66 



SHELLS AND SHELL-FISH. 



PART I. 



the whole circle of the Testacea. It will be needless in 

 this place to enter into the definitions of this and the 

 other four genera, since they will be found in our sys- 

 tematic arrangement; but they may shortly be cha- 

 racterised in the following manner : In Cassidea and 

 Dolium, the aperture of the shell is always wide, rarely 

 with distinct varices, and the outer lip never dilated into 

 a marginal rim over the body- whorl; but in the first, the 

 inner lip is reflected, thickly marginated, and generally 

 toothed, while in the last it is always thin : these will 

 be found, upon analysis, to be the two typical genera. 

 In the harps (Harpa), which obviously follow the tuns 

 (Dolium}, the whole shell is marked by varices, which 

 assume the form of ribs. Now, the ample information 

 given by M. Quoy on the animal of this genus, not 

 only fixes its station in the present circle, but demon- 

 strates it to be a representation of the volutes, with 

 which that admirable malacologist compares it. This im- 

 portant point being determined upon such high authority 

 and unpremeditated testimony, we arrive, by induction, 

 at the station of the two remaining types. CyprcR- 

 cassis, consequently, intervenes between Harpa and 

 Cassis; and this latter fills up the interval between Cy- 

 prcecassis and Cassidea. Thus, the Cassin<E, like the 

 Muricina, form a circle of affinity among themselves, 

 and present one of the most beautiful set of analogies 

 to be found among the families of Testacea. 



Analogies of the GASSING to theFamilies of GASTEROPODA. 



Genera of the 

 CASSINJB. 



CASSIDEA. 

 DOLIUM. 



HARPA. 



CYPRJBCASSIS. 



CASSIS. 



Analogies. 

 basal channel 



never 7 



CTypical ; 

 I straight. 



Sub-typical. 



Foot of the animal enormously 

 large ; mantle dilated ; tenta- 

 cula short. 



Aperture of the shell linear ; both"] 

 lips regularly toothed, the in- j 

 ner spreading, but never pro- 

 minent ; aperture with a chan- | 

 nel at each extremity. J 



Outer lip gibbous or angulated} 



above, considerably dilated on f 



its margin ; eyes of the animal I 



C highly developed. ) 



Families of 

 GASTEROPODA. 



MURICID*. 



TURBINELLID.fi. 



VOLUTID.E. 



STROMBIDJE. 



