LAMELLIBEANCHIATA OF THE LOWER MAELS. 71 



described species. The extremely ventricose form of the body of the valve 

 and angular umbonal ridge at once distinguishes it from any knov\'n form. 

 Formation and locality. — In the dark micaceous clays below the Lower 

 Marls at Haddonfield, N. J. From the collection of the Academy of Nat- 

 ural Sciences, Philadelj)hia. 



MELEAGEmELLA, u. gen. 



Shell aviculoid having the general form of Meleageina Lam. 

 (■=Margaritophora Megerl.) but differing principally in the form of the byssal 

 fold of the right valve, which is either a deep channel on the external 

 surface of the shell extending from the margin to near the beak of the valve 

 or a simple deep straight notch separating the wing into a linear process, of 

 greater or less length, from the body of the shell. Shells biconvex; hinge 

 straight; ligamental area narrow, but distinct, strongest on the left valve, 

 which is also the most convex, and more or less gaping opposite the notch 

 of the right valve. A single muscular scar of large size occurs subcentralh' 

 behind the middle of the valves; other muscular scars unknown. Surface 

 lamellose or lamellose-radiate, with a fine radiate iibrous glistening texture 

 like that of Placumomya. Types M. curta {zziAvicula curta Hall) and M. 

 orhiculata^iPseudomonotis {Enmicrotis) orbicidafa Whitf Black Hills Rept., 

 p. 356, PI. HI, Figs. 17-19. 



This genus is more nearly related to Meleagrina Lamarck than to any 

 other described form. In the Palaeont. of the Black Hills I referred the two 

 typical species to Enmicrotis, Meek, which he considered as a division of 

 Pseudomonotis, Brown, following Mr. Meek's own reference in so doing, with 

 the remark that it might take the name Eumicrotis, providing the Permo- 

 carboniferous forms on which that genus was founded, should be found not 

 to conform too nearly to Brown's genus Pseudomonotis, but as I suppose this 

 would not be admissible, I have thought it more proper to propose a new 

 genus for it. Dr. F. Stoliczka, in his discussions of the Avicididce. in vol. iii, 

 Pal. Indica, considers Eumicrotis and Pseudomonotis as synonymous ; but 

 certainly our American Permo-Carboniferous forms referred to Enmicrotis 

 are very distinct from the forms referred originally to Brown's genus. 



