ROTATORIA OF THE UNITED STATES. 
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5. Diurella insignis Herrick (1885) (pi. n, figs. 15-18). 
Distinctive characters . — This species may be known by the long, slender, curved body; the two 
slightly unequal teeth at the anterior margin of the lorica, and the two unequal toes, the longer 
one (in adults) a little less than one-half the length of the lorica. It shows much resemblance to 
Diurella tenuior Gosse, but is distinguished from it by the possession of two teeth at the anterior 
margin and by the more elongated form. The toes are almost identical in the two species. 
External features . — The body is more elongated and slender than in any other species with 
which I am acquainted, and is gently curved. It tapers slightly from a point not far from the 
anterior end to the foot. The anterior portion of the lorica, the head-sheath, is set off from the 
remainder by a constriction, and is provided with a number of longitudinal plaits at which folding 
takes place when the head is retracted. At its anterior edge, a little to the right of the dorsal line, 
it bears two teeth. These are of unequal size, the right one being considerably the longer. The 
length of this right tooth varies considerably in different specimens; it seems to be especially prom- 
inent in young specimens (pi. n, fig. 18). The two teeth are separated by a considerable interval. 
The left tooth is small and is very easily overlooked, especially when the corona is extended, so that 
specimens of this species are likely to be thought to have only a single tooth if a careful examina- 
tion is not made. 
From the teeth a low ridge extends backward, having its edge to the right, even with the 
right tooth, and sloping gradually to the left. The ridge is very inconspicuous and easily over- 
looked. It extends backward for three-fourths of the length of the lorica and is marked as usual 
by transverse striations. 
Corona . — The corona is of the usual character, having two marginal curves of cilia and two 
about the mouth. There is a short, thick, dorsal process, and two lateral projections bearing cilia 
(as in Diurella stylatci Eyferth, pi. hi, fig. 31) ; other processes I have not seen. 
Antennae . — The dorsal and left lateral antennas I have not been able to find in this species; 
the right lateral antenna is in the usual position on the posterior fourth of the body (pi. u,fig. 16). 
Foot . — The foot is of the usual short conical form, obliquely attached to the lorica, so that it 
may turn to the right, but not to the left. 
Toes . — The toes (fig. 17) are almost identical with those of Diurella tenuior G-osse, save that 
they are longer. The left toe in an adult animal (pi. n, figs. 15 and 16) is a little less than one- 
half the length of the body, while in a young specimen (fig. 18) it is considerably more than 
one-half the length of the body. The right toe is one-half the length of the main toe, or a little 
less. Just outside the base of the main (left) toe there is a substyle, which is one-half the length 
of the right toe. At the base of the right toe there is a minute, rudimentary substyle. 
Internal organs . — The trophi (see fig. 18) are very unsymmetrical, as in Diurella tigris Muller 
and D. tenuior Gosse. The right malleus is very small and slender, though perhaps not quite so 
much reduced as in the two species last mentioned. The single eye is attached to the brain near 
its posterior end; in a dorsal view it lies considerably to the left of the ridge or striated area on 
the lorica (fig. 16). The other internal organs call for no special remark. 
Measurements . — Total length, 0.32 to 0.37 mm.; main toe, 0.10 to 0.12 mm.; shorter toe, about 
0.05 mm. 
History . — This species was described by Herrick in 1885. Herrick's description was brief and 
his figure extraordinarily poor, and as the species has not hitherto been found again, it has usually 
been relegated to the limbo of “doubtful species.” But Herrick’s description fits very well the 
specimens which I have, while his figure looks as if it had been drawn from memory. The 
animal has not again been mentioned since Herrick’s paper. 
Distribution . — Herrick found Diurella insignis in Minnesota. I have found it to be rather 
rare, but somewhat widely distributed amid the vegetation of lakes, ponds, and streams. My 
records show it to have been observed in the following localities: Put-in Bay Harbor and East 
Harbor, Lake Erie; inlet on Starve Island, close to South Bass Island, in Lake Erie; swamp on 
Presque Isle near Erie, Pa.; East Sister Lake near Ann Arbor, Mich. 
This species has not been found in Europe. 
