XVIU 



" Gtrotoma. — Shell turreted ; columella incurved, above 

 callously thickened ; aperture oval, subetfuse at the base ; lip 

 simple, acute, narrowly profoundl}^ fissured above. 



" Animal. — Operculum corneous, spiral." 



This forms one of the most distmet of the. genera 

 of Strejjomatidce. Mr. Lea, however, anticipated 

 Mr. SlmttleAVorth's discovery. 



Dr. Brot, in his admirable " Systematic Catalogue 

 of the Melanians," proposes, instead of the genera of 

 H. & A. Adams, a series of sections, which are gen- 

 erally excellent, for the arrangement of the species. 

 The following is his plan : — 



1. Operculum concentric. 



Genus Paludomus, Swainson. 



2. Operculum spiral or subsjnral. 



* Aperture entire. 



Genus Leptoxis, Raf. 



{Anculotus, Say ; Anculosa, Conr.) 



Genus Melania, Lam. 



Group a, type canaliculata, ^^y- 

 curvilabris, Anth. 

 Haysiana, Lea. 

 a, type Virginica, Say. 

 costidata. Lea. 

 pierangulata, Conr. 

 simplex. Say. 

 Warderiana, Lea. 

 nupera, Say. 

 (European.) 

 keoissima, Sowb. 

 glcq}Jiyra, Morelet. 

 nigritinn, Morelet. 

 (All the other groups of this section, thirteen in number, are 

 exotic.) 



** Aperture produced in front. 

 Genus lo, Lea. 

 *** Aperture truncate in front. 



(Melanopsis, Hemisinus.) 

 **** Aperture posteriorly sinuate. 



Genus Gyrotoma, Shuttlw. 

 ***"** Aperture sinuate in front and posteriorly. 

 (PiRENA, Lam.) 



