ISOPODS OF NORTH AMERICA. 



415 



which is 4 mm. in length and has the posterior margin widely rounded. 

 The terminal segment is 5 mm. wide at the base. The uropoda are 

 half as long as the terminal abdominal segment. The peduncle is 1 

 mm. long. The outer branch is 1 mm. long. The inner branch is a 

 very little longer than the outer branch. In the female the first ple- 

 o})oda are attached close together as in the preceding species. 



The first pair of legs are strongly prehensile and have the propodus 

 greatl}' dilated and the inferior margin armed with two triangular 

 processes. All the other legs are ambulatory. 



MANCASELLUS TENAX (Smith). 



Asellus tenax Smith, Ainer. Jour. Science and Arts, (3), II, 1871, pp. 453-454. 

 Asdlojisis U'liax'H.ARG Eli, Anier. Jour. Science and Arts, (3), VII, 1874, p. 601; 



Harger in Smith, Report U. S. Commissioner of Fish and Fisheries, 1874, 



pp. 659-660, pi. I, fig. 3. 

 Mancaselhis tenax Harger, Amer. Jour. Science and Arts, (3), XI, 1876, p. 304. — 



Hay, Amer. Nat., XVI, 1882, p. 242.— Underwood, Bull. 111. State Lab. 



Nat. Hist., II, 1886, p. 359. — Richardson, American Naturalist, XXXIV, 



1900, p. 297. 



Localities. — Lake Superior; Indiana; Michigan; Lake Huron. 



Bod}' oblong-ovate, a little more than two and a half times longer 

 than wide, 3 mm. : 8 mm. 



Head twice as wide as long, 1 mm. : -1 mm., with the anterior mar- 

 gin excavate on either side of a small median point. Lateral margins 

 somewhat expanded in an anterior 

 and a posterior lobe, the posterior 

 lobe being produced laterally much 

 beyond the anterior lobe. Between 

 the anterior and the posterior lobe 

 the lateral margin is slightly exca- 

 vate. The eyes are small, round, 

 composite, and situated opposite 

 the excavation a short distance 

 from the lateral margin. The tirst 

 pair of antenn.e have the tirst arti- 

 cle large and dilated; the second 

 article is half as wide as the tirst 

 article and twice as long; the third 

 article is less than half the length 

 of the second. The tiagellum is 

 composed of six articles. The tirst 

 antenna? extend to the end of the 

 fourth article of the peduncle of the second pair of antenna\ The 

 second antenna^ have the tirst three articles short and subequal; the 

 fourth is about as long as the tirst three taken together; the tifth is 

 about one and a half times longer than the fourth. The tiagellum is 

 composed of thirty articles, and extends to the posterior margin of the 



Fig. 4ii(i.— Mancasellis tknax (After 

 Hakgek). 



