No. 26.] ARTHROSTRACA OF CONNECTICUT. I7I 



number of strong ciliated setas. Posterior segments of abdomen 

 flattened and sometimes fused. 



Antennas unequal; first pair slender, without accessory flagel- 

 lum but with principal one multiarticulate. Second antennae 

 strong, pediform, generally much stronger in male than female; 

 fourth joint of peduncle large and produced distally to a spini- 

 form process ; fiagellum short, triarticulate, terminating in several 

 small hooks. 



Mandibles with palp small and narrow, composed of only 

 two joints. First maxillae with inner plate obsolete. Second 

 maxillae with outer lobe larger than inner. Maxillipeds with 

 inner plates narrowly produced; outer plates long and narrow; 

 palp slender, with fourth joint short and setose at tip. 



First gnathopods slender with ischium forming below a 

 rounded, densely setose expansion, carpus much elongated and 

 densely setose behind, propodus narrow, with short palm. Second 

 gnathopods somewhat stronger than first ; merus forming a broad 

 lamellar expansion which is firmly connected with posterior 

 margin of carpus, and edged with a double row, of extremely 

 elongated and finely ciliated setje ; propodus sublinear, without 

 distinct palm. First two pairs of pereiopods with basal joint 

 large and broad and merus more or less expanded. The two 

 succeeding pairs comparatively stout and of same structure, both 

 having merus obliquely expanded in front and carpus armed 

 with two oblique rows of strong spines. Last pair of pereiopods 

 elongated and slender with basal joint expanded and densely 

 fringed with long ciliated setae on both margins. 



First and second uropods with short rami; last pair with 

 peduncle scarcely expanded, and single ramus lamellar and 

 setose. Telson small, entire. 



Corophium cylindricum (Say). 



1818. Podocents cylindricns, Say, Jour. Acad. Nat. Scl. 

 Phila., vol. I, pt. 2, p. 387. 



1874. Corophium cylindricum, Smith, Rep. U. S. Com. Fish., 

 1871-2, p. 566. 



Body broad and much depressed, with very small coxal 

 plates which are discontinuous. Fourth, fifth, and sixth abdom- 

 inal segments fused. 



