78 S. I. Smith — Crustaceans of the Atlantic Coast. 
10’5 to i7 mm in length, and the females from 13 to 23 mm ) had either 
three or four teeth on the dorsal edge of the rostrum, and none at 
the tip or beneath ; and this is evidently the normal rostral dentition 
of the species, although the fourteen remaining specimens show con- 
siderable deviation from this typical form. Of these fourteen speci- 
mens, nine) all females from off Nantucket, from the Bay of Fundy, 
and from Halifax, Nova Scotia, and varying from 19 to 25 mm in 
length), have four teeth above and one beneath the tip, and three of 
these nine, all females from the Bay of Fundy, and each about 
23 mm in length, have the inferior tooth so near the tip that the tip is 
best described as bifid; one female, 22 mm long, from the Bay of 
Fundy, is similarly armed at the tip but has only three teeth above; 
one female, 16 mm long, from Halifax, Nova Scotia, has five distinct 
teeth above but none below; while three males, 12 to 13*5 mm long, 
from Casco Bay and Caslie’s Ledge, have only two teeth above. 
This would seem to show that a tendency to an increase in the 
number of rostral teeth is characteristic of the females, while the 
reverse is the case in respect to the males. 
The usually very constant arrangement of the terminal spines of 
the telson is occasionally subject to variation, which apparently fol- 
lows the same tendency in the sexes as the variation in the number 
of rostral teeth, although the number of observations in either case is 
too small for a reliable generalization. Of forty-eight specimens in 
which the tip of the telson was specially examined, forty-five (among 
which the males varied from 12 to l7 mm in length, and the females 
from 14 to 25 mm ), had the normal number of terminal spines; that is, 
a short one at the lateral angle each side, two much longer ciliated 
ones in the middle, and, between these and the lateral spines each 
side, a still longer and stouter spine, making six in all (Plate IX, 
figure 7). Of the remaining specimens, a male i7 ,nm long, from the 
Bay of Fundy, has but one median ciliated spine, so that there are 
only five in all (Plate IX, figure 6) ; and yet there is not the slightest 
appearance of this irregularity being due to injury, and the specimen 
is in all other respects perfectly normal. A female 20 - 5 mm long, from 
the Bay of Fundy, has nine spines, of which the three median are 
ciliated (Plate IX, figure 4) ; there is a little irregularity in the 
spines, apparently due to some slight injury. Another female 16 mm 
long, from Halifax, Nova Scotia, has also nine spines, of which the 
five central ones were probably ciliated, although, apparently on 
account of the imperfect state of preservation of the specimen, I was 
able to discover cilia on only a part of them, as shown in the figure 
