FROM PLIOCENE CLAY BEDS IN COSTA RICA. 373 



Diameter about half an inch. 



This little shell is common in the clay beds, but, unlike most of the other 

 fossils, the inclosed matrix is very hard, and so firmly cements the two valves 

 together that even by destroying one or several shells, I have been unable to make 

 out all of the details of the hinge. What I have seen seems most like that of 

 meretrix, but the reference is rendered somewhat doubtful by the absence of a 

 lunule. The shell can be recognized by its small size, its compressed sides and its 

 subquadrate, or rather subpentagonal form. 



PSEPHIS, Cpr. 



P. CANCELLATA, n. s., PI. 47, fig. 74. 



Shell small, subtrigonal, compact ; beaks acute and prominent, base regularly 

 rounded; surface marked by fine concentric ribs, crossed by others of an equal 

 size radiating from the beaks ; lunule long and slender ; inner margin entire. Of 

 about the same size and shape as the West Coast P. tantilla, Gld. ; this species can 

 be at once distinguished by its minute cross sculpture. P. tantilla is marked only 

 by a few concentric lines. 



CARYATIS, Roem. 



C. L'ORDLYI, n. s. 



Shell trigonal, gibbous ; beaks anterior ; anterior end narrowly produced, most 

 prominent a little above the middle; posterior end prominent, base regularly 

 rounded. Surface marked by fine concentric striae, most distinct on the anterior 

 end ; lunule broad, bounded by a fine, elevated, thread-like line. Internal margin 

 entire. 



Length, one inch. 



Nearest to C. albida, but differs in being more cuneate posteriorly and in the 

 sculpture. Named after Dr. C. R Lordly, formerly of Limon, now of Cartago, 

 Costa Rica, who materially aided me in making this collection. 



C. GuppYANA, Gabb, n s., PI. 47, fig. 73. 



Shell moderate in size, thin, convex, short, and almost subtriangular when 

 young, growing more oval as it increases in size. Beaks prominent; anterior end 

 broadly rounded, curving with an unbroken curve across the lunule to the beaks. 

 Posterior end broad and round ; base regularly convex. Surface polished and 

 ornamented by numerous small, regular, concentric ribs. Lunule large, and 

 bordered by a sharply impressed line. 



Figure. Natural size ; drawn from the largest specimen, which is unfortunately 

 broken. Four others of smaller size confirm the above diagnosis. 



