431 Costa Rica Miocene — Oi^son 259 



variety costaricensis in the lower part of the Gatun formation. 

 Gatun Stage: Sousi creek. 



Semele Clayton! Maury Plate 29, figure 2 



Semele Claytoni, Maury, 1917, Bull. Amer. Pal., vol. 5, p. 227, pi. 35, 

 fig. 9- 



The 5*. Claytoni was described by Dr. Maury from the Cer- 

 cado formation, Santo Domingo of Lower Miocene age. It is a 

 large species, reaching a length of 66 mm or more and charact- 

 eristically sculptured with even, concentric lamellae like the re- 

 lated species from the Tertiaries of eastern United States as chipo- 

 lana Dall, Leana Dall and perlaniellosa Heilprin. From these, 

 the 5". Claytoni is distinguished in having its radial striae nearly 

 obsolete. Our specimen from Costa Rica is fragmentary but 

 probably measured when perfect 38 by 30 mm. 



Uscari Stage: Hotel creek. 



Genus ABRA, (Leach) Lamarck 

 Abra triangulata Dall Plate 29, figure 10 



Abra triangulata Dall, 1900, Trans. Wagner Free Inst. , Sci., vol. 3, 

 Pt. 5, p. 997, pl- 49. fig- 4. 



A small, rotund or trigonal species abundant in the shale 

 beds of Bocas Island. The valves are nearly equilateral, the an- 

 terior end slightly the larger and inflated. vSurface smooth and 

 shining. The type was described by Dall from the Bowden beds 

 of Jamaica. Our specimens are a little larger, measuring: 



Length 7.25, height 6.50, diameter of the left valve 

 1.75 mm. 



Gatun Stage: Bocas del Toro. 



