80 



POPULAR CONCHOLOGY. 



them on the Continent. The substance of shells seems to 

 be formed of three plates, the central generally being the 

 thickest, and the outer one the thinnest. The Italian 

 cameo cutters are aware of this circumstance, and cle- 

 verly avail themselves of it in cutting the cameos, the 

 ground being always formed of the innermost layer of the 

 three, which is also generally the most transparent.* Mr. 

 Woodwards observes, that the cameos in the British 

 Museum carved on the shell of C. cornuta are white on 

 an orange ground ; on C. tuberosa and Madagascariensis, 

 white on a dark claret colour ; on C. rufa, pale salmon 

 colour on orange ; and on Strombus gigas yellow on pink.f 



Morio. Montf. (Cassidaria Lam.) — Shell rather ob- 

 long ; spire not much elevated ; mouth 

 long, and rather narrow, terminating in 

 a canal, which is recurved, but does not 

 touch the back; left lip often rough or 

 wrinkled, and detached from the pillar; 

 right lip thickened ; exterior of shell trans- 

 versely grooved, and often spotted with 

 round tubercles ; operculum horny. Ani- 

 mal nearly like that of the Cassis. — 5 

 species ; also fossil. 



These shells chiefly come from the seas of warm lati- 

 tudes ; one or two species are found in European countries. 



Oniscia. Sow. — Shell oblong, rather ob- 

 tuse; spire short, base rather pointed: mouth 

 longitudinal ; canal very short ; outer lip thick- 

 ened, toothed within ; inner lip expanded and 

 covered with raised spots : outside ribbed. 

 Animal not known. — 6 species: also fossil. 



Morio cchmophora. 



' Gray; Philosophical Trans. 



t Keevo's Iconica. 



