LAMELLIBEANCHIATA OP THE LOWER MAELS. 33 



Owing to the great variability among the individuals of species it is nearly 

 or quite impossible to identify with certainty the internal casts, especially 

 where they are taken from collections that have been made by others under 

 circumstances where no note has been taken or pi'eserved of the markings 

 on the matrix. It is therefore with great doubt that I have assigned to anj- 

 given species the casts which I have examined. 



Formation and locality. — From the green clays under the second marl 

 of the Lower Green Sand at the pits of W. Lippincott, esq., Shrewsburj-, 

 N. J. In the collection of the Academy of Natural Science, Philadelphia, 

 there is a specimen bearing this name, which is evidently a specimen of 0. 

 conipressirostra, and has the locality marked in ink on the specimen as 

 Chickasaw Bluffs, which I believe is considered as Eocene. 



Ostrea tecticosta. 



Plate III, Figs. 1 and 2. 



Ostrea tecticosta Gabb. J. A. N. Sci., Phil., new ser., Vol. IV, p. 403, PI. LXVIII, Figs. 

 47 aud 48. Syuopsis, p. 154. Meek, Check-list, p. 6. Geol. Siirv. K J., 1868, 

 p. 724. 



Shell small, elongate, oval, ovate or irregularly elliptical in outline, 

 slightly curved, with a small, strongly-twisted beak and moderately-sized 

 ligamental area on the lower valve. The lower valve usually shows a large 

 cicatrized area of attachment and is strongly plicated, the plica being usuall}' 

 sharply rounded and very rugose from concentric lamellose lining. The 

 inner margins of the valves are also crenulated on the upper half or two-thirds 

 of their length, and more minutely so on the inner border at the junction 

 of the valves just below the ligamental area. Muscular scar large, but only 

 moderately marked. Upper valves slightly convex and destitute of plica- 

 tions except near the border. 



I have only seen a single lower valve of this species from the Creta- 

 ceous beds of New^ Jersey, where it would seem to be a rather uncommon 

 species, though quite abundant in Tennessee. All the shells have an 

 extremely immature look, as if they were the young of a larger shell, but 

 as none such have been observed corresponding in characters, we must 



admit it as a species for the present. The New Jersey specimen presents 

 4418 MON 9 3 



