159 Midway Stage 45 



PART II. PAI/BONTOI/OGY. 



Description of the Molluscan Remains of the Midway 



Stage. 



Pelecypoda. 



OSTREA. 



rPl. I, fig. I, a, 

 Ostrea crenulimarsrinata, \ PL 2, fig. i, a, 



(Pl. 3, fig- I- 



Syn. O. crenuliniarginata Gabb, Jr. Phila. Ac. Nat. Sci., 2d 

 ser., vol. 4, i860, p. 398, pi. 68, figs. 40, 41. 

 O. denticulifera Gabb, non Con., Ibid., p. 398. 

 O. denticulifera Safford, non Con., Geol. of Tenn., 1869, 



p. 419. 

 O. prcB-compressirostra Harris, Ark. Geol. Surv., vol. 2, 



1892, publ. in June, 1894, p. 39. 

 O. compressirostra I^angdon, non Say., Geol. Surv. Ala., 



1894, p. 413- ^ ., . 



O. tumidtda Aldrich, Geol. Surv. Ala., Aug., 1894, P- 



242, pi. 14, figs. I & 2, pi. XV, figs. I & 2. 



Gabb's original ^^^m)!'/?^?^.— " Subtriangular, sometimes elon- 

 gated, oval; attached; portion of the outside of the shell not 

 attached is very squamose; hinge about an equilateral triangle, 

 central groove of the hinge deep; internal margin strongly crenate, 

 muscular impression large; upper valve?. 



''Dimensions. — I^ength 2.2 in., greatest width about 2 in. 



"Z^m/zVj/.— Found in a marl bank, two miles east of Middleton, 

 Tenn. Rather common and associated with O. denticufera Con." 



The type specimens of this species were very kindly lent me by 

 Dr. Safford. The figured specimen, fig. 40, op cit., was attached 

 during growth to a nearly flat fragment of wood and hence does 

 not show well the radiating plications, yet they are indicated in 

 one place. One of the specimens grew on a Vetiericardia plani- 

 costa, and shows ribbing. Gabb for some unknown reason select- 

 ed out the most of the left valves in Safford' s collection and named 

 them crenulimarginata, while the right valves he styles denticu- 

 lifera; all these I have before me. They are small and immature. 

 The characters of the species are well shown on pi. i, fig. i, a, 

 and pi. 2, fig. I, a, after Aldrich. The lesser valves when joung 

 present a peculiar pyri-circular outline and are smooth, thin and 

 convex. Such specimens are common i mile north of Midway. 



