104 
S. I. Smith — Crustaceans of the Atlantic Coast. 
length of the antennal scale little over six times in mixta , hut about 
ten times in stenolepis. 
The sinus of the posterior margin of the telson is much broader 
and deeper in mixta than in stenolepis , but the edges of the sinus are 
armed with fully as many spines in stenolepis , so that they are much 
more closely crowded. The spines of the lateral margins of the tel- 
son are fewer and rather larger in stenolepis (there are usually 
twentv-four or twenty-five spines each side in the adult stenolepis , 
and over thirty in mixta ) and do not extend to so near the tip, the 
most posterior spines in stenolepis arising very little if at all back of 
the bottom of the sinus of the posterior margin, while in mixta there 
are at least three or four spines arising back of the bottom of the 
sinus. A part of this last difference is due to the greater depth of 
the sinus in mixta , but the terminal portion of the margin back of 
the spines is absolutely fully twice as long in stenolepis as in mixta. 
The coloration, even in ordinary alcoholic specimens, affords the 
readiest means for distinguishing the two species, however. In 
mixta there is a small arborescent spot of black pigment upon the 
upper side of the last cephalothoracic segment, upon each of the seg- 
ments of the abdomen except the sixth, one each side at the base of 
the telson, and beneath upon the ovigerous lamella? and upon each of 
the first five segments of the abdomen ; there are similar but much 
smaller spots upon the bases of the antennulae and antennte and 
usually two minute ones on the distal half of the antennal scales; 
but with the exception of these pigment spots and the eyes, the 
entire animal is opaque white, turning to grayish white in alcohol. 
In specimens which have been preserved in alcohol for a very long 
time, the pigment spots often become obscure or wholly obliterated. 
In stenolepis , on the other hand, the peduncles and inner flagella of 
the antennulse, the scales of the antennae, the dorsal sides of the eye- 
peduncles, the dorsal surface of the whole abdomen, the telson, and 
both lamellae ol the uropods are covered with widely and thickly 
branching ramifications of numerous large pigment spots. The color 
is particularly conspicuous upon the peduncles and inner flagella of 
the antennulae and upon the antennal scales, all which parts of the 
animal appear very dark or often almost black. There is considera- 
ble variation in the amount of pigment in different individuals, but 
in all the specimens examined it is invariably present upon all the 
pails above mentioned, and is still very conspicuous in specimens 
which have been preserved in alcohol for many years. 
This difference in the coloration of the two species is undoubtedlv 
