I lO 



BULI.ETIN 39 



Uscaid formation. Coco Plu7n, Panama, 

 Rio Codes. 

 Comadre Creek, etc. 



Genus PERfSTERiViSA Morch 



Peristeriiia insula, n. sp. Plate 8, figure ii 



Shell small, with a sharp pointed spire, a little longer than 

 the aperture; the general form and sculpture of the shell is like 

 that of Urosalpin.x cinereus Say; nucleus of 2 small smooth 

 whorls, followed by 7 post-nuclear; the profile of the spire- whorls 

 is convex and strongly sculptured with ribs and sharp spiral cords; 

 the last whorl has 8 ribs which are nearly lacking from the base 

 of the whorl; the spiral sculpture consists of 2 principal cords 

 about the middle of the earlier whorls above which lie smaller 

 threads about the suture; on the later whorls, the spirals are 

 somewhat heavier about the middle but irregular with finer, in- 

 termediate threads in between the principal ones; base contract- 

 ed; aperture subcircular; outer and inner lips crenulated or den- 

 ticulated; canal short and bent. 



Height 23, diameter 13, aperture 11 mm. 



This and the following tortugera seem correctly referable to 

 the genus Peristernia Morch. The P. i?isula is somewhat like 

 young specimens of Jilicata Conrad, from the Chesapeake Mio- 

 cene of eastern United States, but has a longer and more pointed 

 spire, and heavier sculpture. 



Gatun Stage: Water Cay. 



Peristernia tortugera, n. sp. Plate 8, figure 13 



Shell elevated with a spire much longer than the aperture; 

 nucleus of about 2>^ small, smooth whorls; the post-nuclear 

 whorls about 7; sutures distinct; whorls strongly convex, should- 

 ered; sculpture of narrow, heavy ribs, widely spaced and num- 

 bering on the last whorl about 9; the rib are continued across the 

 whorls from suture to suture and for a short distance down on 



