108 UNIVALVES. TROCHUS, 



TROCHUS.— Top-Shell. 



Animal — a Limax: Shell univalve^ spiral^ more or less 

 conic: aperture somewhat angular or rounded; the up- 

 j)er side transverse and contracted; pillar placed ob^ 

 liqueli/» 



The genus Trochus contains .one hundred and thirty- 

 three species. Among so large a number, considerable 

 differences may naturally be expected ; however, the lead- 

 ing characteristic, which in the Trochi consists in the 

 shape, is more or less retained throughout the major part 

 of the species. Yet, in many instances, some of them are 

 so very nearly allied to the following genus, turbo, that 

 frequent mistakes arise in their classification. 



The form of the Trochi is invariably conical, though 

 some arc much more obtuse than others; all, however, 

 have a broad base, the whorls gradually tapering upwards 

 to the apex or tip, thereby assuming the shape of a py- 

 ramid. 



Among those Trochi which have their pillar perforated 

 or umbilicated, may be mentioned the Trochus Niloticus, 

 Trochus maculutus, Trochus perspectivus (stair-case), 

 Trochus Hybridus, and Pharaonis, &c. &c. 



Though some of this genus have their surfaces almcwt 

 smooth, yet a far greater number may be found that are 

 covered with knobs, spines, tuberculations, or undulations. 

 The Tiochus Solaris or golden sun, and the Trochus ini- 

 perialis or imperial sun, from the South seas, may per- 

 haps be sufficient examples. The former has its margin 

 beset with long spines, placed at regular distances, and 

 which, when the shell is perfect, resemble very nearly 



