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. 
* Diaptomus sanguineus Forbes. 
PLATES V, Fras. 8, 9; XIII, Fie. 12. 
Forbes ’76; Herrick ’83 and ’84; De Guerne 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. First segment of abdomen long, armed 
with strong lateral spines. Second segment very short. Caudal stylets 
rather longer than broad, ciliated, setze short. The antennz 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 occupies 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 
as1.8mm. 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. 
* Diaptomus minnetonka Herrick. 
PLATE XIII, Fies. 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 
