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 man}^ other respects. 

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

 may occur. 



Gatu7i Stage; Hill No. j, Banana River. 

 Rio Be ley. 



Subgenus PSAMiViACOiVlA, Dall 



Macoma gatunensis Toula Plate 26, figure 13 



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

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



Tellina gatuneiisis 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 Banana River and were probably derived from beds low in 

 the Gatun formation. 



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



Macoma panamensis Dall, var. canalis, n. var, Plate 26, figure 11 



Cf. Macoma {Psamniacoma) panamensis Dall, 1900, Proc. U. S. Nat, 

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



The Macofna panamensis Dall was described from a left 

 valve dredged from 33 fathoms of water in Panama Ba}^ 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 

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

 specimens measures as follows: 



