133 



Genus 3. ELENCHUS, Humphrey. 



Animal ; ? 



Shell ; conical, pyramidal, but not flattened at the base, whorls 

 convex, margins disjoined. Substance of the shell a stout 

 horny periostracum, lifted with a thin bright iridescent nacre. 



The term Elenchus has been applied for some years past to a group of 

 shells somewhat limited in number, but very deserving of generic honour. 

 Though uniform in shape, the species are perhaps most distinguished for 

 the peculiarity of their composition, being little calcareous and richly 

 iridescent. The typical character of the genus may be recognised in the 

 well-known Trochus iris, so remarkable for the brilliant iridescence of its 

 pearly nacre ; the species here selected for illustration is another equally 

 distinguished in this respect, and there are several interesting small species, 

 composing Mr. Gray's genus Thalotia, from New Holland. 



For list of species of tins and other imperfectly named genera, which the 

 author proposes to work out in the Conchologia Iconica, see Appendix. 



Figure. 



Elenchus circulatus. PL 12. Pig. 57. Shell, showing its pyramidally 



ovate form and iridescent interior. — From Mr. Cuming's collection. 



Genus 4. BAN KI VI A, Deshayes. 



Animal; ? 



Shell ; elongated, subulate, with the surface polished, somewhat 



porcellanous, columella thickened, rolled over, twisted, truncated 



at the base ; aperture rather small, lip thin. 



Such is the generic description of a shell of winch there are several 

 differently coloured varieties, but only one species, which has been mixed 

 up along with the Troclins iris in the genus Elenchus. It appears to have 

 been first distinguished by M. Deshayes in PL 70. Fig. 8, of his 'Traite 

 Elementaire de Conchyliologie ' and, as I learn, was intended as the type 



