AND ALLIED FORMS. 45 



B. abhreviata, Moq.-Tand., loc. cit. II, (1855), 519, pi. xxxviii, fig. 37, 38. 

 — Paludina ahbreviata, Mich. Western Europe. 



B. conoidm, Moq.-Tand., loc. cit., II, (1855) 522, pi. xxxix, fig. 3-5.— 

 Pahtdina conoidea, Reys. Western Europe. 



B. brevis, Moq.-Tand., loc. cit., II, (1855) 523, pi. xxxix, fig. 6-10.— C^- 

 clostotna breve, Drap. Western Europe. 



B. siviilis, Moq.-Taxd., loc. cit., II, (1855) 526, pi. xxxix, fig. 18, 19. — Cy- 

 clostoma simile, Drap. Western Europe. 



B. Nickliniana, St^i.— Paludina Nicliiniana, Lea, Tr. Am. Phil. Soc, VI, 

 (1839) 92, pi. xxiii, fig. 109. Pennsylvania. 



B. Binneyi, Stm. — Pomatiopsis Binneiji, Tryon, Proc. Acad. Nat. Sci. 

 Pliilad., 1863, p. 148, pi. i, fig. 10. California. 



See also on p. 20, ante, for others. 



This genus differs from Amnicola in its lingual dentition, the 

 rhachidian tooth having but one basal denticle. It differs from 

 Littorinella in having a bifid verge -,, and from Faludestrina in the 

 shape and obtuse apex of the shell, and in the want of perceptible 

 denticulation on the cusp of the outer lateral tooth of the lingual 

 ribbon. 



Moquin-Tandon's varicose BythinellfB, B. marginata and B. 

 gibba, are not included in the above list of species, because they 

 present characters in the shell which may indicate important dif- 

 ferences in the soft parts. Whether they are true Bythinellae 

 remains to be determined by future examination. 



If the type of Hartmann's genus Eydrobia should prove to be 

 a fresh-water species, that name will have to be adopted in place 

 of Bythinella for this genus. 



The name Leachia, of Risso, must be rejected on account of its 

 previous use by Lesueur for a genus of Cephalopoda. Lesueur's 

 name is considered synonymous with Loligopsis by Gray,^ but the 

 group seems to be sufficiently distinct from the typical Loligop- 

 sides in the tuberculation of the body. 



For further remarks upon the genus Bythinella, see ante, p. It. 



PALIJDESTRIl^A, D'Orb. 

 Paludestrina, D'Orbigny, in Sagra's Cuba, Moll., II, (1841) 8. 



Shell conic, more or less elongated, smooth, imperforate or 

 nearly so ; apex acute. Aperture ovate ; peritreme continuous ; 

 outer lip acute ; inner lip not thickened. Operculum corneous. 



' Cat. Moll. Brit. Mus., Ceph. Antep., p. 39. 



