133 



Genus 3. ELENCHUS, Humphrey. 



Animal ; ? 



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

 convex, margins disjoi7ied. Substance of the shell a stout 

 horny periostracum, lined loith 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 honoui'. 

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

 the peculiarity of their composition, being little calcareous and riclily 

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

 well-known TrocJms iris, so remarkable for the brilhaut iridescence of its 

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

 distinguished in this respect, and there are several%teresting small species, 

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



For list of species of this and other imperfectly named genera, wliich the 

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



Figure. 



Elenchus circulatus. PI. 12. Fig. 57. Shell, showing its pyramidally 

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



Genus 4. BANKIVIA, Deshayes. 



Animal; ? 



Shell ; elongated, subulate, loith the surface polished, someivhat 



porcellanous, columella thickened, rolled over, twisted, truncated 



at the base ; aperture rather small, lip thin. 



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

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

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

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

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



