ENTOMOSTKACA OF MINNESOTA. 257 



*Pleurdxus haniatus Birge. 

 Plate LX, Fig. 1. 



This species is smaller than those of the precediug gronp 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 

 strise 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 striatious, 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 Ancliistroputi has a hook upon the first foot, but is like 

 Chydoms.) 



*Pleuroxus gracilis Hudendorff. 



Plate LXIV, Figs. 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; antennte rather long, with strong thorns on the terminal 

 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 

 striae, 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 



