GAMMARIDiE. 
224 
A MPHTP OP A . PH OXIDES. 
NATATORIA. 
Specific character. Pereion furnished with a dorsal carina. Third seg- 
ment of the pleon having an elevation near the dorsal centre, and the 
posterior margin produced into a sharp tooth near the centre on each side. 
Length ^ inch. 
Otus carinatus. Spence Bate, Cat. Crust. Amph. Brit. Mus. p. 126, pi. 
xxiii. fig. 2. 
The head is very short, hut produced anteriorly to a 
sharp point, slightly depressed. The back is furnished 
with a small but distinct median carina. The third seg- 
ment of the tail is abruptly elevated near the middle, 
and again gradually depressed to the posterior margin. 
On each side the posterior margin is posteriorly pro- 
duced, near the centre, into a long slightly-upturned 
tooth. The eyes have not been observed. The superior 
antennse are short, being scarcely more than twice the 
length of the upper margin of the head ; the peduncle 
