No. 109.] 



87 





RhTUCHONELLA. PLEIOrLEUEA. 



"VValdheimia globosa. 



Pal. N.Y. Vol.iii, pi- 36, f. 1. 



Shpll subglobose, oval : ventral valve a little larger than the 

 opposite one, most gibbous in the umbonial region ; beak promi- 

 nent, rounded an.l arched, perforate at the extremity by a round 

 aperture, one side of which is formed by a deltidium ; dorsal 



