32 PROCEEDINGS OF THE ACADEMY OF [1880. 



Bivalves. 



Ostrea Mauricensis, Astarte Thomasii, 



" percrassa, Venus Ducatellii, 



Plicatula densata, Periploma alta, 



Carditamera aculeata, Corbula elevata, 



" arata, Saxicava myaeformis. 



Craseatella melina, 



Four species of the above are also found in Maryland, three of 

 which, Ostrea percrassa, Crassatella melina, and Corbula elevata, 

 are found, I believe, exclusively in the deposits designated as 

 those of the older period. None are recent forms. 



The small percentage of living forms occurring in the " older 

 deposits," as compared with that of the " newer," leaves little 

 doubt for the inference that the deposits in question were formed 

 at two different periods, the latest of which clearly belongs to the 

 Miocene. A comparative examination of some of the peculiar 

 fossil forms of the older deposits, together with the extremely low 

 percentage of living forms, seems to indicate an age moi-e nearh' 

 Oligocene than Miocene, although perhaps not a single Eocene 

 species is represented. This last fact need not surprise us, howcA^er? 

 as the relationship of the Oligocene to the Miocene appears to be 

 greater in almost all the localities of its representation than to the 

 Eocene. The Eocene, moreover, of Maryland is represented only 

 by a very limited number of fossils, and Conrad, himself, has called 

 attention to the fact, that there appears to exist a greater amount 

 of difference between the Eocene and Miocene formations than 

 obtains between the Secondary and Tertiary, or between the 

 Devonian and Carboniferous systems (B. N. I., p. 177). The fol- 

 lowing comparison may serve to throw some light upon the rela- 

 tive age of the deposits in question : 



Perna maxillata, Lam. 



This species agrees thoroughly with the figure and description 

 of the same given b}' Goldfuss in the " Pectrefacta Germanise " 

 (vol. ii, p. 106), and to which the locality Weinheim (Oligocene) 

 is assigned. The sub-Apennine species, formerly classed under 

 the same name, is considered by Deshaj^es to be distinct, and he 

 has applied to it the specific name of Soldanii (Lamarck, '"'■ Animaux 

 sans Vertebres,"" 2d ed., vol. vii, p. 79). A second species of Perna, 

 the P. Sandbergeri, Desh., also occurs in the Oligocene locality of 



