GENUS XXVII. TROCHVS. 123 



Linnaeus describes 26 species, Gnielin has added 98, and 



Dr. Turton 10. Total, 134. 



Lamarck has divided this genus into five, as follow^ : 



Trochus. Shell conic, with a transversely depressed and 

 nearly quadrangular aperture, and an oblique axis (see 

 T. niloticus, pi 7. /. 93). 



Solarium. Shell depressed, conical, having- an open um- 

 bilicus, crenulated at the internal margin of the vs'ind- 

 ings of the spire, at its base ; the opening nearly quadran- 

 gular (see T. perspectives, pi. 7. /. 94). 



MoNODONTA. Shell oval or conoid ; the aperture entire and 

 roundish, with the two margins disunited at the upper 

 part, the projecting and truncated or shortened base of 

 the pillar forming a tooth projecting into the opening 

 (see T. Labio, jd. 7. /. 95). 



Fhasianella *. Shell solid, ovate, or conical ; the aperture 

 longitudinal, ovate, and entire, with a sharp plain lip ; the 

 pillar smooth, witli an attenuated base (see pi. l.f. 96). 



Pyramidella. Shell tapering ; the aperture entire and semi- 

 oval ; the pillar projecting, with three transverse folds, 

 and perforated at its end (see T. dolabratus, pi. l.f. 97). 



* See Park. Organ. Rem. vol. 3. p. 83. 



R 2 



