ISOPODS OF NORTH AMERICA. 



423 



*! $//'. 

 <^\i$i^"- f 



just below the anterior lobe. The sixth and seventh segments have the 

 posterior part of the lateral margin excavate, the anterior part pro- 

 jecting in a large lobe, and the epimera large and conspicuous and pos- 

 teriorly situated just below the middle of the lateral margin. 



The abdomen is composed of two short segments followed by a large 

 terminal segment, which has a 

 large rounded median lobe on 

 the posterior margin between 

 theuropoda. The uropoda are 

 as long as the terminal abdom- 

 inal segment. The outer branch 

 is as long as the peduncle. The 

 inner branch is one and one- 

 third times longer than the outer 

 branch. 



The first pair of legs are sub- 

 chelate, and have the propodus 

 armed on the inferior margin 

 with a triangular process about 

 the middle, and below this a strong conspicuous spine. The inferior 

 margin of the dactylus is furnished with a row of numerous short 

 spines. All the other pairs of legs are ambulatory. 



The types of this species from which the above description is made 

 were sent to me from the Museum of Comparative Zoology of Har- 

 vard University. 



Specimens collected in the Potomac River near Wasnington of the 

 same or perhaps a closely related species differ onh r in their larger 

 size, being -i mm. : 11 mm. ; in having three mo re. articles in the flagel- 

 lum of the first antennae, the flagellum of the second antenna? having 

 also a larger number of articles, sixty-three altogether, and in having 

 the uropoda equal to two-thirds the length of the terminal segment. 



Fl'i. 476. ASELLUS INTERMEDIUS (AKTEK FORBES). 



n, ONE OF FIRST PAIR OF GENITAL PLATES OF 

 MALE, x 51. b, ONE OF SECOND PAIR OF GENITAL 



PLATES OF MALE. X 51. 



ASELLUS BREVICAUDA Forbes. 



Asellus br-evicauda FORBES, Bull. 111. Museum Nat. Hist., No. 1, 1876, pp. 8-10. 

 I'XDERWOOD, Bull. 111. State Lab. Nat. Hist., II, 1886, p. 359. RICHARDSON, 

 American Naturalist, XXXIV, 1900, p. 297. 



Localities. Found in clear, rocky rills in Jackson and Union coun- 

 ties, in southern Illinois; small creek emptying into Redfoot Lake, 

 Tennessee. 



Body oblong-ovate, three times longer than wide, 4 mm.: 12 mm. 



Head more than twice as wide as long, 1 mm. : 2 mm. , with the 

 anterior margin excavate and the antero-lateral angles somewhat 

 truncate. The eyes are small, round, composite, and situated at the 



