i 



38 



CONTRIBUTION TO THE PALEONTOLOGY OF TRINIDAD. 



percrassa or 0. compressirostra; but it has become completely hidden by a most 

 singular denosit of silicon in concentric rings. Apparently, the two valves 



silicon in concentric rings. Apparently, the two valves 



rest together with a layer of the silicious rock matrix between. The surface 

 of the convex valve has been completely encrusted by the concentric rings of 

 silicon, so as to be perfectly hemispherical; while the flat valve is completely 

 hidden in four layers of similar but finer concentric rings of the same character. 

 The singular appearance of this most curious specimen is heightened by the 

 brilliant coloring of the silicious circles which vary from deep violet, moss green, 



and white to vivid pink. 



This coloration is shown to be due to some organisms probably marine algae 

 that were living on the surface of the rings. For when heated in the flame of a 

 bunsen burner the pink color turns black and then fades out, a sure proof that 



it is organic. 



It is needless to say that identification of the oyster shell forming the nucleus 



of this mineral growth is impossible. But attention is called to the structure, 



as it is so very unique and characteristic. The beginnings of the formation of 



the concentric rings have been seen on other fossils in this bed, as on Ostrea cyn- 



thice, but in this case it has been carried to an extreme development. 



Locality. — Bed No. 2, Soldado Rock, Gulf of Paria. 



Geological horizon, — Midway Eocene. 



Ostrea pulaskensis Harris. Plate VII, Figure 2. 



Gryphaa vomer Safford, Geol. of Tennessee, p. 419, 1869. 

 Gryphaa pitcheri Morton? White, Proc. U. S. Nat. Mus., vol 

 Ostrea pulaskensis Harris, Ark. Geol. Surv., vol. II, p. 40, pi. 

 Gryphaa vomer Langdon, Geol. Surv. Alabama, p. 416, 1894. 



Dall, Trans. Wagn 



160-161 



1896 



Harris' original descript 



Outline of the larger valve right angle-trian 



gular ; a carination from the umbo to the posterior basal margin forming the 

 hypothenuse, the basal margin the base, and the shorter margin from umbo to 

 base the perpendicular with proportional lengths of 8,7 and 5 respectively; beak 

 generally very incurving; carination often very pronounced; between it and 

 the margin of the valve are one or two more or less distinct sulci ; surface com- 

 paratively smooth, though possessing a few slight concentric undulations, which, 

 curving upwards in the middle of the valve, form a very shallow sulcus extending 

 from beak to base; muscular impression not distinctly marked; lesser valve 

 thin, flat, circular; marked exteriorly by lines of growth, smooth within, with 

 an oval muscular impression which is submarginally located. 



"This description, and the figures referred to, show the most Gryphsea-like 



phase of this species 



Other forms are less distinctly sulcate and carinate 



it 



Georg 



Midway Eocene of Texas, Arkansas, Tennessee, Mississippi, Alabama, and 



Remarks 



A specimen of this curious little oyster from Soldado Rock 



