362 LOPHOCERCID®. 
‘BULLOPsiISs, Conr.. Like Hydatina with a depressed spire and 
inflated body-whorl, inner lip with two close folds. B. cretacea, 
Conr. Cretaceous; Mississippi. 
Erationta, Deshayes, 1864. 
Liym.— Dedicated to M. Etallon, a French paleontologist. 
Distr.—3 sp: Eocene; Paris basin, Valognes. HH. prisca, 
Desh. (lxxxviii, 62). 
Shell ovate, subfusiform, resembling certain small Mitres; 
spire short, conical, obtuse, few-whorled; aperture elongated, 
narrow, base entire, subemarginate; lip simple, acute, arched ; 
columella thick, cylindrical, twisted in the middle to resemble 
an obtuse plait ; acute anteriorly. 
Famity LOPHOCERCID A. 
Shell spiral, very thin, subflexible, with epidermis. 
Head with two ear-like tentacles; eyes sessile on the sides of 
the head; gill regular, pectinate; organs of generation close 
together in one tubercle; male organ on the right side of the 
nape near the tentacle. ‘In Lophocercus, the body is covered 
with papilla, and produced behind into a long, pointed tail ; foot 
with the natatory appendages undivided, reflexed and partly 
covering the shell in front and united posteriorly. 
Lopuocercus, Krohn. 
Syn.—Icarus, Forbes. Oxynoé, Raf. 
Eaample.—L. Sieboldi, Krohn (1xxxix, 68, 70°. 
Shell like Bullea; convoluted, thin, ovate, covered with epi- 
dermis, outer lip separated at the suture, posterior angle inflected 
and rounded. 
Animal slender, papillose ; tentacles 2, ear-shaped ; eyes sessile 
on sides of head; side-lobes reflected and partly eoYering the 
shell, united behind ; tail long and pointed. 
VOLVATELLA, Pease. Shell resembling Lophocercus, but more 
convolute. Foot small, mantle concealed, vent posterior, eyes 
concealed in the fold of the sides of the head... D fragilis, 
Pease. 
AKERA, Muller. 
Etym.—Akeros, hornless. ] 
Distr.—i sp. Greenland, Great Britain, Mediterranean, East 
Indies, New Zealand. A. soluta, Chemn, (I1xxxix, 63). Fossil. 
Eocene. 
Shell thin, flexible, globosely cylindrical, spire truncated, 
whorls channeled ; aperture long, expanded and deeply sinuated 
in front, outer margin disunited at the suture; columella open, 
exposing the whorls. 
Head-disk greatly elongated, wide and_ bifid anteriorly, and 
