658 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



meut is clavate; the second ou the external side gibbons, and fnrnished 

 beyond the middle with a tnft of bristly hairs ; the third slender and 

 tapering, finely and regnlarly ciliate along the external side, the cilia 

 rather suddenly increasing in length at the apex. First segment of 

 palpus of the maxilliped short ; second with the exterior margin nearly 

 straight, interior strongly rounded and densely hairy ; third subtriangular, 

 the external margin being nearly straight, the internal much curved and 

 converging toward the outer, the distal articulation of the segment being 

 less than half the length of its proximal articulation ; fourth segment 

 clavate ; fifth less than half the length of the fourth. 



First pair of thoracic legs in the male strongly chelate; the propodus 

 much enlarged and subglobular, with a prominent acute tooth, and a 

 smaller lobe on its palmary margin ; dactylus with a tubercle at the base, 

 an emargination near the middle, and a small acute spine at the end ; 

 carpus small and triangular. In the remaining pairs of legs, the carpus 

 and propodus are of about equal length and movably articulated ; the 

 posterior three are much larger than the others ; and the fourth pair 

 has a spiny tubercle on the propodus. 



First abdominal segment in the males furnished with two pairs of 

 appendages ; the outer pair composed, ou each side, of a small sub- 

 quadrate plate, to the extremity of which is articulated another some- 

 what larger plate of similar shape. The inner or upper pair composed 

 of a robust, suboval basal portion on each side, bearing at its extremity 

 two rami ; the inner ramus irregular in shape, cylindrical, bent, and 

 tapering to a blunt extremity; outer ramus biarticulate ; proximal seg- 

 ment short, expanding distally, and bearing a small, obtusely ovate 

 plate, which is ciliate near the extremity. Tlie corresponding segment 

 in the female bears a pair of short narrow plates, which meet each other 

 along their inner, straight margins, and are obliquely rounded and 

 ciliate at their extremity. Outer plates of the nest pair of abdominal 

 appendages thickened, and forming an operculum for the branchiae. 

 These opercular plates, as taken together, are orbicular in outline, and 

 broadly truncated at the end. Each plate is divided by a slightly 

 oblique suture into two unequal portions; the distal portion being about 

 twice as large as the proximal. 



Posterior pleopoda, or caudal stylets, flattened, ciliate; proximal seg- 

 ments expanded from the base, obliquely truncated at the extremity ; 

 rami narrowly ovate, pointed, the inner about twice as long as the 

 outer. The flattening of these appendages is more conspicuous in the 

 adult males. 



Length, excluding antennie and caudal stylets, 15"^°^; breadth, 5°^™. 



Above brown, spotted, and mottled with yellowish. 



This species is common under stones in streams and pools about N'ew 

 Haven, Conn. It is mentioned by Dr. Gould as common in Massachu- 

 setts in similar situations, and by Mr. Say in the neighborhood of Phil- 

 adelphia. It has also been collected, by Mr. N. Coleman, at Grand 

 Eapids, Mich. 



