Harring and Myers—The Rotifers of Wisconsin. 
567 
all projecting beyond the crenulate margin, which is much nar¬ 
rower than on the opposite side. The mannbria are very long and 
broad; a broad, thin lamella extends nearly to the posterior end 
on the dorsal margin. Below the posterior edge of the rami 
there is a curved rod imbedded in the walls of the mastax; the 
ventral end rests on the inner surface of the ramus, and the 
dorsal ends meet below the tips of the rami. 
The oesophagus is long and slender. Gastric glands, stomach- 
intestine, and ovary are normal. The bladder is formed by an 
expansion of the cloaca. The foot glands are very long, slender, 
and slightly club-shaped. 
The retrocerebral sac is extremely long, pyriform, clear, and 
vacuolate; the subcerebral glands are small, barely one fourth the 
length of the sac, and usually contain bacteroids, especially toward 
the posterior end. The ganglion is small and saccate, with the 
large eye-spot at its posterior end. 
Total length 600-800/x; toes 75/x; trophi 75 jjl. 
A variant of this species, described by Kirkman as Copens 
triangulatus and later by Daday as Notommata brachiata, develops 
three triangular humps, two lateral and one dorsal. As noted 
by Harring, a complete series of intermediates may be found 
between the humpless form and the fully humped form which is 
illustrated on Plate 3, figures 1 and 2. There is little doubt 
of their specific identity. The humpless form appears early in 
the spring, while the intermediate and fully humped do not oc¬ 
cur until June at Washington. The humpless form continues 
to occur throughout the summer, but in reduced numbers; the 
humped variant is far more abundant and continues until late in 
the fall. The humped form has not been reported from Europe; 
we have not had an opportunity to study typical European ma¬ 
terial, and it is possible that the American and African forms 
may be a distinct species. 
Notommata pachyura is common in weedy ponds in the United 
States, wherever collections have been made. 
