with a revision of the ZimnceidcB of Authors. 343 



Shell patelliform, apex dextral, margin simple. 



Ancylus {paraUelus, jhiviatUis). 



Buccal plate horseshoe shaped (in all the species?); (equivalent 

 to the three plates of IAmncea, fused) smooth or papillose. 



Tentacles short, blunt, cylindrical, dilated at the bases, widely 

 separated. Eyes sessile on the inner bases. 



Genitalia on the left side. Foot short, bluntly rounded behind. 



Mantle margin simjde. 



Central tooth simple ; inner laterals strongly bidentate ; outer 

 ones notched, much as in Limncea. 



Ova as in Acroloxus. 



Shell patelliform, apex sinistral, margin simple. 



These animals are monoecious, but cannot reciprocally im- 

 pregnate one another at the same time. 

 They copulate only in pairs. 



Gundlachia (califomica, Jfeekiana). 



Buccal plate ? 



" The soft parts agree so closely with the true Ancyli that I have 

 not succeeded in finding any differences of importance — except the 

 form of the visceral sac." Stimpson. 



Genitalia on the left side ? 



Cusp of the central tooth bifid. Laterals with three or more 

 oblique denticles. 



Shell ancyliform, apex inclined to the right. In the adult shell a 

 lamina closes two-thirds of the apex from the rest of the shell. In the 

 cavity thus formed, some of the viscera are enclosed. Margin simple. 

 Ova? 



Latia {a ncylifo rm is) . 



Dr. Gray gives the following description, which he says is 

 imperfect, being taken from a dried 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 the outer edge of their base. (?) Body 



