NATURAL SCIENCES OF PHILADELPHIA. 567 



Descriptions of some New Species of Tertiary Fossils from Chiriqui, Central 



America. 



BY W. M. GABB. 



The following species were collected by Dr. John Evans during his examina- 

 tions, under the patronage of the U. S. Government, in Chiriqui. I have, as 

 yet, received no definite information in regard to their exact locality or geo- 

 logical position. The material is too scant to form a definite idea in regard to 

 their age, but I believe them to be Miocene. Full information on the subject 

 will be contained in Dr. Evans's report. It is worthy of notice that among a 

 large number of specimens there should be so few species. The matrix is a 

 dark, almost black, highly bituminous shale. 



Terebra. 



T. E v a n s i i . Shell turrited, whorls about eight or nine, angulated above; 

 suture distinct; surface polished and marked by an impressed line about a 

 third of the width of the whorl from the upper edge ; below marked by several 

 faint revolving lines. Aperture subquadrate, columella somewhat prolonged, 

 tortuous, and with two faint folds ; outer lip sinuous, most prominent near the 

 lower part of the mouth. Rather common. 



Dimensions. Length, 1 inch ; width of body-whorl, -5 in. ; length of aper- 

 ture, -4 in. 



Tellina. 



T. semilaevis. Shell subtriangular, truncate posteriorly, inequilateral ; 

 beaks one-third of the distance from the posterior extremity, with a faint 

 angulation extending from them, parallel with the posterior side, to the 

 margin ; posterior side nearly straight ; posterior angle obtuse ; anterior end 

 regularly rounded ; surface, in the young state, smooth ; in the adults, with the 

 marginal half concentrically striate. Very rare. 



Dimensions. Length, -6 in.; width, -75 in.; thickness, -35 in. 



Chione. 



C. sulcata. Shell ventricose, robust, produced posteriorly; umbones 

 large and round ; anterior margin regularly rounded, basal sinuous, posterior 

 nearly straight. Umbonal ridge rounded, with the shell posterior to it at a 

 right angle with the rest of the shell, and with a very distinct depression or 

 sulcus anterior to it. Surface marked by about twenty heavy transverse ribs, 

 crossed by numerous radiating impressed lines. Inner margin crenulate 

 Rare. 



Dimensions. Length, '6 in.; width, -8 in.; thickness, -6 in. 



Arca. 



A. Chiriquiensis. Ventricose, inequilateral, umbones very large ; 

 hinge line short, with the teeth very small and at right angles to the hinge. 

 Surface marked by numerous radiating ribs, with the depressions between 

 them of about the same size as the ribs : these are crossed by very distinct 

 lines of growth ; and on the ribs are numerous small nodes, which appear to 

 be independent of the lines of growth, and are not merely squamose elevations. 

 These nodes are most prominent on the anterior ribs, and become gradually 

 fainter posteriorly until, posterior to the umbonal ridge, they disappear. Area 

 wide and marked by very few angular lines. This species is exceedingly 

 common, and is sometimes nearly three inches across. 



Dimensions of the most perfect specimen. Length, 1*5 in.; width, 1-6 in. ; depth 

 of valve, -8 in. 



Membranipora. 



M. speciosa Gabb and Horn. Colony in small encrusting patches, com- 



I860.] 



