494 PROCEEDINGS OF THE ACADEMY OF [July, 



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

 mud, uncomjormable on the Gatun Formation at the lower (north) end 

 of the Gatun Locks. — This deposit of mud extends from a few feet 

 below sea level to about 10 feet above it at this point. The black 

 character of the deposit and the finding of definite vegetable remains 

 in it, coupled with the observation that the oysters grew attached to 

 mangroves or similar plants, shows that this was a deposit accumu- 

 lated at the head of a bay or in an estuary. From the clean condition 

 in which this material reached us, it seems likely that this collection 

 was the result of the screening of the discharge from a suction dredge. 

 This would also account for the absence of all small specimens from 

 the collection. The species present indicate shallow, probably 

 brackish, water conditions. The most notable species is the oyster 

 (evidently growing attached to plants) and the great number of 

 Congeria shells. The oyster shells are often seen to be covered with 

 barnacles. Besides the one species of barnacle, there were three 

 species of Gastropods and five species of Pelecypods. One of the 

 Gastropods, Neritina virginea Lam., has the color pattern of the shell 

 beautifully preserved. This deposit is probably more recent than 

 that at Mount Hope, but is probably, like it. Pleistocene. 



We are indebted to Mr. J. B. Henderson, of Washington, for 

 working over and determining a large part of the species listed below. 



List of Species from the Oyster-shell Layers from the 

 Black Swamp near Mount Hope. — Collection L 



Balanus eburneus Gould. 



Tornatina canalicidata (Say). R.^ 



Cylichnella bidentata (Orb.). 



Atys Sander soni Dall. 



Bullaria occidentalis (A. Ad.). C. 



Haminea canalis Dall. 



Haminea antillarum (Orb.). R. 



Terebra spei n. sp. 



Conus proteus Hwass. R. 



Drillia leucocyma Dall. 



Drillia ostrearum Stearns. 



Drillia harfordiana (Reeve), var. colonensis n. v. R. 



Clathurella jewettii Stearns. R. 



Cythara balteata (Reeve). 



Cythara biconica (C. B. Ad.). C. 



Marinula colonia Dall. R. 



OUvella myrmecoon Dall. C. 



' The abundance or rarity of the species is indicated by the letters R. (rare) 

 nd C. (common). 



