[553] INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 259 
fathoms off Vineyard Sound, and has been found in the stomachs of the 
shad, mackerel, «ec. 
HETEROMYSIS FORMOSA Smith, gen. et sp. nov. (p. 396.) 
Body rather short and stout. Carapax broad behind and tapering 
anteriorly; the anterior margin produced into an obtusely triangular 
rostrum. Ocular peduncles short and thickened nearly to the base. 
Peduncle of the antennula stout, extending to the tip of the antennal 
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 flagellum stout at 
base and more than twice as long as the inner. Antennal 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; 
flagellum nearly as long as the entire body. Mandibles, maxille, first 
and second maxillipeds, as in dA/ysis. The first pair of legs (second pair 
of gnathopoda) differ remarkably from those in all the described genera 
of Myside. 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 margin; 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 
inner branch is multiarticulate as in Alysis, 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 fifth. The appendages of the first five 
segments alikein both sexes; short, rudimentary, and like the same appen- 
dages in the female A/ysis. 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 posterior margins cleft by a sinus deeper than broad, 
and armed with numerous small spines. 
