HIGHER CRUSTACEA OF NEW YORK CITY 



161 



A fresh-water form with accessory flagellum on antenrmlae, and 

 gnathopoda of moderate size in both sexes. 



These two points are enough to distinguish this species from the 

 only other fresh- water Amphipod, A 1 1 o r c h e s t e s d e n t a t a . 

 In addition, the last three segments of the abdomen are armed with 

 median and lateral fascicles of spines, and the terminal uropoda 

 are long and fringed with hairs. Length 10-15 mm. Color white 

 with green markings. 



Common in fresh-water ponds among the weeds, and in the brooks 

 under stones. 



Carinogammarus mucronatus (Say) 



Gammams mucronatus Say, T. /. c. 1818. 1:376. DcKay. /. c. 

 1844. p.37. Verrill. /. c. 1874. p.559. 



Fig. 30 Carinogammarus mucronatus 



First three abdominal segments produced dorsally into acute teeth. 



The above character will distinguish the present species from all 

 of our other common Amphipoda. The antennulae are about 

 equal in length to the antennae. Gnathopoda of moderate size in 

 both sexes. Lower posterior angle of first three abdominal seg- 

 ments produced and last three furnished dorsally with median and 

 lateral fascicles of spines. 



