3 Uy pedi jy he a See ee Cie a acolo) a alee a an 
Se A oe ener oe ; } 
ENTOMOSTRACA OF MINNESOTA. 257 
*Pleuroxus hamatus Birge. 
PLATE LX, Fia. 1. 
This species is smaller than those of the preceding group and forms 
a transition to the two next, to be described, in the greater elongation 
of the shell, which is, however, higher and more strongly arched. 
The head and beak are much as in P. denticulatus. The lower margin 
is concave posterior to the middle and slightly convex at the posterior 
angle, which is unarmed. The lower margin is hairy. The markings 
are as in P. denticulatus, but, in addition, there is a set of horizontal 
strie all over the shell. The post-abdomen is widest in the middle 
and almost exactly as in P. denticulatus. The first foot bears a claw 
such as ordinarily distinguishes the males. 
The only specimens which I have seen were from the Tennessee 
river, near Waterloo, and near Decatur, in Alabama. My notes con- 
tain no reference to the minute striations, which could perhaps be 
hardly seen with the instrument employed. The process of the labrum 
is long and rather acute, the beak moderate, and the pigment fleck 
very large. The markings on the anterior of the valves are irregular 
and are inter-connected by cross lines or anastomoses. Ova two. 
(The genus Anchistropus has a hook upon the first foot, but is like 
Chydorus. ) 
*Pleuroxus gracilis Hudendorff. 
PLATE LXIV, Fias. 15, 15a. 
Pleuroxus unidens—Birge. 
An extreme among these elongated species, the length of body fall- 
ing little short of double the height. The dorsal line is very flat and 
slightly but evenly arched; the lower margin is evenly convex or 
nearly straight, covered by long pectinate bristles. The head is short, 
and the beak is long and sharp; the antennules are of moderate size, 
with a lateral seta one-fourth from the end; pigment fleck less than 
the eye; antennz rather long, with strong thorns on the termina] 
joints. The post-abdomen is long, as in P. hastatus, sides nearly par- 
allel; anal teeth sharp, small and numerous; claws pectinate, with two 
strong basal spines. The shell is strongly striate with longitudinal 
Striz, which are parallel with the different margins. Birge says that 
there is a reticulated area. The lower angle is rounded, and anterior 
to it is a small tooth directed backward. This species is distributed 
throughout the Mississippi valley. I have notes of it from Swan lake, 
near Decatur, Ala. It is often rather abundant about Minneapolis, 
but it is thought by Birge to be absent from the Eastern states. Almost 
all the specimens I have seen are very dark, often brown, so as to ap- 
pear to the eye like dark specks as they swim about. The length 
