ENTOMOSTRACA OF MINNESOTA. 215 



the posterior margin has a series of long sharp teeth; the mandibles 

 are nearly completely exposed by the arched anterior margin of the 

 valves. 



The labrum, in this species, is an odd link between that of the 

 l)o[>Jtnida: and Lynceidw. The basal segment is greatly enlarged and is 

 snb-triangnlar in outline, with a movable lip attached to the inner 

 free face; the typical daphnoid structure is preserved, but the enlarged 

 salient angle of the basal portion shows how the transition to the great 

 triangular labrum of Alona, etc., is made. In young specimens the 

 head is proportionately larger, the antennules are broader at the tip, 

 and the dorsal outline is less convex; the marginal spines of the valves 

 are also proportionally larger, as are the appendages of the first and 

 last pairs of feet. This is one of the largest species of the genus, 0.75 

 mm. being the length. This is very close to M. rosea but seems 

 distinct. 



This form is quite commom about Minneapolis, Minn., but is not 

 yet noted elsewhere in America. 



*Macrothrix i>aui)er Herrick. 

 Plate LVI, Fig. 4. 



This species is described from a single specimen from Lake Minne- 

 tonka, and I can add nothing to the very meager notice given then. 

 (Herrick '82.) 



The body is broad and very narrow, the lower outline is angled 

 and nearly unarmed; the pigment fleck and eye are small and approxi- 

 mated; antennules very long and cui-ved backward and outward; ab- 

 domen short, ciliate below; claws short, ciliated. This female had a 

 full complement of eggs but the antennae resemble those of a male. 

 This is unusually interesting and should be rediscovered and studied; 

 for there seems to be some affinity between this species and Bosmina, 

 and it is probable that it requires to be distinguished generically from 

 Macrothnx. 



GENUS LITHONURA Lilljeborg. 



The form is oval; the head is curved more than in Macrothrix and 

 the shell is more obtuse behind, sinuate below where it is beset with 

 short spines anteriorly; first antennae long, straight; second antennae 

 with five setoe on each ramus; only four pairs of feet apparent; ab- 

 domen short, prolonged upward to the insertion of the caudal stylet; 

 male similar but smaller. 



