ENTOMOSTRACA OF MINNESOTA. 71 



segment than the base and is weak and short. The outer ramus of 

 the left foot has a cushion of small spines and two small teeth at the 

 apex and a ciliate lamina along its inner aspect. The inner ramus 

 of this leg is nearly as long as the outer. 



* Diaptoinus saiiguiueus Forbes. 



Plates V. Figs. 8, 9; XIII, Fig. 12. 



Forbes '76; Herrick '83 and '84; De Gueine and Richard '89; Marsh '93. 



A compact species, usually brilliantly colored. Greatest width in 

 front of but near the middle of the cephalothorax. Last segment of 

 thorax laterally produced and armed with two strong spines and pro- 

 duced or "humped" dorsally. Firstsegment of abdomen long, armed 

 with strong lateral spines. Second segment very short. Caudal stylets 

 rather longer than broad, ciliated, setse short. The antennae reflexed 

 nearly reach the stylets. The right male antenna is strongly genicu- 

 late and its antepenultimate segment is armed with a hyaline lamella 

 forming a short hook apically. The right foot of the male is remark- 

 able for the thick segment bearing the two rami, the outer of which is 

 rather long. The terminal claw is rather short and not strongly 

 curved, and seems at times to be crenulately toothed near the apex. 

 The accessory spine is a little beyond the middle of the second seg- 

 ment of the outer ramus, of which the proximal segment is very small. 

 The inner ramus is short and unarmed (it is incorrectly represented 

 by Forbes as being on the outer aspect), and on the outer aspect is a 

 long spine larger than the ramus, but not jointed, beneath which is 

 an accessory spine or bristle. The left foot is very short and compact 

 — "fleshy" is a suggestive word. The inner ramus is short and un- 

 armed, while a strong spine occuj)ies the corresponding position ex- 

 ternally. The apical segment bears a stout claw externally and a 

 smaller opposable spine internally. The species is quite variable. 

 Individuals from very stagnant water may reach 2.0 mm , while 

 others in clear pools do not exceed 1.7 mm. The mean may be taken 

 as 1.8 mm. The curious fact that there is a succession in rain pools 

 in spring beginning with D. stagnalis and passing through several 

 varieties to D. sanguineus later in the season, has led the writer to 

 suspect an actual transition. Of the heterogenetic character of these 

 forms there is absolute proof as in Cyclops, but much farther study is 

 necessary to clear up the most interesting biological laws involved in 

 the distribution of these species. 



* Diaptoinus iniunetoiika Herrick. 



Plate XIII, Figs. 8-10. 



Herrick '84; De Guerne and Richard '89; Marsh '92. 



We are inclined to agree with Marsh that this form is but one of 



the many variations of D. sanguineus. Besides being somewhat smaller 



than D. sanguineus the species differs from it in minor details of the 



