35 ^ Costa Rica Miocene — Olsson 179 



Glycymeris jamaicensis Dall, 1898, Trans. Wagner Free Inst., Sci., 



vol, 3, pt. 4, p. 608. 

 Glycymeris jamaicensis Maury, 1917, Bull. Amer. Pal., vol. 5, p. 345, 



pi. 26, fig. 13. 



This large Pectunculid, externally resembles in its angular 

 posterior side the Glycymeris pennacea with which it was confus- 

 ed by Guppy and by Gabb, It differs in being somewhat less con- 

 vex, less strongly sculptured and most importantly in its central 

 beaks, located about the middle of the ligamental area. It is, on 

 the other hand, much more closely allied with the recent West 

 Indian G. undatus Linne (6^. lineatus Reeves) of which it is 

 doubteless the Miocene ancestral form, the main difference being 

 in details of its finer sculpture. 



The Glycymeris jamaicefisis occurs in the Miocene of Jamaica 

 and Santo Domingo but there never seems to reach the large size 

 that the species sometimes attains in Costa Rican. A large shell 

 in our collection from Old Man Sam Creek measures as fol- 

 lows: 



Height 60, lenght 60, diameter of both valves 37 mm. 



Gatun Stage: Water Cay. 



Coll. 5, Red Cliff Creek. 

 Coll. ^a^ East Grape Poiiit Creek. 

 Colls. 5, 6, Old Man Sa77i Creek. 

 Sousi Creek of Upper Hone Creek. 



Glycymeris carbasina Brown and Pilsbry Plate 19, figures I, 2, 5 



Glycymeris carbasina Brown and Pilsbry, 191 1, Proc. Acad. Nat. Sci. 

 Phila., vol. 63, p. 363, pi. 28, fig. 9. 



The Glycymeris carbasina was described by Brown and Pils- 

 bry from a small individual from Gatun, measuring only 16 mm 

 in height. It is closely related to the G. jajnaicensis Dall and 

 probably represents but a varietal form. Its main differences is 

 its more circular and less convex shell, and less number of hinge- 

 teeth which number about 10 to 12 on the anterior and posterior 

 sides respectively. 



