STATE GEOLOGIST. 99 



Sp. 11. Alona dentata, P. E. Mueller. 



(Plate I. Figs. 12—13.) 



Form sub-rectangular, somewhat arched above, obscurely longi- 

 tudinally striated; lower angle obtuse, margined below with short 

 setae. Post-abdomen small, slender, armed with a lateral line of 

 scales and two strong teeth at the lower angle; claw with a minute 

 basal spine. The form of the post-abdomen is identical with "Har- 

 porhynchus" falcatus, Sars, which this species also resembles in 

 having the pigment fleck larger than the eye, and in general form 

 and the character of the striation. The beak, however, is very 

 short. In size P. E. Mueller says it is among the smallest of the 

 genus. 



Sp. 12 Alona elegans, Kurz. 



(Plate I. Fig. 14.) 



Form rectangular; back slightly elevated, posterior margin high, 

 lower margin straight. Shell covered with minute striations spring- 

 ing from the region of the attachment of the head shield. Head 

 rather large, pigment fleck smaller than the eye. The antennae 

 have eight setae and a circlet of spines on the second joint of the 

 inner ramus, and a single thorn on its first joint. The post-abdo- 

 men is short and broad, rounded at the end, and is armed with 

 about ten anal teeth and a lateral row of scales. Length 0.4 mm.- 

 0.5 mm. 



Sp. 13, 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. 

 Distinguishable from the following small species in the armature 

 of the post-abdomen. 



Sp. 14. Alona spinifera, Schoedler. 



If not the young of A. affinis, this little species mimics it very 

 closely. The head is less horizontal and more acute than in that 

 species, otherwise almost identical excepting in size which is about 

 one-third. The sensory setae of the antennules are said to be nearer 

 equal. Found by Birge m Massachusetts and Wisconsin, but not 

 yet encountered in Minnesota. 



