1881.] NATURAL SCIENCES OF PHILADELPHIA. 445 



are of scientific value, affirms tliat the majorit}' of the fossil mol- 

 Insca are of the Claiborne type, and he conseqnenth^ correlates 

 the beds containing them in a general way with those exposed on 

 the Alabama River, although without specially indicating with 

 what portion of the Claiborne section they were supposed to cor- 

 respond. Indeed, about the onl}^ fossils obtained from tlie Mary- 

 land localities which can in an}' way be said to be either charac- 

 teristic of or peculiar to them are Fanopea elongata, Pholadomya 

 Mai-ylandica^ Pholas ^le/z'osa, Cucullsea {Latiarca) gigantea, 

 Osfrea comprensirostra, and one or two doubtful species of Cras- 

 satella. All the species here named, if we except the doubtful 

 Grafisatellas and Ostrea compressirostra are good species, and if 

 we further deduct Cucullsea gigantea^ the onl}^ Eocene species of 

 the genera to which they belong thus far discovered in the eastern 

 or southern United States. On the whole, therefore, the^^ afford 

 little or no clue to the exact determination of the age of the 

 deposits in which they occur. It is true that an examination of 

 the homotaxial deposits of Europe shows the genera Pholadomya 

 and Panopea to be more especially characteristic of the lower or 

 even lowermost horizons of the Eocene series, as in the English 

 and French basins, but no special inference can be drawn from 

 this circumstance, since the species are not the same, and the 

 genera survived through tlie succeeding periods to the present 

 day. In the case of Osti^ea compressirostra, however, we have a 

 much more tangible point. The species, first described and 

 figured b}^ Sa}^ (Journal of the Academ}' of Natural Sciences, iv, 

 p. 133), is certainl}"^ very intimately related to the Ostrea Bellova- 

 cina of Lamarck, and apparentl}^ undistinguishable from certain 

 varieties of that species.^ Now this species, although not exclu- 

 sivel}' restricted to the lowest Eocene beds, is nevertheless highly 

 characteristic of the Thanet sands, below the London Clay proper 

 and also below what was formerl}^ designated as the " Plastic 

 Clay " series, where it constitutes a true basement accumulation ; 

 and it holds almost precisely the same relation to the beds of the 

 Paris basin, where, according to Deshayes {Animaux s. Vertebres^ 



^ The distinguishing characters of the beaks pointed out by Say do not 

 seem to hold in many instances, as is proved by specimens of the G. Bello- 

 vacina from the " London Clay" of Bognor, England, in the collections of 

 the Academy, which do not dift'er as much from certain American speci- 

 mens as these last do among themselves. 



