ROTATORIA OF THE UNITED STATES. 
815 
and shorter, while the character of the toes is not clearly shown (nor described in the text). It is 
possible, therefore, that Wierzejski’s species is not the same as Dmrella stylata Eyferth. 
Hood (1895) gives good figures and a description of this animal under the name Rattulus 
bicornis. Minkiewicz (1900) again describes this species as new, under the name Mastigocerca 
birostris. 
Distribution. — This species is not common, though it sometimes occurs in large numbers in 
swampy ponds. I have recorded its presence in the following places: East Harbor, Lake Erie (near 
Sandusky, Ohio); pond near United States fish-hatchery, Put-in Bay, Ohio; Portage River, Ohio. 
In Europe: England (Western, 1893) ; Ireland (Hood, 1895) ; Wiirttemberg, Germany (Bilfinger, 
1892); bayous of the Rhine (Lauterborn, 1898); Austrian Poland (Wierzejski, .1893, as Cadopus 
similis ); near Kharkow, Russia (Scorikow, 1896); Lake Bologoe, Russia (Minkiewicz, 1900). 
8. Dmrella rousseleti Yoigt (pi. iv, figs. 37-39). 
Synonym: GSSlopus rousseleti Voigt (1901). 
Distinctive characters. — This small species is at once known by the nine projecting points at 
the anterior margin of the lorica, the upper right-hand one being a little larger than the others. 
The animal does not closely resemble other species of Diurella; its closest relatives seem to be 
Rattulus stylatus Gosse and Rattulus pusillus Lauterborn. But the shorter toe is about half the 
length of the longer one, so that it is necessary to place the animal with the Diurellas. 
External features. — The small body is usually rather short and thick (fig. 37), slightly bent, 
and tapering backward in conical fashion to the toes. The proportions of the body vary consid- 
erably, as will be seen by comparing fig. 37 and fig. 39. The large head-sheatli is marked off: from 
the remainder of the lorica by a .slight constriction. The entire circumference of the head is set 
with large projecting points or teeth, there being nine of these in all. They are somewhat larger 
on the right side than on the left, and the dorso-dextral one is a little larger than any of the 
others. These teeth are formed as projections of the plaits of the head-sheath, and are represented 
in much less pronounced form, as mere rounded projections, in some other species. The larger 
dorso-dextral tooth evidently corresponds to the single tooth of Diurella tigris Muller and other 
single-toothed species. Between the teeth the lorica in D. rousseleti forms furrows which are 
flexible. These fold when the head is strongly retracted, so that the teeth are brought into close 
contact. Between the two dorsal teeth is a somewhat larger furrow, which jmsses backward to 
the constriction which separates the head-sheath from the body. This furrow perhaps represents 
the “ striated area ” of other species. 
Corona. — This bears, according to Yoigt (1901), a very long central dorsal process, bent 
upward and showing wavy lines on its lower side. 
Antennce.— The dorsal antenna is in the usual position on the dorsal side, near the constriction 
which separates off the head-sheath. The lateral antennae have not been observed. 
Foot. — The foot is a short, conical structure, of the usual form. 
Toes. — There are two toes (fig. 38), the right one being about one-half the length of the left. 
The two toes are very close together, and the right one is very slender, so that it is easily over- 
looked; the impression is then received that the animal has but a single toe. The longer toe is 
about one-third the length of the body, or a little less than one-third. It is very slightly curved, 
the concave side of the curve being dorsal. 
Internal organs. — According to Voigt (1901) there is a large red eye on the posterior end of 
the large brain. Trophi large, unsymmetrical. 
Measurements. — Length of body, 0.095 mm.; of toe, 0.03 mm. Length of the long anterior 
dorsal process of the corona, when extended, 0.0195 mm. 
History. — This species was described by Voigt, without a figure,, in 1901. Through the kind- 
ness of Herr Voigt I have received a quantity of material containing specimens of the animal, and 
have thus been able to study it at first hand. The figures herewith given are the first published. 
Fig. 39 is due to Mr. Dixon-Nuttall; the others I have myself made. 
Distribution. — Not yet been found in America. It should be looked for in small ponds. 
In Europe: Plankton of the Schoh-See, Heiden-See, and Schluen-See, near Plon, Germany 
(Voigt, 1901). Also found in England. 
