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 Fislieries, part i, p. 553 (259), 1874. 

 Chiromysis G. 0. Sars, Middelliavets Mysider. Archiv for Mathematik og Naturvi- 



denskab, Kristiania, ii. p. 56 (48), pis. 19, 20. 1877. 



Professor Sars' Chiromysis uuerops, desci-ibed 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 Avhich 

 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 Mysis), and in having no jDromi- 

 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, loe. eit. 



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, 1 875. " Among Aveeds, Haste Island," Salem !, Massa- 

 chusetts (J. H. Emerton, 1878). 



Although very closely allied to the Mediterranean species, the IT. 

 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 seta? 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 If. microps. 

 The inner lamella^ of the uropods are nearly as long as the outer 



