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 setw 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. costata, 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 antenne have eight sete, but the last 
one is very weak. ‘The terminal sets 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. quadrangularis. 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 strizw; 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, paulum curvato, acuminato; macula cerebrali oculo minore3 
jabro processu mediali glabro; testa corporis longitudinaliter, manifeste striata, 
linea dorsali rotundata, margine ventrali medio parum arcuato, setas ubique me- 
