CONTRIBUTION TO THE PALEONTOLOGY OF TRINIDAD. 37 



Ostrea cynthiae new species. Plate VI, Figure 5. 



Description. — Shell large, heavy, becoming greatly thickened, general form 

 obliquely ovate-oblong; left (lower) valve very convex, not plicated, marked by 

 thick, irregular concentric lamellae marking resting periods of growth; right 

 (upper) valve flat, operculate in form, not sculptured ; hinge not heavy, considering 

 the weight of the shell. 



Height 140, greatest breadth 90 mm. 



Remarks. — These oyster shells have been almost wholly replaced by silica, 

 only a few narrow layers of the original calcite remaining deep in the inner 

 portion of the shell. The silicious deposits form on the surface very curious 

 concentric structures, one of which is shown in the figure near the base of the 

 valve. 



This oyster is unlike any described from the lower Eocene of either North 

 America or Brazil. 



It is with great pleasure that the writer names the species in honor of Mrs. 

 Arthur Sewall, of Philadelphia. 



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



Geological horizon. — Midway Eocene. Equivalent to the Midway of Ala- 

 bama and that of the Rio Maria Farinha beds, State of Pernambuco, Brazil. 



Ostrea golfotristensis new species. Plate VII, Figure 1. 



Description. — Valves rather thin, when complete, ovate-oblong in form; 

 sculpture of very many fine, close-set, radiating riblets, divaricating, fairly 

 regular; hinge with a narrow, rather deep ligament pit. 



Height of fragment 15 mm. 



Remarks. — Superficially this curious shell resembles somewhat a Midway 



Alabama fossil mentioned by Professor Harris as PlicaUda species, 8 but the 



Soldado shell has no teeth, — only the deep ligament pit showing it to be an 

 Ostrea. 



It appears to be of the group of Lea's Ostrea divaricata; 9 but the divaricating 

 riblets are very much finer and more close-set than in that species. The form 

 of the shell is also much less oblique. 



The specimens are all more or less broken. The curious aspect of this shell 

 is enhanced by the fact that it is colored moss-green, magenta, and violet by 

 presumably some marine algal growth that has encrusted it. The peculiar 

 formation of concentric rings of silicon on the surface has begun in some cases. 

 This is noted at greater length in the description of the other Ostreas from Soldado. 



Locality.— Bed No. 8, Soldado Rock, Gulf of Paria. 



Geological horizon. — Lignitic Eocene. 



Ostrea cf. percrassa Conrad and compressirostra Say. Plate VI, Figure 7. 



Among the Ostreas from Bed No. 2, Soldado Rock, is a very bizarre specimen. 

 It was evidently originally a large rounded oyster of the general shape of 0. 



Bull. Am. Pal 



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ons to Geology 



