S. I. Smith — Crustaceans of the Atlantic Coast. 
101 
Heteromysis. 
Heteromysis Smith, Invertebrate animals of Vineyard Sound, in Report of U. S. 
Commissioner of Fish and Fisheries, part i, p. 553 (259), 1874. 
Chiromysis G. 0. Sars. Middelhavets Mysider, Archiv for Mathematik og Naturvi- 
denskab, Kristiania, ii, p. 56 (48). pis. 19, 20. 1877. 
Professor Bars’ Chiromysis microps, described from females only, 
is unquestionably congeneric and specifically very closely allied to my 
species mentioned below. As pointed out both by Professor Sars and 
myself, the most conspicuous characteristic of the genus is in the struc- 
ture of the endognath of the second pair of gnathopods (third max- 
illipeds, or, according to Sars, first legs), which are very unlike the 
pereopods, being longer, very much stouter, with the terminal, or 
“ tarsal,” portion composed of the three normal segments, of which 
the proximal (carpus) is about as large as the preceding segment 
(merus), the two distal segments very short, the propodus being as 
broad as long and the dactylus forming a terminal claw; while the 
five pairs of pereopods are as in the genus My sis. The male affords 
additional generic characters, in having all the pleopods like those of 
the female (in which they are as in My sis ), and in having no promi- 
nently projecting sexual appendage upon the peduncles of the anten- 
nulge, but in its place only a slightly raised and nearly transverse ele- 
vation, densely clothed with hairs. 
Heteromysis formosa Smith, loc. cit. 
New Haven !, Connecticut. Tide-pool at Thimble Islands !, near 
New Haven (A. E. Verrill, 1874). Gardener’s! and Peconic ! Bays, 
1874. Vineyard Sound! and Buzzard’s Bay !, surface to 10 fathoms 
in depth, 1871, 1875. “ Among weeds, Haste Island,” Salem !, Massa- 
chusetts (J. 11. Emerton, 1878). 
Although very closely allied to the Mediterranean species, the II. 
formosa is readily distinguishable by the following characters. The 
stout carpal segment in the second pair of gnathopods, in the female, 
is armed along the distal hall' of the inner margin with six to eight 
slender spines in place of the four in II. microps , and there are in 
addition twelve to fifteen setae longer than the spines and extending 
nearly the whole length of the margin. In the male, however, this 
segment is a little more slender and has fewer spines and seta* than 
in the female. The short propodal segment, as seen in a side view, is 
nearly square, its distal margin being parallel with the proximal and 
having no angular prominence on the inner side as in II. microps. 
The inner lamella* of the uropods are nearly as long as the outer 
