No. 415.] MWORTH-AMERICAN INVERTEBRATES. 589 
otocysts symmetrically distributed about the margin, between the tentacular 
bases; manubrium large and long, extending beyond the velum, and ter- 
minating in a series of fringed, lip-like lobes. Hydroid (?). 
Obelia Per. & Les. 
Generic characters: Medusa flat and disk-like; marginal tentacles 
numerous, projecting slightly inward at the base; otocysts eight, borne on 
base of tentacles at the inner portion; manu- 
brium short and somewhat quadrate. Medusz 
often swimming with everted bell. 
O. geniculata Linn. (FIG. 55). 
Medusa flat ; marginal tentacles twenty-four 
at liberation; gonads as oval bodies beneath 
middle of radial‘canals. Hydroid, — /dzd. 
O. longissima Pallas. 
Fic. 55. — Obelia geniculata Linn. 
Very similar to preceding. Hydroid, — /ézd. 
O. flabellata Hincks. 
(Eucope polygena A, Ag.) 
In general aspects indistinguishable from the preceding species. Hydroid, 
— Lbid. 
O. gelatinosa Pallas. 
(Laomedia gigantea A. Ag.) 
In general feature similar to former, but with only sixteen tentacles at 
liberation. Hydroid, — Jdzd. 
O. dichotoma Vinn. 
Indistinguishable from O. gelatinosa. Hydroid, — fbzd. 
O. commisuralis McCr. 
In general features very like the preceding species, but with tentacles 
somewhat more slender and elongated. Hydroid,— /ézd. 
Tiaropsis diademata Ag. (FIG. 56). 
Medusa ovoid when young, becoming hemispherical at maturity ; radial 
canals four ; marginal tentacles very numerous, the larger with swollen bulbous 
bases ; otocysts eight, situated between bases of tentacles and with otoliths 
in form of arc; gonads extending beneath radial canals; manubrium short, 
with terminal lobes complexly fimbriated. Hydroid (?). 
