ROTATORIA OF THE UNITED STATES 
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II. RATTULUS Lamarck. 
Generic characters . — One long toe, which is usually accompanied by another (the right toe), 
which is rudimentary, being not more than one-third length of main toe. The main toe usually 
more than half the length of body. Body cylindrical, oval, or ovoid; usually less curved than 
in Diurella. 
DESCRIPTIONS OF THE SPECIES STUDIED BY THE AUTHOR 
18. Rattulus gracilis Tessin (pi. v, figs. 45-49). 
Synonyms: Acanthodactylus gracilis Tessin (1886); Mast iijocerca iemis Gosse (1889). 
Distinguishing characters . — This species is to be distinguished by the elongated, only slightly 
curved body, with the head-sheath sharply set off, and with many longitudinal folds, the main 
(left) toe about one-half to two-thirds the length of the body and the rudimentary (right) toe about 
one-third the length of the main one. Its nearest relative is Diurella tenuior Gosse, from which 
it differs in having the shorter toe only one-third the length of the longer, in the less curved form, 
and the head-sheath sharply set off from the body. From Rattulus scipio Gosse it differs in hav- 
ing a shorter main toe, with the right toe longer in proportion, and in the marked folds of the 
head-slieatli when the head is retracted. 
External features . — The body is elongated and shaped much as in R. scipio , save that it is a 
little more curved, the dorsal line being markedly convex, while the ventral line is nearly straight. 
In a dorsal view the sides of the body frequently appear nearly straight, as shown in fig. 46. There 
is a ridge on the dorso-dextral side, extending from the foot to the head. On the head-sheath the 
ridge is less prominent; it ends anteriorly in a minute tooth (figs. 45, 47) . The ridge is transversely 
striated, the striations extending some distance to the left on the lorica. These striations are very 
inconspicuous, owing to the opaqueness of the internal organs, so that they can be seen only in 
especially favorable specimens. 
The head-sheath is sharply set off from the rest of the body by a deep constriction, and is as a 
rule much narrower than the rest of the lorica. It has many longitudinal folds, by which it can be 
folded into very small compass and the anterior opening almost completely closed when the head 
is strongly retracted (fig. 48). These folds almost disappear when the head is unusually extended 
(fig. 45). The dorsal portion of the head-sheath projects considerably beyond the ventral portion 
when the head is strongly retracted. 
On its right side, in the continuation of the ridge of the lorica, the head bears a single tooth 
(figs. 46-48). This is very minute, so that it is easily overlooked; it is not mentioned by Tessin 
(1896) nor Gosse (1889), though it was observed by Bilfinger (1894). 
As to the general form, it is perhaps possible to distinguish two varieties of .this species. 
Those which were sent me by Mr. Rousselet from Prescot, England, differed from the specimens 
found in America in the more slender body, perhaps a little more curved, and with the head- 
sheath not so sharply set off from the rest of the lorica. This English form is shown in figs. 45 
and 47, while American specimens are shown in figs. 46, 48, and 49. The differences do not seem 
to me sufficient to justify considering these different species. In other characteristics than those 
mentioned the specimens are alike. 
Corona . — The corona bears a prominent dorsal process; otherwise it has not been minutely 
studied. 
Antennce . — The dorsal antenna lies to the left of the ridge, at the junction of the head-sheath 
with the rest of the lorica (fig. 46, d. a). The two lateral antennae are in the usual position on the 
sides, on the posterior fourth of the body (fig. 46). 
Foot . — The foot is short and thick as compared with that of Rattulus scipio, and the lorica 
does not project over it in a free edge on the left dorsal side, as in the last-named species. 
Toes (fig. 46, 47). — The main or left toe is from one-half to two-thirds the length of the lorica. 
The smaller or right toe ( r . t.) is about one-third the length of the main one, and its distal end 
lies across the latter. At the left side of the main toe is a large substyle, about one-half or more 
of the length of the right toe. On the outer side of the right toe is a similar but very minute sub- 
style. The larger of the two mucus reservoirs is connected with the main or left toe; the smaller 
with the rudimentary right toe. 
F. C. B. 1902—21 
