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inner, and both tipped with a brush of long hairs, and fringed with numer- 
ous setite : as are also the margins of the peduncle 
Caudal stylets of the female only two- thirds the length of the abdo- 
men, peduncle wider proportionally than in the male, and obtriangular. 
Rami more lanceolate in outline, scarcely a fourth as wide as long ; the 
outer nearly as long as the inner, which is nearly a third longer than the 
peduncle. 
Found in large numbers in shallow pools of a slow prairie stream, near 
Abingdon, Knox county, Illinois. 
This fine large species is probably nearly related to Asellus intermedins, 
Forbes. It differs, however, from all the forms of this that I have seen, 
not only in its much greater size, but also in some other important respects. 
The head is much narrower in the present species than in intermedins. The 
abdomen is narrower in this than the species described by Prof. Forbes, as 
compared with the width of the thoracic segments. The thoracic segments 
in specimens of undoubted intermedins which I have, increase in width from 
the first to the last, while in A. militaris they are, after the second, of uni- 
form width. The two posterior segments in A . militaris are also much more 
deeply concave along their posterior margin than in the other species men- 
tioned. The propodus in the present species is broader than in intermedins, 
but I have specimens of an Asellus from Prof. Forbes, which he provisionally 
regards as A. intermedius, in which the propodus is rather broader than in 
my species. The genital plates, however, differ much from those of A. mil- 
itaris . The plates, again, are, in militaris , almost exactly as in the typical 
specimens of intermedius. The doubtful forms of intemedius , however, differ 
from the present species in the width of head, abdomen, concavity of pos- 
terior thoracic segments and in the form of the caudal stylets. 
My thanks are due Prof. Forbes for specimens of his two forms of A. 
intermedius and for the use of microscope slides. 
