CHAP. HI. THE NASSIN^E. 6$ 



from this, it does not appear to have a probosciform 

 mouth; but the anterior part of the foot is prolonged into 

 a subulate point on each side, and the hinder part termi- 

 nates in two little 

 tail-like appendages. 

 Now this has much 

 of the character of 

 our genus Leiodo- 

 mus *, figured by 

 Quoy and Gaimard; 

 and, although both 

 they and their shells are too dissimilar to be placed 

 in the same group, they may be considered analogous. 



(60.) The broad, spreading, and dilated inner lip of 

 Cassis prepares us at once for the sub-family of NASSIN-B, 

 which is entered by the genus Cassidaria of Lamarck. 

 These shells differ from all those we have just left, by 

 having the basal canal considerably more lengthened, 

 and only slightly turned backwards, without reposing on 

 the shell itself: they are of an intermediate size be- 

 tween the largest Nassce and the smaller helmets ; and 

 thus the gradation even of size is preserved. The typi- 

 cal genus Nassa then succeeds : the species, although 

 all of them small, are much varied in shape, and in the 

 degree in which the inner lip is developed; but the 

 twisted ridge at the base of the pillar, the striated aper- 

 ture, and the tuberculated tooth at the top of the aper- 

 ture, are so constant, that they must remain as they now 

 are in our systems, until their sub-genera are worked 

 out. There is one form, however, so very remarkable, 

 that we have placed- it as the genus Cyclonassa * : it is 

 the only snail-shaped flattened shell in this tribe ; and 

 the animal, when known, will no doubt be very curious. 

 Our next genus, Vexilla, opens the passage to the 

 Purpurina, which it perfectly resembles in general 

 form, and in its broad depressed inner lip ; but the outer 



* Bucc. agathe Quoy, Voy. Astral, pi. 31. fig. 17. 



f Cyclops of Montford ; but this is a long established genus of crabs. 



