343 



Costa Rica Miocene — Olsson 



ORDER PRIONODKSMACEA 



. Genus HUCULk Lamarck 



Wucula orisiceHa, n. sp. Plate 28, figures 19, 20 



Shell of medium size, broadly elliptical or subovate in out- 

 lines; obliquely truncated at its anterior end; gently convex; the 

 surface is covered with close, subregular, concentric wrinkles and 

 fine radial threads so that the sculpture is decussated; on the 

 posterior dorsal slope, they are larger and pustular-like and their 

 course is obliquely downward across the growth -lines; they are 

 weak on the poorly defined lunule; the radical threads are main- 

 ly between the concentric wrinkles but ventrally they cut into 

 the wrinkles as well; interior of the shell, silvery white or faint- 

 ly tinged with purple; the ventral margin is finely crenulated; 

 chondrophore very small, oblique; anterior set containtng about S 

 teeth, the posterior with about 17. 



Length 9.50, height 7.50, semi-diameter 2.25 mm. 

 11.00 8.50 2.50 mm. 



From the recent A^. crenulata A. Adams, this shell differs 

 by its larger size and more elliptical and deprCvSsed shell. Gabb 

 has described from the Pliocene of the Limon Peninsula Nu~ 

 cula limofiensis and moe7ie?ists, but both of these species are per- 

 fectly smooth and sculptureless. The Nucula orbicella is a com- 

 mon species in certain marly beds intercalated in the coralline 

 limestones of Port Limon. 



Gatu7i Stage: Port Limon, 



NlDCUla cahuitensis, n. sp. Plate 18, figures 21-24 



Shell small, solid, obliquely subtrigonal in form; ventral 

 margin widely rounded, a nearly straight posterior dorsal margin 



