1866.] GXJPPY WEST-INDIAN TERTIARIES. 583 



I do not know of any recent or fossil West-Indian species at all 

 resembling this shell, which seems to be related to E. ohliqua, 

 Caillat {E. nitidula, Desh.), of the Paris basin. 



Lower Miocene, Manzanilla, Trinidad. 



14. Arca Trinitaria, spec. nov. 



Shell solid, snbtriangular, oblique, rather inequilateral, with about 

 forty unarmed ribs, which occasionally become imbricated towards 

 the ventral margin ; umbones prominent, curved, separated by a 

 ligamental area with grooves corresponding to the anterior hinge- 

 teeth ; posterior margin nearly flat, cordate, divided from the disk 

 by an abrupt angular carination; anterior edge short, rounded; 

 ventral edge nearly straight; inner margin strongly dentate. 

 Hinge-teeth numerous, lamellar, the lateral ones bent into an angle. 



Allied to A. ponderosa, Say. It may easily be distinguished by 

 the number of ribs and by other characters. It may possibly have 

 been confounded with A. incongrua by the Geological Survey ; but it 

 is very distinct from that species. A. Trinitaria may be distinguished 

 from all other Arks with which I am acquainted by the strong angu- 

 lar posterior ridge and flat posterior margin, which give so peculiar 

 an appearance to the shell. The lateral hinge-teeth, which are bent 

 into the form of an L, also afford a good character for the distinction 

 of this species. 



Lower Miocene, Manzanilla, Trinidad. 



15. Arca filicata, spec. nov. 



Shell subquadrate, oblique, somewhat inequilateral, rather inequi- 

 valve, with about thirty ribs, broader than their interstices, and 

 nodosely crenate, becoming nearly smooth on the disk of the right 

 valve ; beaks prominent, oblique, their apices rather remotely sepa- 

 rated by a broad and well- developed lanceolate ligamental area; 

 margins strongly dentate, rounded, forming angles anteriorly and 

 posteriorly with the hinge-line, which is straight, and furnished with 

 a regular series of small parallel teeth. 



A species allied to A. pexata, but having the umbones separated 

 by a well-developed ligamental area, which is nearly wanting in 

 that shell. 



Lower Miocene, Manzanilla, Trinidad. 



16. Grtph^a athyroides, spec. nov. 



Shell oval, gibbous, slightly irregular; upper valve convex, 

 marked by deep and wide sulci of growth; lower valve broadly 

 carinate along its mesial portion from the umbo to the front mar- 

 gin, plicated by several obsolete radiating folds ; lines of growth 

 strongly marked, undulated ; umbo small, produced, and abruptly 

 truncate. 



This oyster resembles an irregular Brachiopod ; and the umbo of 

 the lower valve is produced and truncated by a circular concavity 

 resembling a foramen, but which does not extend into the interior. 

 The microscopic structure also excludes it from the class Brachiopoda. 



San Fernaiido beds, Trinidad. 

 VOL. xxTi. — part I. 2 b. 



