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36 CONTRIBUTION TO THE PALEONTOLOGY OF TRINIDAD. 



DESCRIPTIONS OF SPECIES. 



Class PELECYPODA. 



Genus OSTREA Linnaeus, 1758. 



Ostrea crenuHmarginata Gabb. Plate V, Figure 11; Plate VI, Figures 1, 2, 3, 4. 



Ostrea crenuHmarginata Gabb, Jour. Acad. Nat. Sci. Phila., 2d ser., vol. IV, p. 398, pi. 68, figs. 40, 



41, 1860. 

 Ostrea denticulifera Gabb, Ibid., p. 398. Not of Conrad. 

 Ostrea prce-compressirostra Harris, Ark. Geol. Surv., vol. II, p. 39, 1894. 

 Ostrea compressirostra Langdon, Geol. Surv. Alabama, p. 413, 1894. Not of Say. 

 Ostrea tumidula Aldrieh, Geol. Surv. Alabama, p. 242, pi. 14, figs, 1, 2, pi. XV, figs. 1, 2, 1894. 

 Ostrea crenuHmarginata Harris, Bull. Am. Pal., vol. I, pp. 159-160, pi. I, figs. 1, la, pi. II, figs. 1, 



la, pi. Ill, fig. 1, 1896. 

 Ostrea crenuHmarginata Dall, Trans. Wagner Inst. Sci., vol. Ill, p. 677, 1898. 



GaWs original description. — " Subtriangular, sometimes elongated, oval, at- 

 tached; 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. — Length 2.2 in., greatest width about 2 in." 



Type locality near Middleton, Tennessee, in Midway Eocene marls. 



Remarks. — Gabb was misled by the great dissimilarity in appearance of the 

 convex, plicated left (or lower) valves and the nearly flat, smooth right (or upper) 

 valves of this species; and gave to the former the name crenuHmarginata and 

 to the latter denticulifera, supposing them to be two species. 



Among the oysters from Soldado Rock, Bed No. 2, are a number of almost 

 flat valves, of elongated oval, or elliptical outline, and sculptured only by rather 

 coarse concentric lines of growth. These, so far as one can judge from the ex- 

 terior, agree well in form with the flat valves of specimens of 0. crenuHmarginata 

 from the Midway of Alabama. 



A young Ostrea shell was found in Bed No. 2, which shows the characteristic 

 crenules on the inner margin. It is much like specimens of a varietal form 

 found near Midway, Alabama,which are flat and nearly circular in outline. 

 This shell shows on the exterior faint radial striae. 



We have also from Bed No. 6, Soldado Rock, a single convex valve embedded 

 in a silicious matrix with a mass of Foraminifera. The hinge area and a portion 

 of the exterior is, however, revealed. The former shows along the margin fine 

 striations, like specimens of crenuHmarginata but somewhat closer and finer; 

 and the surface of the shell shows traces of the rather regular, narrow plications 

 characteristic of the left valves of this species. As the general outline also 

 agrees, the writer is inclined to think that the shell from Bed No. 6 is a left 

 valve of 0. crenuHmarginata. 



Locality.— Beds Nos. 2 and 6, Soldado Rock, Gulf of Paria. 



Geological horizon. — Midway Eocene (Bed No. 2) and near the Midway and 

 Lignitic contact zone (Bed No. 6). 



Jl NV 



