230 NEW FOSSIL, SHELLS 
species at present existing; in the Miocene the proportion is small; while, in the Post- 
Pliocene all are recent. According to Mr. Conrad, the per centage of still existing 
shells in the Miocene is about seventeen, but I am inclined to think that it will prove, 
on further investigation, to be smaller. It, however, cannot be relied on as a certain 
criterion, being extremely variable in different localities. Petersburg, Virginia, may be 
taken as an instance of one extreme: the following is a list of the fossils which have 
been found there, exclusive of those herein described. 
Dentalium thallus, . Con. Venus Rileyi, Con. | Fissurella redimicula, Say. 
6 attenuatum,. Say. “ — difformis, Say. Crepidula fornicata,. . “ 
Serpula granifera, . . “ Cardium sub-lineatum, . Con. “ costata, . Morton. 
I ) 
Balanus sp.? “ laqueatum, . . “ Dispotea ramosa, Con. 
Pholas ovalis, Say. Cardita granulata, Say. Natica duplicata, . . Say. 
Panopea reflexa, . . . * Cypricardia arata, . . . MGR wy 
aty 1 * 3 . . 
Mactra congesta, Con. Arca centenaria,. “ Acteon Wetherilli, Lea. 
Crassatella undulata, Say. jee dorien v Rotella nana, ‘i “a 
% 7 * . 
&“ melina, . Con. G;, aie ib Trochus philanthropus, Con 
ley ; 
akon baie? : ; ee, ve 
Corbula tacks nse § Pectnnculus subovatus, . ii Turritella eae, 
“ inequalis, . . F iy indenta, . Mi 
as a ag “ quinquerugatus, Con, se a 
Tellina equistriata,. . _ : “ plebeia, . Say. 
“ “ sh pulvinatus,’ Lamk. , 
Lucina speciosa, . . ; Pleurotoma pyrenoides, Con 
cs 3 * Nucula levis, Say. weir ifs 
conimact®, 1... * bi; ; Fasciolaria mutabilis, “ 
obliqtra, . ‘ ; 
dee 5:1) ar a Ch at Pyrula carica, Say. 
“ divaricata, Lamk. ama congregata,, . Con. “ — ganaliculata, 6“ 
66 i 66. 4 ‘ 
Astarte undulata, Say. corticosa, Fusus cinereus,. . . ‘ 
‘.. avata, Con Pecten eboreus, . by “  exilis, . Con 
- pea ‘ ee Pi 
“ ~ goncentrica, . “ “¢ — Madisonius, Say. Murex quadricostatus, . Say. 
Clathrodon Grayi,. . ‘“ Plicatula marginata, he Buccinum laqueatum, Con. 
Cytherea reposta, . . “ Perna torta, . : aa 6“ porcinum, “ 
“ convexa, . Say. Ostrea Virginiana? var. tmel, Marginella perpusilla, . * 
Artemis acetabulum, Con. Capulus lugubris, Con limatula, Oh 
We have here sixty-eight species, in addition to one hundred and five which I shall 
describe in this paper, and which I consider as hitherto unknown, or in all, one hundred 
and seventy-three. Now, of these, but nine can be identified with existing shells, 
namely, 
Lucina divaricata, 
Artemis acetabulum, 
Ostrea Virginiana? 
Crepidula fornicata, 
Natica heros? 
“ duplicata, 
Pyrula carica, 
hig eanaliculata, 
Fusus cinereus. 
and of these, two appear to me doubtful, namely, Natica heros, and Ostrea Virginiana. 
Considering them, however, as the recent species, this gives us about five per cent. 
of still existing shells. It appears almost absurd to compare this with the Miocene 
of Dax, the best characterized in Hurope, which, by the tables of Dr. Grateloup, con- 
*Jn the first number of the “ Fossil Shells of the Tertiary of North America,’ Mr. Conrad has described and 
figured a shell as the Pect. pulvinatus, Lam. But, after comparing it with a number of specimens of that species, 
and with Deshayes’ figures, I am forced to consider it as specifically distinct. I, therefore, propose to name it 
P. ELEPHANTOPUS, 
