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BULLETIN OF THE UNITED STATES FISH COMMISSION. 
lorica in the usual position of the ridge, to the right of the dorsal line. Careful examination of 
favorable specimens shows that a striated area, such as marks the ridge when it exists, is always 
present (fig. 33). This is broadband extends back to about the middle of the body; it has two sets 
of the striations, meeting each other along a central rliaphe. 
Corona. — The corona is of the usual character. It bears a single thick dorsal process (fig. 32) , 
and apparently two very slender lateral processes, though of these I could not be quite certain. 
Antennal. — The dorsal antenna is in the striated area, a little behind the constriction setting 
off the head-sheath. The lateral antennae are in the usual position, on posterior third of body. 
Foot. — The foot forms a continuation of the tapering body at its posterior end, not being 
pushed forward on the ventral side, as in D. cavia Gosse and D. porcellus Gosse. It is of the usual 
short conical form. 
Toes (figs. 34 and 114). — The two toes are very nearly equal, the left being a very little 
longer than the right. Frequently the tip of the right toe lies against the left, but this is by no 
means always true. The longest toe is about equal in length to the diameter of the body. At the 
base of each toe on its outer side is a single substyle, about one-third the length of the toe. 
Internal organs. — The trophi are of the usual character, the right manubrium being much 
reduced. The small contractile vacuole (fig. 32, eu.) lies above the mucus reservoir and contracts 
very rapidly (according to Stokes (1896) 40 times per minute) . The rest of the internal organs call 
for no special remark. 
Measurements. — Length without toes, 0.10 to 0.13 mm.; length of toes, about 0.03 mm. 
History. — This species was described by Gosse in 1851 as Monocerca bracliyura. Eyferth 
(1878) proposed, for a form which he said was much smaller than D. stylata, the name Diurella 
rattulus , but he gave no further account of the animal. Eckstein (1883) described and figured 
the animal under the name proposed by Eyferth. Tessin (1886) gave a few notes on the animal 
under the name Acanthodactylus rattulus. In Hudson & Gosse’s Monograph (1889) this species was 
transferred to Mr. Gosse’s new genus Coelopus, receiving the name Coelopus bracliyurus. As this 
genus was based on an error, the species must of course go back to Diurella. Finally, Stokes 
(1896) described this as a new species, under the name Rattulus palpitatus, the specific name 
relating to the rapidity of the pulsations of the contractile vacuole. Stokes’s description and figure 
apply in every detail to I), bracliyura, so that there was no reason for giving. the animal a new name. 
Figures of this species have also been given by Jennings (1900 and 1901). 
Distribution . — This species is not very common and seems as a rule to inhabit swampy ponds. 
I have recorded it from East Harbor, Lake Erie, near Sandusky, Ohio; from the Huron River at 
Ann Arbor, Mich.; from pools near Hanover, 1ST. H.; and from marshy ponds on North, Middle, 
and South Bass islands, and on Presque Isle, all islands in Lake Erie. Kellicott (1888) reported 
its presence in the Shiawassee River at Corunna, Mich.: Stokes (1896, as Rattulus palpitatus) 
found it near Trenton, N. J. 
In Europe: England (Gosse, 1889) ; Ireland (Glasscott, 1893) ; near Rostock, Germany (Tessin, 
1886); Wurttemberg, Germany (Bilfinger, 1892, as D. rattulus)-, Finland (Levander, 1894, as D. 
rattulus) . 
12. Diurella dixon-nuttalli n. sp. (pi. iv, figs. 40 to 44). 
Distinctive characters. — This species is to be known by the absence of teeth at the anterior 
margin of the lorica and by the two toes, one about two-thirds the length of the other. It is closely 
related to D. bracliyura Gosse, from which it differs in the greater inequality of the two toes, as 
well as in general form. (Compare the figures of the two species.) From D. sulcata Jennings 
and D. cavia Gosse this species differs in having unequal toes. 
External features. — The body is nearly cylindrical, somewhat curved, and tapers toward the 
posterior end. The dorsal line is convex, the ventral line nearly straight, or concave. The head- 
sheath is set off from the remainder of the lorica by a constriction, and lias. a number of longitudinal 
folds, where it yields when the head is retracte.d. It is without teeth at its anterior edge. On the 
dorsal surface of the lorica a short furrow extends backward from the anterior margin to a point 
some distance behind the constriction which separates the head-sheath from the remainder of the 
body (fig. 40). This evidently corresponds to the striated area of other species. 
Corona. — The corona bears the usual median dorsal club-shaped process, as well as a number 
of other prominences (fig. 40). Otherwise it seems to be of the usual character. 
