180 SYSTEMATIC PALEONTOLOGY 



Creek, Potomac Creek (50 feet from top of bluff)^ 1 mile southeast of 

 Piscataway, La Plata, Upper Marlboro (gull}' southwest of town), 2 and 

 2^ miles above Popes Creek. 



Collections. — Maryland Geological Survey, U. S. National Museum, 

 PhiladeljDhia Academy of Natural Sciences. 



Family CRASSATELLITIDAE. 



Genus CRASSATELLITES Kruger. 



Ceassatellites alaepoemis (Conrad). 

 Plate XLI, Pigs. 1-8. 



Crassatella alaeformis Conrad, 1830, Jour. Acad. Nat. ScL Phila., voL vi, p. 228, 



pL X, fig. 1. 

 Crassatella alaeformis Morton, 1834, Syn. Org. Rem. Cretaceous Group, App., p. 7. 

 Crassatella capri- cranium Rogers, 1839, Trans. Am. PhiL See, new series, voL vi, 



p. 375, pL sxx, fig. 2. (Reprint: Geology of the Virginias, 1884, p. 672, 



pi. y, fig. 2.) 

 Crassatella alaeformis Conrad, 1846, Amer. Jour. Sci., ser. ii, voL i, p. 396, 



pL iii, fig. 3. 

 {?) Crassatella pal inula Conrad, 1846, Amer. Jour. Sci., ser. ii, vol. i, p. 896, pi. iv, 



fig. 1. 

 Crassatella alaeformis H. C. Lea, 1848, Proc. Acad. Nat. Sci. Phila., vol. iv, p. 98. 

 Crassatella capri-cranium H. C. Lea, 1848, Proc. Acad. Nat. Sci. Phila., vol. iv, p. 98. 

 Crassatella alaeformis d'Orbigny, 1850, Prodrome, vol. ii, p. 383. 

 Crassatella capri-cranium Conrad, 1865, Amer. Jour. Conch., vol. i, p. 10. 

 Crassatella alaeformis Conrad, 1865, Amer. Jour. Conch., vol. i, p. 10. 

 Crassatella alaeformis Conrad, 1866, Smith. Misc. Coll. (200), p. 5. 

 Crassatella capri-cranium Conrad, 1866, Smith. Misc. Coll. (200), p. 5. 

 Crassatella declivis Heilprin, 1880, Proc. U. S. Nat. Museum, vol. iii, pp. 151, 152, 



pi. facing p. 150, fig. 9. 

 Crassatella protexta de Gregorio, 1890, Auu. Geol. et Pal., pi. xxv, fig. 12. 

 Crassatella alaeformis Clark, 1895, Johns Hopkins Univ. Circ, vol. xv, p. 5. 

 Crassatella alaeformis Clark, 1896, Bull. 141, U. S. Geol. Survey, p. 81, pi. xxvii, 



figs. la-Ik. 

 {?) Crassatella palmula Clark, 1896, Bull. 141, U. S. Geol. Survey, p. 93. 

 Crassatella declivis Aldrich, 1897, Bull. Amer. Pal. No. 8, p. 4, pi. iii, figs. 1, la. 



Description. — " Shell transversely ovate oblong; anterior side ros- 

 trated; posterior side short and rounded; umbones transversely sulcated; 

 margin slightly crenulated within." Conrad, 1830. 



The variations in C. alaeformis Conrad are so great that in the ab- 

 sence of connecting forms one would be led to consider the existence of 

 several well-defined species. After a careful study of a large amount of 



