CONTRIBUTION TO THE PALEONTOLOGY OF TRINIDAD. 53 



During the Midway stage, but especially during the Lignitic of the southern 

 United States, V. planicosta showed a vast number of variations. 29 But at the 

 close of the Eocene the species absolutely disappeared. No representation is 

 found in the Oligocene, Miocene or Pliocene of North America. Curiously 

 enough, however, the recent analogue of V. planicosta occurs only on the Pacific 

 coast in warm waters. 



Locality. — Bed No. 2, Soldado Rock, near the Serpents Mouth, Gulf of Paria. 



Geological horizon. — Midway Eocene. Equivalent to the Midway beds of 

 Alabama and of Rio Maria Farinha. State of Pernambuco, Brazil. 



Venericardia thalassoplekta new species. Plate VIII, Figure 17. 



Description. — Shell of moderate size, subcordate, convex; posterior end of 

 valve concealed in a silicious matrix; anterior and central portion of left valve 

 beautifully sculptured with (a) narrow, elevated ribs, which, beyond the anterior 

 third of the valve, become nodular, (6) two less elevated, intercalary, smooth, 

 rounded riblets, equalling one another in size but narrower than the ribs them- 

 selves. 



Height 22 mm. 



Remarks.— A single specimen of this fine shell was found. It is closely 



allied to V. alticostata; but differs in having the two interstitial riblets and in the 

 ribs being quite smooth over the anterior part of the valve. 



The specific name has been given because the sea by constantly striking on 

 the reef has fortunately eroded it in such a way as to leave the fossils standing 

 more or less in relief. 



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

 Geological horizon. — Midway Eocene. 



Genus CARDITA (Bruguiere 



Cardita (Carditamera) Virginias 



Figu 



Description. — Shell rather small, elongate-elliptical, very inequilateral, beaks 

 low, situated at the anterior fourth of the entire length of the valve; sculpture 

 of fifteen or sixteen well defined ribs, which on the short anterior end of the shell 

 are regularly and closely crenulated, but on the long, posterior part of the shell 

 are smooth or nearly so; characters of the hinge concealed by the matrix. 



Length of shell 13, height 7 mm. 



Remarks.— This species is most closely allied to Dr. Dall's Carditamera 

 tegea from the Oligocene of the Tampa silex beds and the Chipola marls of Florida. 



It may, indeed, if more specimens are found, grade into a varietal form of 

 that shell. 



The presence of a species of Cardita and especially of one near of kin to a 

 Chipola species strengthens the evidence already offered by other species that 

 the horizon in which it was found is Upper Oligocene. 



" See Harris, Bull. Amer. Pal., II, pp. 246-247. 1897. 



