338 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
Internal, organs.— The, internal organs are beautifully and clearly displayed in R. elongatus 
Gosse, rendering this perhaps the most favorable species that exists for a study of the anatomy. 
Beyond what was given in the general account of the anatomy of the Rattulidce (p. 288) , only two or 
three points need special mention. The brain is unsymme trical, there being a broad right lobe 
or division, and a narrow left lobe, shorter than the right one. This left lobe bears at its end the 
eye (fig. 108). The trophi are well developed and decidedly unsymmetrical, the left half being 
much larger and stronger than the right (fig. 107). 
Measurements. — Length of body, 0.38 to 0.40 mm.; of toe. 0.28 to 0.35 mm.: total, 0.06 to 
0.81 mm. 
History. — This species was described by Gosse (1889) in Hudson & Gosse’s Monograph of the 
Rotifera, as Mastigocerca elongata. A description (in Russian), without figure, is given by Scori- 
kow (1890). and figures are given by Jennings (1900 and 1901). Stenroos (1898) redescribed this 
animal (with a figure of the anterior end) as Mastigocerca grandis n. sp. His description of Masti- 
gocerca grandis fits Rattulus elongatus Gosse perfectly, the figure of the anterior end showing the 
form when the head is partly extended. 
Distribution. — In America: Rattulus elongatus Gosse is not rare in the quiet parts of rivers, 
ponds, and lakes, though large numbers are not usually found together. I have taken this species 
in the following localities: Put-in Bay Harbor and East Harbor. Lake Erie: pools at Hanover, 
N. H.; Portage River, Ohio: Huron River at Ann Arbor. Mich. It has also been found in San- 
dusky Bay, Lake Erie ( Kellicott. 1897 ) , and in waters connected with the Illinois River at Havana, 
111. (Hempel, 1898). 
In Europe: England and Scotland (Gosse, 1889) ; Ireland (Hood. 1895) : Wurttemberg, Germany 
(Bilfinger. 1892); bayous of the Rhine (Lauterborn, 1893); near Basel, Switzerland (Ternetz, 1892); 
Galicia, Austria-Hungary (Wierzejski, 1893); Lake Nurmi jarvi in Finland (Stenroos. 1898, as 
Mastigocerca grandis)-, Bohemia (Petr, 1890): near Kharkow, Russia (Scorikow. 1896). 
Also in Ceylon (Daday, 1898). 
33. Rattulus stylatus Gosse (pi. x, figs. 92-94). 
Synonyms: Monocerca stylata Gosse (1851); Mastigocerca stylata Gosse (1889). 
Distinguishing characters. — This species is to be distinguished by the very short toe, one-half 
or less the length of the body; by the irregular form of the body, with the head-sheath strongly 
set off from the remainder of the lorica, and by the unarmed anterior edge. There is no other 
species which bears a very close resemblance to it. 
External features. — In this species the body is more irregular in form than in perhaps any 
other. In dorsal or ventral view the body is ovate in general shape, truncate in front, but taper- 
ing rapidly behind to the toe. The posterior half of the body is thus conical, the apex of the cone 
being surmounted by the toe. In side view the ventral line is nearly even, while the dorsal line is 
arched (fig. 93). The head-sheatli or anterior portion of the body is smaller than the remainder, 
and setoff from it by a broad and deep furrow, so that in side view a prominent ‘’hump” is 
observed just behind the furrow (fig. 93). The furrow does not run uninterruptedly around the 
body, but is rather an irregular fold; it is farther forward on the ventral side than on the dorsal. 
The anterior margin of the lorica is without teeth or projections of any kind. 
Of this species I was able to study only mounted specimens (and these through the kindness 
of Mr. Charles F. Rousselet), and none of those available presented a directly dorsal view. It was 
therefore difficult to tell whether there was anything corresponding to the ridge or striated area or 
not. There seemed no sign of a ridge, but apparently there is a dorsal depression running backward 
from the median dorsal anterior margin of the lorica; this could not lie determined with certainty, 
however. The animal is clearly not so markedly unsymmetrical as are many of the Rattulidce. 
Corona. — The corona bears the usual club-shaped dorsal process; it has not been minutely 
studied in other respects. 
Antennae. — Dorsal and lateral antennae in the usual positions, as shown in figs. 92 and 94. 
Toes. — The main toe is very short, as compared with that of most of the species of Rattulus, 
being usually somewhat less than one-third the length of the body. It is slightly curved, the con- 
cavity of the curve being on the dorsal side, as shown in figure 93. Closely appressed against the 
