so oo aig ib a ea 
T 
ENTOMOSTRACA OF MINNESOTA. 233 
the middle, and are serrated. The antennules are long and slender, 
but do not reach to the end of the rostrum. They have each a flagel- 
lum and sense hairs. The antenne are small and have eight (3¢¢ 
setze and two (4%°) spines. The labrum resembles that of A. leuco- 
cephalus, but is slightly prolonged at the apex. The intestine, cecum 
and color resemble those of Acroperus. There is a trace of a keel pres- 
ent on the back.’’ 
The specimens seen in Minnesota resemble this species very nearly, 
apparently, but there are some differences. The terminal claw of the 
post-abdomen has an increasing series of spines to the middle; there 
seems to be no lateral row of scales beside the anal teeth; the abdo- 
men is rather broad at the base and narrows toward the end. The 
shell is not square behind. The lower margin has a few long hairs 
anteriorly which are followed by a series of teeth, and in the concave 
part a somewhat longer set to a point just before the lower curved 
angle. 
The pigment fleck is nearly or quite as large as the eye. The an- 
tennule is shorter than the beak (which is almost as in Pleuroxus 
hastatus), and has a flagellum about midway; at its base it. is narrowed 
and inserted on a prominence. 
The embryo still in the brood-sae has a more elongate form and 
hexagonal reticulations upon the shell, while the antennules were 
longer than the very long beak, and the pigment fleck was smaller 
than the eye. Length of female 0.52 mm. The color is darker, and 
the striz more numerous, than in A. latissima. 
From a private letter we learn that this form is now regarded as 
simply a variety. 
SERIES B.—This section includes Leydigia, Graptoleberis, Dunhevidia (—Crepidocer- 
cus), Lynceus, Alona, Alonella, Pleuroxus, Phrixura, Chydorus, Anchistropus, Monospilus. 
GENUS LEYDIGIA Karz. 
In this genus, both the known species of which are found in 
America, the posterior part of the shell and body is emphasized at 
the expense of the anterior. The curved posterior margin is equal to 
the greatest height of the shell. The head and anterior part of the 
body are of the form characteristic of Alona; indeed, the whole body 
is in plan like Alona, but in the back part the organs are all enlarged. 
The general form of the body and abdomen recalls J/yocryptus; the 
post abdomen, in particular, is very like that genus. The last two 
pairs of feet are much enlarged. ‘The shell is usually irregularly 
marked with longitudinal strie; the lower margin is covered with 
long spine-like sete. The post-abdomenis armed with several sets of 
