104 >S'. T. Smith — Crustacemifs of the Atlantic Coast. 



length of the antemml t<cale little over six times in mixta, but about 

 ten times in stenolepis. 



The sinus of the posterior margin of the telson is much broader 

 and deeper in mixta than in stenolepis, b\it the edges of the sinus are 

 armed Avith 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 

 twenty-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 s})ines 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 diiFerence 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, aff'ords the 

 readiest means for distinguishing the two species, however. In 

 mixta there is a small arborescent sjjot of black pigment upon the 

 upper side of the last cephalothoracic segment, iipon 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 lamellae and \ipon each of 

 the first five segments of the abdomen ; there are similar but much 

 smaller spots upon the bases of the antennulje and antennje 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 antennuhe, the scales of the antennte, the dorsal sides of the eye- 

 i)eduncles, the dorsal surface of the whole abdomen, the telson, and 

 both lamella' of 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 antennulse and upon the antennal scales, all which i)arts 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 

 parts above mentioned, and is still very conspicuous in specimens 

 which have been preserved in alcohol for many years. 



This difference in the coloraticni of the two species is undoubtedly 



