102 I Senate 



bous above than below the centre ; beak prominent, slightly 

 arched ; extremity perforate ; perforation generally connected 

 with the broad triangular foramen below, but probably often 

 separated by the deltidial pieces, which, with the thickened 

 dental apophysis, nearly or quite close the foramen : dorsal 

 valve depressed-convex, slightly the smaller ; beak scarcely in- 

 curved. Surface apparently smooth, or marked only by obscure 

 concentric lines and faint wrinkles of growth. 



The specimens examined are silicified, and it is probable that fine 

 radiating striae may have existed on the original shell, which have been 

 obliterated by the change. 



This species may be distinguished from M. suessana, which it most re- 

 sembles, by its more elongate form and the more prominent beak of the 

 ventral valve. The cardinal margin of the ventral valve, on each side of 

 the beaks, is also more prominent, and that of the other valve mo<re ex- 

 cavated, so as to impart a waved outline to the line of junction of the two 

 valves from the bealis along the lateral slopes. 



Geological position and locality. Orislcany sandstone, Maryland. 



Megantbris OVOIDES. 



Pal. N.Y. Vol. iii, pi. 104 & 105, f. 1. 



Terebratula oroides, Eaton (1832) : Geol. Text-book. p. 45. ( Not Sowerby, 



1812.) 

 T perovalis, Eaton (1832) : Geol. Text-book, p. 45. (Not Sowerby, 1825.) 

 Atnjpa elongata, Conkad : An. Rep. N.Y. 1839, p. 65. 



Not Meganieris elongatu ( Pentamerus elojigatus ) of the Onondaga limestone, 



Vanuxem: Geol. Rep. 1842, p. 132, f.l. 



Shell elongate-ovate or elliptical-ovate, gibbous or compressed, 

 broadest above the middle, abruptly rounded towards the car- 

 dinal end, narrowing to the front, which is often depressed and 

 roun !ed or subtruncate ; no traces of a sinus in either valve : 

 in gibbous specimens, the sides are sometimes vertically flattened 

 or a little concave, often slightly contracted near the front : 

 ventral valve the larger, most gibbous in the umbonial region ; 

 beak (in old specimens) somewhat obtuse, closely incuiVed 

 upon the opposite : dorsal valve depressed-convex, less elevatet^. 

 than the other, most prominent along the middle or a little 



