INVERTEBRATE PALEONTOLOGY. 15 



Osin'ii pellucida, M. & H. 



Plate 28, figs 4, a, 6. 



Ostrea larva, Hall and Meek (1854), Mem. Adii. Acad. Sci. and Arts, Boston, V, (n.s.), 406. — M. & H. 



(Nov., 1856), Proceed: Acad. Nat. Sci. Philad., 286 (not 0. larva, Lam.) 

 Ostrea jirlliicida, Meek and Hayden (Oct., 1860), Proceed. Acad. Nat. Sci. Philad., 429. 



Shell small, thin subovate or elongate-oval, arcuate laterally, usually 

 attached from the umbo to near the middle of the under valve; borders 

 undulated, so as to form a few. obscure plications, which extend but slightly 

 in from the edge; margins near the cardinal end distinctly crenate; surface 

 with moderately distinct marks of growth, which sometimes become nearly 

 obsolete. Lower valve convex, usually with a well-defined scar of attach- 

 ment ; upper valve nearly flat, or more or less convex near the beak. 



Length, from beak to the opposite extremity, 1.32 inches; breadth, 0.70 

 inch ; convexity, 0.40 inch. 



This species resembles somewhat O. larva of Lam. (— O. falcata, 

 Morton, Synop. Org. Rem., p. 50, pi. 3, fig. 5, and pi. 9, figs. 6-7), and is the 

 same shell referred with doubt to that species in the papers above cited. A 

 careful comparison of other specimens shows that it is clearly distinct, as it 

 is never near so strongly and regularly plicated as O. larva, and is always 

 entirely destitute of any traces of auricular appendages, and wants the 

 straight hinge of that species ; while it has a large and distinct scar ot 

 attachment, showing that the under valve was attached from the beak to near 

 the middle. In the latter character, it is more like O. crenulata of Tuomey ; 

 but it wants the closely-set squamose ridges of that species. 



From the last-described species, it differs in having its margins waved 

 or subplicated, and in not being attached by the whole of its under surface. 

 In the few obscure flexures of its lateral margins, it approaches the Alectry- 

 onia group ; but as it wants the straightened hinge and auriculate character 

 of that group, and has the plications but slightly developed, it may about as 

 well go with the typical oysters. 



Locality and position. — Long Lake and Moreau River; from the Fox 

 Hills group, or No. 5 of the Cretaceous series of the West. 



Ostrea (Gryphxostrea!) subalata. Meek. 

 Plate 28, fig. 5. 



Shell small, longitudinally oval, more or less arcuate laterally; margins 

 waved, or forming some four or five obscure undulations, which extend but 



