3tt2 On thè genus Pomphólyx and its Allies, 
Tentacles long, filiform ; eyes on a tubercular expansion of thè inner 
bases. 
Genitalia on thè left side. Foot very short, blnntly rounded. 
ISIantle margin simple, not extending beyond thè shed. 
Cusp of centrai tooth bidentate. 
Laterals broad ; inner tridentate, outer with more or less nume- 
rous notches. 
Ova capsules rounded, in a delicate envelope. 
Shell depressed, spirai or discoidal ; dextral. 
Gray figures thè lateral jaws of P. corneus. I have obtained them 
from P. lentus / yet, as far as I know, they have not been noticed in 
thè smaller species, although they probably exist, but of extreme deli- 
cacy, and cartilaginous consistency. 
Cam^ytoceras ( terehra). 
Buccal piate ? 
Tentacles filiform, blunt. Eyes large, situated between thè ten- 
tacles. 
Genitalia on thè left side? Foot shorter than thè aperture. 
hlantle margin simple, not extending beyond thè shed. The an- 
terior part of tlie head moderately produced. 
Teeth ? Ova ? 
Shed sinistrai, turreted, loosely coiled. 
The oiily inforniation tvhich we have of this singular forni is 
thè deseription of Mr. Benson, who places it near Ancylus. 
Acroloxus (lacustris). 
Buccal piate strongly arched, papillose. Two lateral accessory 
plates, not continuous as in Ancylus. 
Tentacles distant, stout, cylindrical, pointed ; bases expanded ; eyes 
near thè inner sides. 
Genitalia on thè right side. F oot rounded behind. 
Mantle margin simple. 
Teeth ? 
Ova capsules discoidal, covered witli a minutely tuberculose tough 
envelope. 
