310 
Birge—Notes on Cladocera. 
sembling the sketches of the first specimen that the conclusion 
regarding the distinctness of the species seems warranted and it 
is described under the above name. 
Female.—The general form is rotund, resembling that of Ghy- 
dorus. The head is large, movable, much depressed. The forni- 
ces are broad and extend out into a broad, pointed flap of a ros¬ 
trum, which can be closely appressed to the valves. The dorsal 
outline is evenly arched to the posterior margin which is very 
short, practically absent. The posterior part of the ventral mar¬ 
gin rounds over into the dorsal with only a slight break and is 
fringed with somewhat straggling plumose hairs, longest in 
front. As seen from below the valves touch about the middle of 
the ventral edge' and are slightly separated at the posterior 
part. They also touch each other anteriorly. In the middle 
third of the length, the edge of each valve, instead of bending 
in toward the median line, is turned out, so that a rhomboidal 
space is here left between the valves. Just posterior to the 
center of the fold there is a sharp outfolding of the valve, form¬ 
ing a groove whose walls are produced ventrally so as to 
form a sort of curved hollow tooth. In the cavity of the larger 
fold lies the firs b foot and in the tooth lies the spine of this 
foot. 
The anterior margins of the valves are strongly convex, but 
not so tumid as is figured in A. emctrginatus by Norman and 
Brady (’67, P. XIX, Fig. 4). This structure of valves and first 
foot, which is characteristic of the genus, is less fully developed 
in A. minor than in A. emarginatus . In Norman and Brady’s 
figure the outfolding for the spine extends far back toward the 
posterior edge of the valve, and the spine is at least six times 
as large as in my specimens, where indeed it was difficult to 
discover it. The hook of the first foot is said by Sars to be 
“validus.” Norman and Brady call it a “long, cylindrical fal¬ 
cate process, denticulate on the edge, which is very conspic¬ 
uous. ” In none of my specimens was this true, but the hook is not 
very large, nor was it conspicuously exserted. 
The antennules are short conical, and bear the usual an¬ 
terior sense-hair and cluster of terminal sense-hairs which are 
about equal in length. The antennae have setae and have no 
