84 S. I. Smith — Crustaceans of the Atlantic Coast. 



Males Avhen not more than 25'""' in length show distinctly the sex- 

 ual characters in the first and second pairs of abdominal legs, and 

 they arrive at sexual maturity at a little over 30""" in length, if not 

 earlier, since two specimens which I have examined, 34 and 37""" 

 long, have the sperm ducts, or spermatophores extruded, — probably 

 a result of the contraction due to the preservation of the specimens in 

 alcohol. Among four females carrying eggs the smallest is about 

 40""" in length. These four, the only specimens seen with eggs, 

 Avere all taken in 16 to 100 fathoms, at and oif Halifax, Nova Scotia, 

 September 4, 5, 6, 1877. 



Since some, even recent, authors have apparently had difficulty in 

 distinguishing with certainty the sexes in the species of Hippolyte, I 

 introduce figures of the first pair of abdominal appendages and of the 

 inner lamella of the second pair in the male and female of this species, 

 to illustrate the sexual differences in these appendages in the genus. 

 (Plate XI ; figure 1, appendage of the left side of the first segment of 

 the male; figure 3, corresponding appendage of the female; figure 2, 

 inner lamella of the appendage of the left side of the second segment 

 of the male ; figure 4, corresponding part of the appendage of the 

 female). At least in all the species of Hippolyte mentioned in this 

 paper, the differences in these appendages in the two sexes are very 

 similar to those shown in these figures, and are so couspicuous that 

 they aftbrd the readiest means for distinguishing the sexes, which is 

 easily done at a glance. 



In the first pair of abdominal appendages of the female, both 

 lamella are furnished with long plumose set® upon each margin to 

 the very tip, as in the succeeding appendages; the outer lamella is 

 always much narrower than the more or less ovate inner one and is 

 linear in outline. In the male the basal portion of the appendage is 

 relatively smaller than in the female ; the outer lamella is similar to 

 that in the female, but very much larger, and even larger than the 

 inner lamella in the male ; this inner lamella always tapers rapidly 

 into a slender terminal portion which is naked, except a few minute, 

 very short, modified and hook-like spines at the very tip ; the margins 

 toward the base, however, are furnished with short sette or slender 

 spinules, but entirely want the long plumose seta^ so characteristic of 

 the corresponding parts of the other appendages. 



In the second pair of abdominal appendages, the differences are 

 mostly confined to the inner lamellie, which are narrowly ovate, 

 and margined with long, plumose seta? in both sexes, but in the 

 female there is, arising from the proximal half of the inner margin, 



