108 CONTRIBUTION TO THE PALEONTOLOGY OF TRINIDAD. 



"This seems to be an extremely variable species, both as to general shape 

 and as to the form of the mouth. It is distinguished from the preceding (E. 

 ly coper sicus Guppy) by its small circular vent and wider ambulacra. The mouth 

 is usually subpent agonal, but occasionally becomes transversely oval. Some 

 examples which approach the circular form have a tendency to become subcorneal. 



"San Fernando, Trinidad." 



Remarks. — Among the Echinoderms from Farallon Rock was one exactly 

 like Dr. Guppy's figure 46. 



Locality. — Farallon Rock, near San Fernando, Gulf of Paria. 



Geological horizon. — Lower Oligocene. Equivalent to the San Fernando beds 

 of which this horizon appears to be a continuation. 



EXPLANATION OF PLATES V-XIII. 



PLATE V. 

 Fia. 1. Ostrea abrupta d'Orb. var.? Valve showing plicated exterior. Venezuela. Cre- 



Page 



taceous. Height 25 mm 40 



2. Ostrea abrupta d'Orb. var.? Interior of a larger valve. Venezuela. Cretaceous. 



Height 45 mm 40 



3. Ostrea puelchana d'Orb. Small variety. Height 47 mm. Union Estate, Brighton, 



Trinidad. Oligocene 40 



4. Ostrea puelchana d'Orb. Same shell as 3. Interior of flat valve 40 



5. Ostrea puelchana d'Orb. Same shell. Interior of convex valve 40 



6. Ostrea thirsce Gabb. Convex valve. Height 28 mm. Soldado Rock. Lignitic Eocene 39 



7. Ostrea thirsce Gabb. Same shell, lateral view 39 



8. Ostrea thirsce Gabb. Flat valve. Height 20 mm. Soldado Rock. Lignitic Eocene . . 39 



9. Ostrea puelchana d'Orb. Large variety. Height 135 mm. Union Estate, Brighton, 



Trinidad. Oligocene 40 



10. Ostrea puelchana d'Orb. Same shell, lateral view m ** 



11. Ostrea crenulimarginata Gabb. Smooth and plicated valves. Soldado Rock. Midway 



Eocene 36 



PLATE VI. 



P»ge 



Fig. 1. Ostrea crenulimarginata Gabb. Exterior of left valve. (After Aldrich and Harris.) 



Alabama • * \ 



2. Ostrea crenulimarginata Gabb. Interior of left valve. (After Aldrich and Harris.) 



Alabama • m 



3. Ostrea crenulimarginata Gabb. Interior of unusually rounded form. (After Aldrich and 



Harris.) Alabama • • • • 6 



4. Ostrea crenulimarginata Gabb. Young shell, rounded variety. Height 25 mm. Soldado 



Rock. Midway Eocene d 



5. Ostrea cynthice n. sp. Flat, upper valve resting on convex lower. Height 140 mm. 



Showing commencement of concentric deposits of silicon. Soldado Rock. Midway 

 Eocene ^L 



6. Ostrea thalassoklusta n. sp. Height 23 mm. Soldado Rock. Midway Eocene. . ••%••• 



7. Ostrea cf. percrassa Conrad and compressirostra Conrad. Shell completely disguised 



by concentric silicious deposits. Length 130, height 90 mm. Soldado Rock. Midway 

 Eocene 6i 



PLATE VII. 



Page 



Fia. 1. Ostrea golfotristensis n. sp. Height of fragment 15 mm. Soldado Rock. Lignitic 



Eocene • • 61 



2. Ostrea pulaskensis Harris. Height 22 mm. Lateral view showing lines of growth. 



Soldado Rock. Midway Eocene ?i 



3. Plicatula cf . torta Gabb. Rio Grande, Venezuela. Cretaceous 



