APPENDIX, 501 
AMPHIPODA., LYSIA NASSIDES. 
NATATORLA, (Vol. I. p. 118.*) 

Genus—OPIS. (Avoyer.) 
Generic character. Resembles Anonyx, with the exception that 
the first pair of gnathopoda have the inferior angle of the propodos 
considerably produced, so that the hand is formed into a didactyle 
chela. ‘ 

OPIS LEPTOCHELA, N.S. 
Specific character. Upper antenne with the two basal joints large ; lower 
antenne half as long again as the upper. Both pairs of gnathopoda minute, 
slender, and subequal. 
Length, about one-fourth of an inch. 
Tue cephalon is small, not produced anteriorly. The 
segments of the pereion and pleon are dorsally subequal in 
length ; the fourth segment of the pleon having a deep notch on 
the dorsal surface. The eyes are small and round. The first 
two joints of the superior antenne large ; the flagellum short ; 
secondary appendage short. The inferior antennze are slender, 
being half as long again as the superior. Cox deep. Gnatho- 
