1919.] NATURAL SCIENCES OF PHILADELPHIA. 45 



the dorsal margin. Pallial line punctate, broadly arcuate, remote 

 from the ventral margin. 



Dimensions. — Altitude, 33.0 mm. Latitude, 21.0 mm. Diam- 

 eter, 6.0 mm. 



Type Locality. — Yorktown, York County, Virginia. Yorktown 

 Formation. 



Observations. — Though Pandora prodromos does not occur at 

 Mayesville, the species has been described in this paper in order 

 to bring out the close relationship which apparently exists between 

 the Tertiary Pandoras of the East Coast and the Recent. In the 

 Recent, the sub-genus Clidiophora is represented south of the 

 Hatteras axis by the delicate, alate little, form, Pandora trilineata 

 Say. The northern analogue, P. gouldiana Dall, is larger, heavier, 

 and rudely rectangular in outline. The differences between the 

 northern and the southern analogues have apparently been inherited 

 from their Tertiary precursors, Pandora tuomeyi new species of 

 the Duplin and Waccamaw faunas and Pandora prodromos of 

 the Yorktown. P. prodromos is a little higher, relatively than 

 P. goiddiana Dall, and the posterior margin is not so sharply 

 constricted below the sub-marginal keel. The dentition of the 

 Tertiary species is very much heavier than that of the Recent. 

 The middle and posterior cardinals of the right valve and the 

 anterior cardinal of the left are, in P. gouldiana Dall, compressed 

 into little more than linear ridges, while in P. prodromos they are 

 decidedly heavy and robust. P. prodromos is neither so large 

 nor so heavy, however, as the co-existent P. crassidens Conrad; 

 there is no trace retained of the linear radial sculpture which 

 characterizes crassidens, and the dorsal portion of the anterior 

 cardinal of the left valve is not expanded into a well defined flange 

 as in Conrad's species. 



Distrihulion. — Yorktown Formation. Yorktown, York County; 

 \\ miles north of Suffolk, 1^ miles east of Suffolk, 1 mile northeast 

 of Suffolk, 1 mile west of Suffolk, and ^ mile below the water works 

 dam at Suffolk, Nansemond County, Virginia. Tar Ferry, on 

 Wiccacon Creek opposite Harrelsville, Hertford County, North 

 Carolina. 



Collections. — U. S. National Museum. Johns Hopkins Uni- 

 versity. Academy of Natural Sciences of Philadelphia. 



Pandora (Clidiophora) tuomeyi new species. Plate IV, flgs. S, 10, 13. 



Pandora trilineata Say, 1856, Tuomey and Holmes, Pleiocene Fossils South 

 Carolina, p. 76, pi. xx, fig. 13. 



