1. albella, Loven. 



2. carinata, Adams. 



3. crassior, Montagu. 



4. fragilis, Menke. 



172 



Species. 



5. labiosa, Loven. 



6. neritoidea, Gould. 



7. pallidula, Da Costa. 



8. puteolus, Turton. 



9. uuifasciata, Carpenter. 

 10. vincta, Montagu. 



Figure. 



Lacuna pallidula. PL 17. Fig. 89. Shell, of the subglobose form of 

 the genus, showing the characteristic umbilical groove. 



Family 12. MELANIANA. 



Shell ; turriculated or globose, covered ivith an olive or black epi- 

 dermis, variously sculptured. Aperture sometimes entire, some- 

 times notched at the base. Animal flwoiatile, furnished with a 

 horny epidermis. 



Univalve river mollusks, affecting rapid streams in contiguity with the 

 sea, are numerous in species, but all may be included under this family 

 in three genera. Their shells are for the most part of solid structure, 

 covered with an olive or black horny epidermis, differing essentially in this 

 respect from those of the family Lymnceana, which inhabit more stagnant 

 water ; and they have frequent indications of rough usage in being more 

 or less eroded or decollated. 



Genus 1. MELANOPSIS, Ferussac. 



Animal ; similar to that of Melania. 



Shell ; fusiform or conically cylindrical, generally covered with a 

 black homy epidermis; apex sharp, but often decorticated; 

 columella smooth, often callous at the upper part, and more or 

 less truncated at the lower ; aperture rather small, sometimes 

 notched above, conspicuously notched below; lip scarcely re- 

 flected. Operculum horny, spiral, small. 



The shells collected under the head of Melanqpsis are distinguished from 

 the Melania proper by much the same character as Achatina among land 

 shells is distinguished from Bu limns, namely, in being notched at the base, 



