ROTATORIA OF THE UNITED STATES. 
339 
main toe is a substyle (perhaps the rudimentary right toe), which tapers very rapidly. Owing to 
its slenderness and close approximation to the main toe it is very difficult to determine the length 
of the substyle. In one case it appeared to be from one-third to one-half the length of the main 
toe. It is very easily overlooked. 
Internal organs. — The troplii are a little unsymmetrical. The mucus reservoir is divided 
into two equal halves, in spite of the fact that one of the toes has become rudimentary. 
Measurements. — Length of body, 0.18 mm.; of toe, 0.05 mm.; total, 0.23mm. 
History. — This species was described by Gosse (without a figure) in 1851. It is figured and 
described by G-osse (1889) in Hudson & Gosse’s Monograph. No description or figure of this 
species has been given since, though Bilfinger (1894) and Eckstein (1895) have a few notes on it. 
Eyfert.h (1885) thought it might be identical with Diurella stylata Eyferth, though the two seem 
not to have the remotest resemblance. 
Distribution. — This species has not been found in the United States, and my figures and 
description are from specimens kindly sent me by Mr. C. F. Rousselet, of London, England. 
In Europe: England (Gosse, 1851, 1889); Ireland (Hood, 1895); Wurttemberg, Germany 
(Bilfinger, 1894); Muggel-See, Germany (Eckstein. 1895); bayous of the Rhine (Lauterborn, 1898). 
34. Rattulus pusillus Lauterborn (pi. ix, figs. 81-85). 
Synonym: Mastigocerca pusilla Lauterborn (1898). 
Distinguishing characters. — This species may be known by its minute size, the short, plump 
body without teeth or spines, and the rod-like toe about four-fifths the length of the body. 
External features. — The body is short and thick, without striking external features of any 
sort. The head-sheath is marked off by as light constriction from the remainder of the body. 
Considerably to the right of the dorsal median line is a small, shallow furrow running obliquely 
backward and corresponding to the striated area of other Rattuliclce. This is very inconspicuous, 
so that it may very easily be overlooked. In some specimens it appears to extend less than half the 
length of the animal; in others it passes to a point considerably back of the middle, while in 
still others it is scarcely observable at all. Possibly the furrow disappears when the lorica is 
distended, as by strong contraction. The form of the lorica shows considerable variation, as will 
be seen by a comparison of the figures given on plate ix. There are no teeth, spines, or notches at 
the anterior edge of the lorica. 
Corona. — This is of the usual structure. There are two curves of cilia at the sides of the 
coronal disk and two about the mouth. A median dorsal club-shaped process exists, but no lateral 
processes are to be observed. 
Antennce. — The left lateral antenna is in the usual position (fig. 83), but the others have not 
been observed. 
Foot. — The foot is very small: it shows no peculiarities in other respects. 
Toes. — There is a single bristle-like toe, usually about four-fifths as long as the lorica, but vary- 
ing. In some cases it is little more than half the length of the lorica. It is nearly straight, though 
there is a slight bend a short distance from its base, like that to be observed in Rattulus stylatus 
Gosse. Closely appressed to the base of the main toe, so as to be very inconspicuous, is a short 
substyle, about one-sixtli the length of the main toe. 
Internal organs .' — These offer nothing peculiar. The trophi are of the usual type, the left side 
being considerably more developed than the right. 
Measurements. — Length of body, 0.085 to 0.11 mm.; of toe, 0.06 min.; total, 0.14 to 0.17 mm. 
History. — Lauterborn (1898) lists this species under the name Mastigocerca pusilla , but does 
not give a description. Through the kindness of Dr. Lauterborn I received a sketch of his animal, 
which shows that it is identical with the rotifer which I have found in the Great Lakes. I have 
therefore used Lauterborn's specific name. 
Distribution .— Rattulus pusillus is rare. I have found it in East Harbor. Lake Erie, near 
Sandusky, Ohio, and in ponds on Middle and South Bass islands, in Lake Erie. Mr. Rousselet has 
sent me specimens collected at Hanwell, in England. Lauterborn (1898) found it in the bayous 
of the Rhine. 
