429 Costa Rica Miocene — Olsson 257 



hinge is completely concealed in all our specimens. It has the 

 form of the M. Conradi Dall, from the Chesapeake Miocene of 

 United States but is higher and differs in many other respects. 

 It is shorter and higher than M. gatunensis Toula with which it 

 may occur. 



Gatun Stage; Hill No. j, Banana River. 

 Rio Betey. 



Subgenus PSAIVilVlACOIVlA, Dall 



Macoma gatunensis Toula Plate 26, j5gure 13 



Macoma ( Tellina) gatunensis Toula, 1908, Jahrb. der K-K Geol. Reich- 

 sanstalt, vol. 58, p. 729, textfigure 10. 



Tellina gatunensis Brown and Pilsbry, 191 1, Proc. Acad. Nat. Sci. 

 Phila., vol. 63, p. 368. 



This shell is extremely similiar to the recent M. elongata 

 Hanley of the Pacific coast of Panama and I have failed to find 

 any character which will distinguish the fossil shells from the 

 recent ones. Our shells were all collected loose near Hill 3, of 

 the Kanana River and w^ere probabl)^ derived from beds low in 

 the Gatun formation. 



Gatun Stage: loose, near Hill j , Banana River {Terry'). 



Macoma panamensls Dall, var. canalis, n. var, Plate 26, figure II 



Cf. Macoma [Psanimaconia) panamensls Dall, 1900, Proc. U. S. Nat, 

 Mus., vol. 23, p. 324, pi. 4, fig. 3. 



The Macoma pa?iamensis Dall was described from a left 

 valve dredged from 33 fathoms of water in Panama Bay. The 

 fossil shell, also a left valve from the Gatun of Mt. Hope, differs 

 most importantly from Dall's figure in being somewhat higher. 

 The shell is thin and extremely fragile, with the surface simply 

 scultured with the fine growth lines. The interior is concealed 

 so that the characters of the pallial sinus cannot be seen. The 

 specimens measures as follows: 



