MANUAL OF THE MOLLUSCA. 



[Family Eissoid^] 



Includes LiTlOPA (p. 255), Eissoina (p. 256), EissoA (p. 255)^ 

 and the following additional genera : — 



DlA-STOMA, Deshayes, 1864. 



Type, Melania costellata, Lamarck. 



Shell elongated, turreted ; wliorls with varices ; aperture very- 

 oblique, semi-lunate, entire; base sinuated, subangular; pos- 

 terior angle acute, detached from tlio penultimate whorl; lip 

 thin, curved ; columella concave, depressed, narrow. 



Fossil, 4 species. Eocene. Paris basin. 



Amphithalamtjs, p. Carpenter, I860. 



Type, A. inclusus. West Coast of North America. 



iShell like Bissoa, nucleus large ; aperture with a produced 

 lip, suddenly contracted in the adult. 



This genus bears the same relation to Bissoa that Stoastoma 

 does to Helicina. 



Keilostoma, Deshayes, 1848. 



Type, Melania marginata, Lamk. 



Shell elongated, turriculated, regularly conical; generally 

 striated transversely. Aperture entire, short, effuse at the base, 

 angulated posteriorly ; columella short, callous ; the peri- 

 stome entire, the left lip broad and thick, the right broadly 

 margined. 



Fossil, Eocene, 6 species ; Paris basin. Belgium, England, 

 J^unjaub. Cretaceous, 5 species ; India, Gosau. 



Pterostoma, Deshayes, 1864. 



Type, P. tuba. Eocene. Grignon, Paris. 



Shell elongated, turriculated ; peristome continuous, circular, 

 very dilated and margined ; columella very broad, expanded, 

 and continuous with the peristome. 



ScALiOLA, Adams, 1860. 

 Type, S. bella. 



Animal with the rostrum elongated, cylindrical, annulated, 

 bifid at the end ; tentacles filiform, eyes Trominent, black at 

 the outer base of the tentacles ; foot short, ovate, posteriorly 

 sub-acuminate; operculum corneous, ovate, subspiral; nucleus 

 eubterminal. 

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