343 
wiih a revision of thè Limnceidce of Authors. 
Shell patelliform, apex dextral, margin simjile. 
Ancylus {^'parcdlelus, Jluviatilis). 
Buccal piate horseshoe shaped (in all thè species?); (equivalent 
to thè three plates of Limncea, fused) smooth or papillose. 
Tentacles short, blunt, cylindiical, dilated at thè bases, widely 
separated. Eyes sessile on thè inner bases. 
Genitalia on thè left side. Foot short, bluntly rounded behind. 
Mantle margin simple. 
Central tooth simple ; iimer laterals strongly hidentate ; outer 
ones notched, much as in Limncea. 
Ova as in Acroloxus. 
Shell patelliform, apex sinistrai, margin simple. 
These animals are monoecious, bxit cannot reciprocally im- 
pregnate one anotlier at thè same time. ’ 
Thev copulate only in pairs. 
Gundlachia {calìfornica, 3Ieekiand). 
Buccal piate ? 
“ The Soft })arts agree so closely -with thè trae Ancyli that I bave 
not succeeded in finding any diiferences of importance — except thè 
form of thè visceral sac.” Stimpson. 
Genitalia on thè left side ? 
Cusp of thè centrai tooth bifid. I^aterals with three or more 
oblique denticles. 
Shell ancyhform, apex inclined to thè right. In thè adult shell a 
lamina closes two-thirds of thè apex from thè rest of thè shell. In thè 
cavity thus formed, some of thè viscera are enclosed. Margin simple. 
Ova ? 
Latici {ancyliformis). 
Dr. Gray gives thè following description, which he says is 
imperfect, being taken from a clried specimen which had been 
soaked in weak potash and water : 
Head with a short broad snout, rounded in front. Tentacula short, 
triangular. The eyes on thè outer edge of their base. (?) Body 
