GASTEROPODA. 



169 



2 principal lateral furrows, from which numerous vein-like grooves ramify ; 

 mantle not larger than the shell ; respiratory orifice on the right side, beneath 

 sub-spiral apex of the shell ; reproductive orifice behind the right tentacle. 

 The Testacella is subterranean in its habits, feeding on earth-worms, and 

 visiting the surface only at night. Its lingual membrane is very large and 

 wide, with about 50 rows of 20.20 teeth, which diminish rapidly in size to- 

 wards the centre ; each tooth is slender, barbed at the point, and slightly 

 thickened at the base, and furnished with a projection on the middle of the 

 posterior side. 



Fig. 94.* 

 Distr. 3 sp. S. Europe ; Canary Ids. Brit, (introduced.) 



FAMILY III. ONCIDIAD^E. 



Animal, slug-like, destitute of any shell, completely covered by a coriace- 

 ous mantle ; tentacles cylindrical, retractile, with eyes at their extremities ; 

 foot much narrower than the mantle. 



ONCIDIUM, Buchanan. 



Type, 0. Typhse, Buch. Etym. Diminutive of Onkos, a tubercle. 



Animal oblong, convex, usually tuberculated ; head with 2 retractile ten- 

 tacles, bearing the eyes ; mouth covered by a notched veil ; no horny jaws ; 

 tongue broad, with above 70 rows of lingual teeth (in 0. celticum}, teeth 

 54.1.54 ;f the central teeth minute, triangular, with a single obtuse spine ; 

 laterals, slightly curved ; heart opistho-branchiate ; respiratory orifice poste- 

 rior, distinct from the vent ; sexes combined, $ organ under the right ten- 

 tacle, $ at the posterior extremity of the body. 



Distr. 16 sp. Brit. Medit. Red Sea, Mauritius, Australia, Pacific. The 

 typical Onddia live on aquatic plants, in the marshes of the warmer parts ot 

 the old world. Those which frequent sea-shores have been separated under 

 the name Peronia, Bl. (Onchis, Fer). One species (0. celticum) is found 



* Part of the lingual membrane of T. halio tides, from a preparation by Fisher 

 Cocken, Esq. , of Botesdale. The dentition resembles that of lanthina. 



t This is a convenient mode of stating the number of lingual teeth in each row; 

 it means that there is a single (symmetrical) tooth in the centre, and 54 lateral (un- 

 - symmetrical) teeth on each side. If the number of rows of teeth on the dental mem- 

 brane is known, it may be added below, thus Peronia Mauritiana, -- 



