XXIU 



natural genus, and adopted it in his descriptions. 

 In Philos. Trans., vm, p. 163, he proposed to sepa- 

 rate the species of Melania according to certain 

 obvious, external (by no means generic) characters, 

 for facility in their determination. He described a 

 large number of species under the following divis- 

 ions : — 



"1. Smooth. 4. Sulcate. 7. Granulate. 



2. Plicate. 5. Striate. 8. Caneellate. 



3. Cariuate. 6. Tuberculate. 9. Spinose." 



Perhaps this division of the species suggested to 

 Messrs. Adams the genera which they have adopted 

 in their classification. 



In Philos. Trans., iv, p. 122, Mr. Lea proposed to 

 institute a new genus, lo, for the Fusus Jlumalis of 

 Say. His description is, "lo. — Shell fusiform; base 

 canaliculate ; spire elevated ; columella smooth and 

 concave." 



In his description of Melania excisa, and Ancfido%a 

 incisa, published in Philos. Proc, ii, p. 242, Dec, 

 1842, Mr. Lea suggested the name Schizostoma for 

 those species having a pleurotomose sutural slit in 

 the outer lip. The genus thus proposed, and which 

 bears the same relation to Gotiiobasis as Schazicheila 

 does to Helicina, was sometime afterwards charac- 

 terized by Mr. Shuttleworth, from independent ob- 

 servation, under the name of Gyrotoma. 



In Philos. Proc, Aug., 1845, and in the Transac- 

 tions, X, p. 67, 1853, Mr. Lea j^ublished the following 

 description of his genus : — 



" ScnizosTOMA, Lea. Shell conical or fusiform. Lip fis- 

 sured above. Aperture ovate, columella smooth, incurved. 

 Operculum. — 



"xso operculum has come under my notice; but I can 

 scarcely doubt that it will be found to be horny, and to resem- 

 ble, in other respects, that of Melania." 



Subsequently (vol. x, p. 295), Mr. Lea says, 

 "When I ])roposed the name of Schizostoina for a 

 genus of Melaiiiana with a cut at the superior por- 



