curved 
ventrally (fig. 36). The lorica projects backward as a large, hollow protuberance, extending 
considerably back of foot. There are one or two slight constrictions about the middle of the body, 
much as in D. sulcata Jennings, but less marked. The anterior margin of the lorica is without 
teeth. Extending back from the anterior margin to nearly the middle of the lorica, a little to the 
right of the middle line, is a depressed, striated area, its two edges being a little elevated. 
Corona. — The corona bears the usual thick dorsal process; in other respects it has not been 
specially studied. The antennae I have not seen. 
Foot. — The foot is very small, scarcely noticeable as a separate joint. It is situated consider- 
ably in front of the posterior end. on the ventral surface. 
Toes. — The two toes are equal in length, the length being somewhat less than the diameter of 
the lorica. In the specimen studied by the author the two toes extended backward and were 
crossed (fig. 35), This is doubtless by no means the rule. In Mr. Gosse’s specimens the toes were 
turned forward, as in D. porcellus Gosse. There is a substyle at the base of each of the toes (not 
shown in the figures) . The internal organs seem to offer nothing exceptional. In the single speci- 
men at my disposal I was not able to make out the trophi. 
Measurements . — Length of body without toes, 0.115 mm.; length of toes, 0.032 mm. 
History. — This species was described as Ccelopus cavia by Gosse in Hudson & Gosse’s Mon- 
ograph of the Rotifera (1889). It has not since been described or figured. 
Distribution . — I have found but a single specimen of this species, from the northern swamp 
on Middle Bass Island, in Lake Erie. 
In Europe: Epping Forest, England (Gosse, 1889); Ireland (Glasscott, 1893) ; Austrian Poland 
(Wierzejski, 1893). 
11. Diurella brachyura Gosse (pi. m, figs. 32-34, and pi. xm, figs. 114 and 115). 
Synonyms: Monocerca brachyura Gosse (1851); Diurella rattulus Eyferth (1878 and 1885); also Eckstein (1883): 
Acanthodactylus rattulus Tessin (1886); Ccelopus brachyurus Hudson & Gosse (1889); Rattulus palpitatus 
Stokes (1896). 
Distinctive characters . — This species is to be known by the small, curved body, less plump 
than in D. porcellus Gosse and D. cavia Gosse; the lack of teeth at anterior margin of lorica; the 
fact that the foot is not on the ventral surface; and the nearly equal toes, of length about equal to 
diameter of lorica. It is nearest to D.' cavia, from which it is distinguished by the more slender 
body, tapering to the posterior end, and the fact that the foot is not on the ventral surface. 
External features . — The body is cylindrical in form, much more slender than in D. porcellus 
Gosse, and tapers toward the posterior end. In extended specimens the thickest part of the body 
is the middle, the head region being a little narrower (fig. 32). The body is curved, so that the 
dorsal line forms nearly an arc of a circle. Together with the toes, which continue the curve of 
the body (when not bent up against the lorica) , a full semicircle is thus formed. The head-sheath 
is not sharply set off from the remainder of the lorica, though a slight constriction between the 
two is evident. There are no teeth at the anterior margin of the lorica. The head-sheath may be 
folded longitudinally when the head is retracted, as in many other species. At such times one 
of the folds on the left extends a little beyond the others, forming thus a slight rounded, very 
inconspicuous, projection (fig. 33). This projection disappears when the head is fully extended. 
Usually no ridge is apparent, though on some specimens there is evidently a slight elevation of the 
