INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 553 



fathoms off Vineyard Sound, and has been found in tbe stomachs of the 

 shad, mackerel, &c. 



HETER03IYSIS F0R3I0SA Smith, gen. et sp. nov. (p. 390.) 



Body rather short and stout. Carapax broad behind and tapering- 

 anteriorly ; the anterior margin produced into an obtuselj^ triangular 

 rostrum. Ocular peduncles short and thickened nearly to the base. 

 Peduncle of the antennula stout, extending to the tip of the autennal 

 scale; the terminal segment in the male wanting the usual elongated 

 sexual process, but having in its place a very dense tuft of long hairs ; 

 inner flagellum nearly as long as the carapax; outer tlagellum stout at 

 base and more than twice as long as the inner. Autennal scale about 

 three and a half times as long as broad, not quite reaching to the ex- 

 tremity of the peduncle of the antennula, ovate, obtuse at the tip, ex- 

 ternal margin without a spine and ciliated like the inner; peduncle 

 elongated, penultimate segment considerably longer than the ultimate j 

 tlagellum nearly as long as the entire body. Mandibles, maxilloe, first 

 and second maxillipeds, as in Mysis. The first pair of legs (second pair 

 of gnathopoda) differ remarkably from those in all the described genera 

 of Mysidiie. The whole leg is stouter than in the succeeding pairs, and 

 the terminal portion, corresponding to the multiarticulate portion of the 

 inner branch (endopodus) in Mysis, &c., consists of only three segments 

 including the terminal claw; the first of these segments is stout, slightly 

 shorter than the preceding (meral) segment, and armed with stout 

 spines along the distal portion of the inner margiu ; the second seg- 

 ment is very short, not longer than broad, and closely articulated to the 

 preceding segment so as to admit of very little motion ; the ultimate 

 article is a long, slightly curved claw, freely articulated to the preceding 

 segment. In the five posterior pairs of legs the terminal portion of the 

 i inner branch is multiarticulate as in Mysls, in the first composed of five 

 segments, besides a stout terminal claw like that in the preceding pair, 

 and in the four remaining pairs of six segments and a slender terminal 

 claw. The exopodal branches of all the legs are well developed. 



Abdomen a little more than twice as long as the carapax, the sixth 

 segment a little longer than the fiftii. The appendages of the first five 

 segments alike in both sexes ; short, rudimentary, and like the same appen- 

 dages in the female Mysis. Inner lamella of the sixth segment projecting 

 very slightly beyond the extremity of the telson, broad, ovate; outer 

 lamella only a little longer than the inner, about two-sevenths as long 

 as broad, inner margin quite convex, outer very slightly, tip rounded. 

 Telson short, broad at base, and narrowed rapidly toward the extremity, 

 the width at base about two-thirds the length, at the extremity only a 

 third as wide as at base ; the lateral margins each armed with twelve 

 to fourteen spines, which increase in size distally, and a very long ter- 

 minal spine; the jiosterior margins cleft by a sinus deeper than broad„ 

 and armed with numerous small spines. 



