26 RESEARCHES UPON THE HYDROBIIN.E 



acute, and about equal in size ; the cusp is armed with five den- 

 ticles, and the broad central one has apparently an additional 

 very minute one at its base on either side. Tlic intermediate 

 tooth has a moderately broad peduncle, and its cusp is armed with 

 six denticles, of which the third from within is much larger ilian 

 the others. The lateral teeth are shaped generally as in the allied 

 genera already described ; the cusp of the inner one has ten den- 

 ticles, and that of the outer one six or seven. The outer lateral 

 tooth when reversed or thrown outward, is seen to have a some- 

 what expanded truncated extremity upon wliich all the denticles 

 are placed — none appearing on the sides. 



It will be observed that this dentition is very distinct from that 

 of Lepioxis or any other Melanian genus, the latter never having 

 basal denticles on the rhachidian tooth. 



Attached to the shell of some of the specimens before me, I 



find a thin brownish capsule (Fig. 17), about one-eigbth of an 



inch in diameter, containing egirs, which is in 

 Fi" 17 ' o ».- ' 



°' ' all probability the ova-capsule of the Flumini- 



cola. It is disciform, very little convex, and 

 /^) ,-^ attached by its broadest surface which forms 



1^ the circular base. It contains about twenty- 



four ova, and is thus very distinct in character 

 from the ova-capsules of the other genera of 

 Hydrobiina;, for in all other cases as yet observed, the eggs are 

 deposited singly. The ova-capsules and their various modes of 

 deposition, undoubtedly afibrd good generic characters. 



The genus Fluminicola seems to be restricted to the fresh- 

 waters of the countries bordering on the Pacific coast of North 

 America, all the species yet known being from California and 

 Oregon. The genus will include, besides the type, F. Nuttalliana, 

 the following sjiecies : — Paludina virens, Lea ; P. nuclea, Lea ; 

 F. seminalis, Hinds ; and Amnicola Hindsii, Baird. 



Geuus OILtlA, Stm. 

 Fig. 18. Ill September, 1863, while on a visit at the resi- 



dence of my friend Mr, Binney, at Burlington, X. J., 

 I enjo3a^d oi>portanitie3 of studying the soft parts of 

 Ilelama altilis^ of Lea (Fig. 18), which indicate a 

 generic type diflferent from any yet described. 



' Placed in Leptoxis by Haldemau, Moiiog. Lept., 6, pi. v, fig. 152. 



