92 ORDERS AND FAMILIES. 



PYRAMIDELLID^;. Shell small, conical, turreted, apical whorls sinistral ; 

 mouth small, angulated, channelled, outer lip thin ; operculum horny, 

 ear-shaped, nucleus excentrical. Odostomia, 468 to 502. 



RISSOID^E. Shell small, oblong or oval, white or horny ; spire usually 

 long ; mouth oval or trumpet-shaped, angulated above and slightly 

 expanded below ; operculum horny. Rissoa, 400 to 424. 



SCALARIID.'E. Shell long, turreted, with transverse ribs; mouth round; 

 operculum horny and few whorled. Scalaria, 360 to 364 ; Aclis, 

 365 to 369. 



SKENEID^E. Shell small, circular; spire much depressed or involute; 

 mouth round; operculum horny, round and spiral. Skenea, 434. 



TRICHOTROPID^. Shell conical, last whorl large ; spire erect ; mouth 

 grooved within at the base ; operculum blunt and claw-shaped. 

 Trichotropis, 380 ; Torellia, 381. 



TRITONID^. Shell thick, outer lip inflected and thickened ; whorls 

 strengthened lengthwise by varicose ribs; spire bluntly pointed; 

 outer lip and pillar folded or tuberculate ; canal straight ; operculum 

 horny, nucleus at outer base of mouth. Triton, 459, 460. 



TROCHID^;. Shell nacreous, pyramidal with a nearly flat base, whorls 

 many, flat and striated; pillar twisted; operculum horny. Trochiis, 

 338 to 354. 



TRUNCATELLID^E. Shell cylindrical, minute; spire truncated, whorls 

 striated transversely ; mouth oval ; operculum horny, sub-spiral, ear- 

 shaped. Truncatella, 399. 



TURBINIDJE. Shell bulimoid, polished, richly coloured; whorls convex; 

 mouth oval, not pearly; operculum shelly. Phasianella, 355. 



TURRITELLIDJE. Shell pyramidal and long, upper part divided off when 

 disused ; whorls many, slowly enlarging, spirally ribbsd or striated; 

 mouth small, round or inclined to be square ; operculum horny, 

 rather solid, puckered obliquely, nucleus central. Turritella, 452. 



VALVATID^;. Shell turbinate or discoidal ; spire short and symmetrical; 

 mouth rounded and entire ; umbilicated ; operculated ; operculum 

 horny, nucleus central. Valvata, 441, 442. 



VIVIPARID^;. Shell turbinate with long symmetrical spire, whorls rounded, 

 mouth oval, operculum horny and irregularly concentric. Vivipams, 

 439, 440. 



ProtObranehiata. (PELECYPODA.) Plate i. Nos. i to 8. 



. Gills small ; labial pulpi very large ; mantle free all round ; 

 foot long ; shell like a small nut with many serrate teeth, often with 

 posterior side produced. Genera, Nucula, i to 4 ; and Leda, 5 to 8. 



