419 



Costa Rica Miocene— Olsson 



247 



Chione holocyma Brown and Pilsbry Plate 30, figure 9 



Chione ulocyma Dall, variety holocyma Brown and Pilsbry, 191 1, Proc. 

 Acad. Nat. Sci. Phila., vol. 63, p. 369. 



Associated with mactropsis, in the Central Zone is a more 

 convex and finely sculptured shell, allied to the ulocyma Dall of 

 of the Floridian Miocene. It is the holocyma of Brown and Pils- 

 bry. We have seen no typical ulocyma from Panama. 



From mactropsis, the holocyma will be distinguished by its 

 generally smaller, more convex and more circular shell. Its 

 concentric lamellae are more numerous and less confluent and 

 with fine but persistent radial stride. It is generally best distin- 

 guished by its smaller and less clearly differentated foliaceous 

 area on its anterior extremity, which in mactropsis is as wide 

 an area as that along its posterior dorsal margin. 

 Heigth 29, length 36.5, thickness 19 mm. 



Galun Stage: Ml. Hope, C. Z. 



Chione hotelensis, n. sp. Plate 32, figure 7 



Shell small, subtrigonal, heavy, but slightly convex; sculp- 

 ture of about 15, thick, rounded and evenly spaced concentric 

 lamellae; on the posterior-dorsal slope, the ends of the lamellae 

 become attenuated, thin and somewhat appressed as in glyptocy- 

 7na Dall of the Flordian Miocene; the lamellae themselves are 

 smooth and rounded but with their interspaces finely radially in- 

 cised by small lines; escutcheon rather large, smooth; lunule 

 small, cordate and smooth except for the growth lines, 

 Length 23, height 19, thickness 12.5 mm. 



This elegant little species is distantly related to the C. gly- 

 ptocyma Dall from the Oak Grove sands of Florida, but is a 

 smaller and more compact shell. The radial striations commence 

 on the ventral surface of the lamellae and are continued across 

 the interspace to the base of the next rib. 



All of our specimens were collected in a hard sandstone in 

 the lower Gatun of Hotel Creek near Old Harbor, Costa Rica. 



