ENTOMOSTKACA OF MINNESOTA. 253 



species from the above seems to be the position and form of the head, 

 which is said to be blunt and nearly horizontal, as in Gamptocercus 

 rcctirostris. Is this a transition to Gmptoleberis? 



*Alonella pygiuaea Sars. 



Plate LX, Fig. 7. 



Pleuroxus transversus — Schoedler. 

 Alona transversa — P. E. Mueller. 

 Lynceus nanus — Fric. 

 AJoneUa pygmiea — Kurz. 



The form is rotund, much like species of Chydorus in the highly 

 arched dorsal outline; the beak is rather short and depressed; the 

 lower outline of the valves is very convex in front, and barely sinuate 

 behind, where it terminates in a minute spine. The shell is marked, 

 as in no other Lynceid, by lines running diagonally backward, and 

 only on the lower part reticulated, if at all. 



The post-abdomen is short, broad and rounded below; the claw has 

 a single basal spine. Length 0.20 to 0.28 mm. This is the smallest 

 member of the Cladocera. In form it so nearly resembles Chydorus 

 that upon first sight the writer took it for a member of that genus. 

 Our one specimen measured 0.25 mm. The shell is marked by plica- 

 tions rather than stripe, which arch over the back. 



Alonella striata Schoedler. 



This species is said to resemble A. exif/ua in habit and sculpture 

 of shell; the form is quadrangular and not greatly elevated in the 

 middle; the lower margin is nearly straight and fringed with bristles; 

 the posterior angle is rounded and unarmed. The antennules with 

 their setre extend beyond the beak; the pigment fleck is smaller than 

 the eye and half way to the beak. The post-abdomen is long and nar- 

 rowed toward the end; there are seven or eight anal spines, and two 

 spines on the terminal claw. Length about 0.5 mm. 



SUB-GENUS PLEUROXUS. 



Sectiou A, Pleuroxus (verus) Baird. 



This group of Lyuceids is most obviously defined by the long beak, 

 formed by the extension of the chitinous covering of the head. (There 

 is rarely a beak in the sense of that word as applied in the case of 

 SeaplwJeheris or Daphnia, but the antennules are simply attached to 

 low prominences on the under side of a broad shield-like projection 

 of the shell.) This beak-like projection is acute and often long and 

 either curved backward or even bent forward. The fornices, or lateral 



