500 PROCEEDINGS OF THE ACADEMY OF [Dec, 



FAUNA OF THE GATUN FORMATION, ISTHMUS OF PANAMA-II. 

 BY AMOS P. BROWN AND HENRY A. PILSBRY. 



The collection reported in this paper was obtained by Professor 

 William B. Scott in 191 1. 1 It comprises materials from the follow- 

 ing sources: 



1. Fossils from the oyster-shell areas in the Black Swamp near 

 Mount Hope (Monkey Hill). This material consists of coral and 

 coralline fragments, with a considerable molluscan fauna, including 

 the oysters which are the distinguishing shells of these shell areas. 

 The bed lies about 4 feet above the present sea level, and is doubt- 

 less the same as that encountered in digging for sewers, etc., in 

 the streets of Colon. Among the Mollusca the recent species pre- 

 dominate, though some species found in this assemblage seem to 

 be extinct. It must be remembered, however, that the recent 

 fauna of this part of the coast, aside from the strictly littoral forms, 

 is very imperfectly known, and hence some of these supposedly 

 extinct forms may be found living. In any case, it does not seem 

 probable that this bed can be older than Pleistocene. The species 

 will be considered, along with those of lot 2, in another paper. 



2. From the oyster-shell areas in the black, unconsolidated mud, 

 unconformable on the Gatun Formation, found at the lower end of the 

 Gatun Locks. This mud extends from a few feet below sea level 

 to about 10 feet above it. The specimens collected consist of 

 shells of Ostrea with a large number of specimens of Congeria and 

 many barnacles. The other mollusks are not so plentiful as in lot 

 1, there are no corals or corallines, but it is evident from the im- 

 pressions on the shells that the oysters grew on mangroves or similar 

 plants. The species will be considered in another paper along with 

 those of the preceding collection. 



3. Fossils from the Gatun beds in the excavation of the Lower Locks 

 at Gatun. This bed was the source of most or all of the material 

 described in our former paper. 2 A number of additional species 



1 Acknowledgments are due to Mr. D. F. MacDonald. geologist of the 

 ('anal Commission, who collected a large part of the material and supplied the 

 data concerning it. 



Fauna of the Gatun Formation, Isthmus of Panama. Proc. A. N. S. Phila. t 

 1911, p. 336. 



