246 GEOL. AND NAT. HIST. SURVEY OF MINNESOTA. 



rather sparsely hairy; the beak is blunt, but, on account of the spread- 

 ing of the extremely wide fornices, does not appear so except under 

 pressure. 



The beak reaches nearly to the lower shell margin. The antennules 

 are narrow, one or more of the setoe being elongated. The dorsal 

 margin is either nearly straight or strongly arched behind; in either 

 case the greatest height of the shell is back of the middle. The pig- 

 ment fleck is large. The post-abdomen is just as in A. cosfata, but the 

 lateral row seems to be of spines rather than fringed scales. The shell 

 is marked by rather evident or indistinct lines. The form agrees 

 pretty well with Schoedler's figure, except that the posterior shell 

 margin is much higher. The antennce have eight setse, but the last 

 one is very weak. The terminal setce seem sometimes to be spined, as 

 figured by Schoedler, but in some specimens they are perfectly 

 smooth. There is a circlet of spines on the second joint of the setose 

 ramus. There is a hair on the inner aspect of the protuberance of the 

 labrum. The eye is somewhat nearer the pigment fleck than is the 

 end of the beak. 



There seems to be no occasion for separating the American form 

 (Plate LX, Fig. 3), in which the length varies between 0.41 mm. and 

 0.55 mm. The smaller forms have the back most rounded, while a 

 specimen 0.55 mm. long will appear very like A. quadrangidaris. Males 

 are elongate; hook of first foot strong, accompanied by a heavy growth 

 of small spines; terminal claw of abdomen with a minute spine. 



*Alona porrecta Birge. 



Sub rectangular; ventral line nearly straight; valves marked by 

 longitudinal striae; beak short. Post-abdomen truncate, with about 

 twelve teeth, three or four of which at the end are larger, and a row of 

 hairs above the teeth. Male similar. Length 0.34 mm. Distinguish- 

 able from the following small species in the armature of the post- 

 abdomen. 



The lower angle of the post-abdomen is acute. The claws are not 

 serrate, but possess the basal spine. The post-abdomen is said to re- 

 semble that of A. tenuicaudis in its armature, but not otherwise. 

 This species is not enumerated by Professor Birge in his List of Crus- 

 tacea Cladocera from Madison, Wisconsin [1891], and we are left in 

 doubt whether the species is abandoned or not. 



Alona stagnalis Daday. 



" Rostro longisculo, paulam curvato, acuminato; macula cerebral! oculo minore) 

 jabro processu medial! glabro; testa corporis longitudinaliter, manifeste striata, 

 liuea dorsali rotundata, margine ventrali medio parnm arcuato, setaa ubiqne me- 



