84 
S. I. Smith — Crustaceans of the Atlantic Coast. 
Males when not more than 25 mm 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 mm in length, if not 
earlier, since two specimens which I have examined, 34 and 37 mw 
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 Ium in length. These four, the only specimens seen with eggs, 
were all taken in 16 to 100 fathoms, at and off 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 conspicuous that 
they afford 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 
lamellae are furnished with long plumose setae 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 setae or slender 
spinules, but entirely want the long plumose setae 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 lamellae, which are narrowly ovate, 
and margined with long, plumose setae in both sexes, but in the 
female there is, arising from the proximal half of the inner margin, 
