232 Bulletin 39 404 



subcircnlar shell of the Upper Chesapeake is the typical form. 

 The Costa Rican shells are most like the Upper Chesapeake 

 typical acetabulum . 



Brown and Pilsbry have described a smaller and more finely 

 sculptured species from the Gatun Spillwa}^ as delicatissima. 

 This spceies is represented in our collection from the same place 

 and appears to be distinct. Toula's specimen from Gatun, how- 

 ever, is a true acetabuluvi. 



The Dosinia acetabulum is a common fossil in the Gatun 

 beds of Costa Rica, where it occurs most abundantly in the 

 lower part of the formation. 



Gatun Stage: Gatun, C. Z. 



Hotel and Hone Cree k. 

 Pu77ibri Creek. 

 Hill No. J, Ba7iana River, 

 Coll. 6, Estrella River. 



Genus CLEIVIENTIA, Gray 

 dementia dariena Conrad Plate 31, figure 4 



Meretrix dariena Conrad, 1856, Pacific R. R. Reports, vol. 5, p. 328, 



pi. 6, fig. 55. 

 dementia dariena Gabb, 1881, Journ. Nat. Sci. Phila. , vol. 8, p, 344, 



pi. 44. fig. 16. 

 dementia dariena Dall, 1903, Trans. Wagner Free Inst. Sci., vol. 3, 



pt. 6, p. 1235. 



detnentia dariena Toula, 1908, Jahrb. der K-K. Geol. Reichsanstalt, 



vol. 58, p. 725, pi. 27, figs. 9, 10. 

 dementia dariena Hubbard, 1920, Scientific Survej- of P. R. and the 



Virgin Islands, vol. 3, pt. 2, p. 118, pi. 19, figs 10-12. 



This species is very common in the lower Gatun of the 

 Canal Zone. It is very rare in western Panama and in Costa 

 Rica, where it occurs in the lower part of the Gatun formation 

 and in the Uscari shales. Romanes* has recorded it from Bar- 



* Quart. Journ. Geol. Soc. London, 1912, vol. 68, p. 125. 



