No. 109.] 89 



Waldheimia rectirostea. 



Pal. N.Y. Vol. iii, pi. 36 a. " 



Shell longitudinally ovate, tapering towards the beak at an angle 

 of about 45*^, slopes on each side of the beaks, flattened and not 

 plicated ; beak of ventral valve straight, extending beyond the 

 opposite, truncated at the apex by a round perforation partly 

 formed by the del-tidium ; beak of dorsal valve incurved. Sur- 

 face marked by twelve or thirteen prominent subangular plica- 

 tions, the two central of which, on the ventral valve, are slightly 

 smaller than the others, and a little depressed. These two plica- 

 tions coalesce before reaching the beak : the central plication of 

 the dorsal valve is smaller and a little more depressed than the 

 others, and becomes obsolete before reaching the beak. 



This well-marked species may be at once distiDguished from either of 

 the preceding by its less ventricose form, and the more attenuated and 

 straight beak of the ventral valve. 



Geological position and locality. Oriskany sandstone, Maryland. 



Waldheimia deweyl 



Pal. N.Y. Vol. iii, pi. 36, f. 3. 



Shell depressed-subglobose, sometimes subquadrilateral with the 

 sides curving, moderately compressed ; valves nearly equal : 

 ventral valve a little the most prominent towards the umbo, 

 having a narrow faint sinus from near the beak to the front, 

 where it sometimes produces a slight sinuosity ; beak apparently 

 not perforate, extending a little beyond the opposite beak, upon 

 which it is closely incurved : dorsal valve symmetrically arched. 

 Surface marked by about forty regular simple rounded striae, 

 crossed by indistinct lines of growth, and, near the front, oc- 

 casionally by stronger imbricating concentric marks indicating 

 interrupted stages of growth. 



Geological position and locality. Shaly limestone of the Lower Helder- 

 berg group, Albany county. 



