118 AMERICAN MARINE CONCHOLOGY. 
tacles long, linear; branchize removed from head, arranged on 
each side in distant tufts, the last pair at extremity of tail. 
Length 6, breadth 1.2 mill. 
Massachisetts. 
Family ELYSIID. 
In this family the respiratory function appears to be performed 
by the entire surface of the body, special organs for that purpose 
being almost obsolete. 
Synopsis of Genera. 
Body with the lateral ridges dilated into wing-like natatory appendages, 
not united ; head distinct, with two conspicuous auriform tentacles. 
Enysta, Risso. 
Body with lateral lobes united together posteriorly over the back. 
ELystELua, Verrill. 
Genus ELYSIA, Risso. 
Journ. Phys., 376. 1818. 
1. E. cntorotica, Agassiz. Fig. 246. 
Gould, Invert. Mass., edit. ii. 255, t. 17, f. 251-255. 1870. 
Animal emerald-green, dotted with white and red spots; slen- 
der, tapering behind, with broad lateral expansions, folded and 
overlapping each other on the back when the animal is in motion; 
tentacles two, lanceolate, folded beneath; head distinct, obtuse, 
slightly emarginate; anterior angles of foot widely produced, 
triangular. 
Massachusetts. 
Genus ELYSIELLA, Verrill. 
Am. Journ. Sci., ser. III., iii. 288, t. 7, £ 5. 1872. 
1. E. catunus, Agassiz. Fig. 247. 
(Placobranchus.) Gould, Invert. Mass., edit. ii. 256, t. 17, f. 249, 
250. 1870. 
? Placobranchus simplex, Girard, Bost. Proc., vy. 89. 1854. 
Animal sea-green with whitish spots; body ovate-lanceolate ; 
lateral expansions two-thirds its length, not meeting when reflected 
over the back; head large, rounded, globose; tentacles short, 
blunt, broad; foot wide as body, square in front, pointed behind. 
Length 6, breadth 2.3 mill. 
Massachusetts, 
