ONCHIDIID A. 91 
Includes Onchidium, without, and Peronia (Blainv.) with rami- 
fied dorsal appendages, both of Indo-Pacific distribution ; also 
Onchidella and the doubtful genus Buchanania (Lesson). 
OnoutpiuM, Buchanan, 1800. 
Syn.—Oris, Risso ? 
Distr.—Bengal, West Indies, ete. O. typhx, Buch. (ci, 64). 
Animal limaciform, elongate-oval; tentacles wanting ; mouth 
with lobate appendages ; mantle coriaceous, tubercular, covering 
the whole back; no longitudinal furrows above the margin of 
the foot, nor caudal mucous pore; no distinct locomotive disk ; 
external respiratory orifice under the right posterior margin of 
the mantle; anal orifice separate from the last, posterior; male 
external generative orifice under the right eye-peduncle ; female 
orifice at posterior of under side of body. 
No shell or shelly plate. 
No jaw. Lingual membrane broad ; teeth different in shape 
from those of the terrestrial genera, arranged in very oblique 
rows; centrals tricuspid, side teeth all alike, bicuspid, inner 
cusp small, outer cusp larger, with greatly produced, oblique, 
squarely truncated cutting points. 
This and the three following genera are marine, and are in 
many ways distinct from the rest of the Geophila. 
In Onchidium Celticum, Cuv., the organ opening near the 
hinder end on the under side of the mantle, regarded as lungs 
by Cuvier; is really the renal organ, homologous to the organ of 
Bojanus in the bivalves; the heart is situated according to the 
type of the Opisthobranchia, and the respiratory function is 
performed by the dorsal surface of the mantle and its appen- 
dages. Consequently this species and possibly all the Onchidiid 
might well be removed from the pulmonata and placed with the 
marine slugs; which they further resemble in the larva posses- 
sing a ciliated velum and spiral shell. 
ONCHIDELLA, Gray, 1850. 
Syn.—Onchidina, Semper, 1882. 
Distr.—11 sp. European Seas, Atlantic, New Zealand. 0. 
nigricans, Quoy (cli, 68). 
Animal ovate. The respiratory orifice is placed on the right 
side of the vent, and the male orifice on the right side of the 
tentacles; whereas in Onchidium both are in the median line, 
the former behind the vent, the latter behind the tentacles; no 
dorsal eyes. Jaw thin, scarcely distinct; median tooth of the 
radula tricuspid, laterals short, oblique, bicuspid; male organs 
more simple than in Onchidium and Peronia; large glands on the 
edges of the mantle. 
Onchidella lives upon alge, and is perfectly amphibious; ex- 
