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BULLETIN OF THE UNITED STATES FISH COMMISSION. 
9. Diurella sulcata Jennings (pi. n, figs. 21^26, and pi. xiii, figs. 113, 118. 119). 
Synonyms: Rattulus sulcatus Jennings (1894); Coelopus brachiurus (?) or Raft ulus cryptopus Bilfinger (1894). 
Distinguishing characters. — This species is to be known by the short, curved body, with two 
prominent constrictions about it; by the very short, equal toes, attached to a foot which is usually 
withdrawn into the body, and by the unarmed anterior edge of the lorica. It bears some resem- 
blance to Diurella brachyura Gosse, but is distinguished from the latter by the equal toes, the 
constrictions, and the general form. It also resembles Diurella cavia Gosse, but is much larger, 
and the posterior part of the lorica ends in an entirely different manner in the two species. 
External features. — The body is nearly cylindrical and strongly curved, the dorsal line forming 
nearly an arc of a circle. The foot is usually retracted within the lorica (fig. 25) , so that the ven- 
tral line meets the dorsal in a sharp angle, giving a very characteristic feature of this animal; 
when the foot is extended, however, as in fig. 24, this angle does not appear. Surrounding the 
body a little in front of the middle are two pronounced grooves, which separate off the anterior 
part of the lorica from the remainder. There are no pronounced teeth nor spines at the anterior 
margin of the lorica, though the dorsal edge projects a little farther than the ventral, so that this 
might perhaps be described as a very slightly marked tooth. On the dorsal surface of the lorica 
(apparently in the middle line, though this is very difficult to determine in an animal of this form, 
in which a dorsal view is rarely obtained) there is a shallow furrow, between two slight ridges, 
extending back about to the first transverse groove. This furrow is striated transversely. In 
some specimens this furrow seems scarcely to exist at all. The ridge to the right of the furrow is 
a little higher than the one to the left. 
Corona. — The corona has the usual two sets of cilia — those about the outer edge and a small 
curve on each side of the mouth. In addition to these, the following structures may be distin- 
guished: (a) A large fleshy dorsal process, pointed in side view (fig. 24). but nearly rectangular 
from above; (6) two small antenna-like processes, one on either side of and below the dorsal 
process; (c) a large, rounded, central projection of the coronal surface below the dorsal process 
(fig. 24). 
Antennae. — The dorsal antenna is in the median furrow, about halfway back to the first 
circular groove. The lateral antennfe, very minute, are in the usual position, on the posterior 
third of the lorica. 
Foot. — The foot is scarcely distinguishable as a separate structure, since it is small and is 
habitually retracted within the lorica (fig. 25). It can be extended, however (fig. 24), and is a 
very short joint of the usual form. 
Toes. — The two toes are equal in length, very short, and are usually concealed for half their 
length within the lorica, the tips projecting downward (fig. 25). When the foot is extended, the 
toes point forward (fig. 24.) Each toe is accompanied on its outer side by a substyle aborit one- 
third its own length. 
Internal organs. — The mastax is very large, and contains large, well-developed troplii. These 
are unsymmetrical, the right manubrium being a mere slender bristle, much smaller than the left 
(fig. 26). The mucus reservoir is large, and divided by a longitudinal partition into two equal 
halves. The contractile vacuole is very small, lying above the mucus reservoir, on the right side 
of the intestine. The remainder of the internal organs call for no special mention. 
Measurements. — Length of body without toes. 0.17 to 0.18 mm. ; length of toes, 0.03 to 0.035 mm. 
History. — This species was described by the present author in 1894 as Rattulus sulcatus. In 
the same year Bilfinger ( 1894) described and figured it, considering it to be possibly Gosse's Coelopus 
( Diurella ) brach gurus. Since that time it has been mentioned, with notes, by Stenroos (1898) and 
figured by Jennings (1901). 
Distribution. — Diurella sulcata Jennings is very common in summer in the vegetation of our 
lakes. I have found it in the following localities: Lake St. Clair: Old Channel, Charlevoix, Midi.; 
West Twin Lake, 6 miles from Charlevoix, Mich.: Put-in Bay Harbor and East Harbor, Lake 
Erie. Kellicott, (1896) found this species in Sandusky Bay. Lake Erie. 
In Europe: Wurttemberg, Germany (Bilfinger, 1894); Lake Nurmijarvi in Finland (Stenroos, 
1898). 
