224 



SHELLS AND SHELL-FISH. 



that of Senectus to Ampullaria; both being large globose 

 shells, and the latter sometimes closed with a shelly 

 operculum. The curious reader, who may be desirous 

 of prosecuting these analogies further, may compare 

 them, at his leisure, with many others in the volume. 



(209.) We shall now bring together the genera of 

 the two sub-families. 



Analogies of the Senectin^ and the Trochin^. 



Genera of the 

 Senectin^, 



Senectus. 



Marmarostoma. 



Delphinula. 



Cyclocantha ? 



CiDARIS. 



Analogical Characters. 



("Typical of their respective circles; 7 

 I volutions convex. 3 



f Sub-typical ; umbilicus with a ba- 7 

 I sal groove. S 



f Nearly discoid; umbilicus very 7 

 i deep ; pillar none. " 5 



Shell not perlaceous ; trochiform. 

 r Aperture oblique ; operculum 7 

 I shelly. i 



Genera of the 

 TrochinjE. 



Trochus. 



monodonta. 



scalaria. 

 Onustus. 

 Canthorbis. 



Our only doubt relates to what is the true type 

 between Delphinula and Cidaris. It is either the shells 

 we have before mentioned, or those of which Turbo 

 pagodus is the type, where the opercidum is horny. 

 We may now turn to the 



Analogies of the Sub-genera 0/ Canthorbis. 



Sub-genera of 

 Canthorbis. 



Tubicanthus. 



Canthorbis. 

 Pyramidea. 

 Lamprostoma. 

 Carlnidea. 



Analogical Characters. 



f Aperture obliquely round or oval; 7 

 \ smooth. 3 



f Greatly depressed ; the sides ca- 7 

 i rinated ; umbilicus small. y 



Aperture thin, sharp, brittle. 

 ("Aperture strongly toothed ortu-7 

 I berculated ; striated within. 5 

 ("Aperture nearly entire, slightly 7 

 \ angulated ; smooth within. j 



Genera of the 



TROCHINiE. 



Canthorbis. 



Onustus. 

 Solarium. 



MoNODONTA. 



Trochus. 



The results of this table will explain why we have 

 thought it expedient to characterise as sub-genera the 

 types of such a small group as Canthorbis ; for the shells 

 it contains are so remarkably varied, that, without some 



