1852.] 199 



many littoral genera as Pleurotoma, the species of which are very abundant in 

 specimens, TurritcUa, Natica, Terebra, Oliva, and various others, indicate shallow 

 water, and the abundance of comminuted shells and waterworn specimens attest 

 the vicinity of a sea beach. 



The well known Miocene deposits are remarkably unlike that of Vicksburg, 

 in the abundance of large species of Venus, Fulgur, Perna, and Panopoea, some of 

 which genera, with their peculiar species in every latitude, render the Miocene 

 period recognizable at a glance. Indeed it is singular that the distinctive cha- 

 racter of this formation should be so strongly marked over an extent of 400 

 miles north and south. Even the Venus alveata, a common Maryland fossil, 

 seems to be abundant beneath the level of the sea, on Sullivan's Island, near 

 Charleston, and another Maryland fossil, which I have named Ecphora -i-costata^ 

 {Fu^us A-costaius oi Say,) was found on the beach of St. Simon's Island, Georgia. 

 Both localities are south of the latitude of Vicksburg, the Georgia one nearly a 

 degree farther south. The researches of Mr. Tuomey, in South Carolina, have 

 brought to light at least 26 species, which are known to occur as far north as 

 St. Mary's river, Maryland. From this comparison of groups it seems obvious 

 that the Vicksburg deposit must be of earlier origin than the fossiliferous Ter- 

 tiary strata of Maryland, Virginia, North and South Carolina, which seem all 

 to be of one geological era, though Mr. Tuomey refers those of South Carolina 

 to the Older Pliocene period. Whether the Mississippi formation should be 

 termed an Older Miocene or a Newer Eocene, may yet be doubtful, but that it 

 is intermediate between the Lower and Middle Tertiary, and differing widel/ 

 from either in the period of its deposition, is obvious. 



A careful exploration of the St. Domingo locality will probably clear up all 

 doubts on the subject. 



In conclusion, I may observe, that besides the Turbinella Wilsoni and Oniscia 

 harpula, the Cassidaria Icevigata, Forbes, is identical with my C. liniea, thus 

 giving three species common to the Vicksburg and St. Domingo groups. 



Notes on Shells, luith Descrtpttons of new Species. 



By T. A. Conrad. 

 Cryptodon, Con. 



The name of this genus, founded on i/ya cancellata, having been previously 

 applied by Turton to another group of bivalves, and now adopted by some 

 conchologists, it is necessary to change it, and I therefore propose 



SCHIZOTH.^RUS, 



in allusion to the profound channel which indents the hinge of both sides of 

 the cardinal teeth. 



SCHIZOTH^RUS NUTTALLII. 



Cryptodon Nuttallii, Con., Journ. A. N. S. vol. 1, p. 325, pi. 18, fig. 1. 



Unio. 



Unio Mortoni, Con., Dec. 1835. 

 U. turgidus, Lea, 1837. 



Mr. Lea's description of this species was read at a meeting of the Philosophi- 

 cal Society in Dec. 1834, but not published before 1837. 



Miocene species ? 



OSTRBA. 



Ostrea Titan. Elliptical or oblong ; extremity thick and ponderous, contracted 

 towards the hinge; ligament cavity profound ; upper valve slightly arched ; 

 surface coarsely marked. Length 10^ inches. 



