1880.] NATURAL SCIENCES OF PHILADELPHIA. 25 



26 Pholacloin3'a abrupta,t 30 Venus aloeata, 



27 Pliolas arcuata, 31 *' Mortoni^ 



(= P. costata), 32 " tetrica,t 



28 Saxicava rugosa,-f 33 " mercenaria^f 



29 Solen ensis ?f 34 " inoceriformis.f 



Note. — The italicized names represent species supposed to be 

 identical with living forms ; those (in the Patuxent group) fol- 

 lowed by the letters St. M. and E., species common to St. Mary's 

 and to Easton (Choptank River); and those (in the St. Mary's 

 group) followed by a f , species peculiar to the locality. 



A comparison of the foregoing lists will show at a glance, that 

 of the thirt3^-four bivalves belonging to the older formations, at 

 most only three (or 9 per cent.) are found to be living forms 

 {Pholas ovalis [= P. costata?^^ Venus alveata, and Venus Mortoni), 

 and that only six (18 per cent.) and seven (21 per cent.) are corn- 

 common respectively to the Patuxent and St. Mary's exposures , 

 viz. : 



To Patuxent. To St. Mary's. 



Artemis acetabulum,* Artemis acetabulum, 



Corbula idonea, Corbula idonea, 



Pholas ovalis,* Pholas arcuata (= costata), 



Panopaea porrecta, Panopsea porrecta, 



Pecten Madisonius, Pecten Madisonius, 



Venus Mortoni, Venus Mortoni, 



" alveata.* 



* There appears to be much confusion regarding the species of Artemin 

 found fossil in the Atlantic tertiary deposits, and their relation to the 

 forms now living on the Florida coast. In 1833 ("Fossil Shells of 

 the Tertiary Formations," p. 20) Conrad characterized the species A. 

 acetabulum, which appears to have been until then confounded with the 

 A. concentrica, Con., non Borni^. discus, Reeve, "Conchologia Iconica," 

 vol. vi, sp. 9), inhabiting the southern coast. No mention is there made 

 of its being found also in a recent state, but subsequently, 1838 ("Fossils 

 of the Medial Tertiary Formations," p. 29), we find the following statement : 

 "This fine species is very common in the localities named, and also occurs 

 recent on the Florida coast." In the list of shells inhabiting the Floi-ida 

 coast, prepared by the same author in 1846 (A. J. Science, 2d series, ii, 

 p. 393), only two species of Artemis are catalogued, A. elegans and A. con- 

 centrica, and it therefore appears highly probable that the statement con- 

 sidering A. acetabulum also as a living form was founded on a misconcep- 

 tion, the more especially, as an examination of the recent shells in the 

 3 



