ONCHIDIID^. 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). 



Onchidium, Buchanan, 1800. 



Syn — Oris, Risso ? 



Distr. — Bengal, West Indies, etc. 0. typhse^ Buch. (ci, 64). 



Animal liraaciform, elongate-oval ; tentacles wanting ; moutli 

 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 difi"erent 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 thi'ee followino- s-enera are marine, and are in 

 many ways distinct from the rest of the Greophila. 



In Onchidium Gelticum, 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. Consequentl}^ this species and possibly all the Onchidiidje 

 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. — II sp. Euroi^ean Seas, Atlantic, New Zealand. 0. 

 nigricans, Ql^oy (cii, 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 algse, and is perfectly amphibious ; ex- 



