ORDERS AND FAMILIES. 93 



Pseudolamellibranehiata. (PELECYPODA.) Plates iii. to v. 



Nos. 30 to 48. 



AVICULID^E. Shell oblique and winged; with long straight dorsal margin; 

 posterior adductor nearly central ; anterior adductor, when present, 

 leaving impression within the beak. Avicula, 30 ; Pinna, 31. 



LIMID^E. Shell nearly equivalve, eared; cartilage external; muscular 

 scar on one side. Lima, 44 to 48. 



OSTREID^;. Shell irregular, attached by the left valve; a single adductor; 

 hinge without teeth ; margins occasionally notched ; cartilage internal 

 and horizontal on the hinge line; no foot; mantle lobes free all round. 

 Ostrea, 32. 



. Shell equilateral, with unequal wings at beak ; inequivalve ; 

 some with the right valve convex and the left flat ; cartilage internal 

 and in a cavity beneath the beaks. Pecten, 33 to 43. 



Pulmonata. (GASTROPODA.) Plate xvii. to xx. Nos. 201 to 318. 



AURICOLID^E. Shell spiral, conoidal ; mouth toothed; umbilicus indistinct 

 or absent ; tentacles two, not retractile, eyes generally at base. 

 Carychium, 201 ; Melampus, 202, 203. 



HELICID;E. Animal terrestrial ; shell spiral, globose or coil-shaped ; with 

 or without umbilicus ; tentacles four, retractile ; eyes at the tip of 

 the upper pair which are the longer. Vitrina, 247 ; Zonites, 248 to 

 258 ; Bulimus, 259 to 262 ; Helix, 263 to 287. 



Animal terrestrial ; shell internal, placed beneath the mantle, 

 rudimentary or shield shaped ; tentacles four, cylindrical, retractile ; 

 eyes at the tip of the dorsal pair. Amalia, 232, 233 ; Limax, 234 to 

 240 ; Avion, 241 to 245 ; Geomalacus, 246. 



. Shell spiral, hood-shaped, or coil-shaped; thin; horn- 

 coloured ; mouth without teeth, lip sharp ; pulmonary sac protected 

 by an external lobe ; tentacles two, not retractile ; eyes at base. 

 Ancylus, 205, 206 ; Limn#a, 207 to 214 ; Planorbis, 215 to 226. 



ONCHIDIID^E. No shell; animal oval and slug-like; two tentacles, 

 retractile, with eyes at their tips ; a thick mantle over the dorsal 

 region, covered with tubercles, having eyes identical in type with 

 those of the vertebrata ; foot much narrower than mantle. Onchidium, 

 318. 



OTINID^. Shell ear-shaped and minute, spire short, apex introverted, 

 mouth large, outer lip plain and sharp, no operculum ; tentacles two, 

 not retractile ; eyes at base. Otina, 204. 



PHYSIOS. Shell sinistral, lustrous, thin, without operculum ; mantle 

 covering part of the shell ; tentacles two, not retractile ; eyes at base. 

 Physa, 227 to 229. 



PUPID.E. Shell cylindrical or oblong, occasionally furnished with internal 

 lamellae ; many narrow whorls, last whorl no broader than the pre- 

 ceding ; mouth generally with one or more teeth. Pupa, 288 to 291 ; 

 Vertigo, 292 to 302 ; Balea, 303 ; Clausilia, 304 to 309 ; Cochlicopa, 

 310, 311. 



