Maryland Geological Survey 525 



The form described and figured by Conrad is not that described by 

 Gabb under the name of Area (Macrodon) eufalensis, but a distinct 

 species. Charles W. Johnson, 1 while listing the Cretaceous types in the 

 collection of the Philadelphia Academy of Natural Sciences, discovered 

 the error, and gave to Conrad's shell the name of Nemodon conradi. 



Nemodon is separated from Area by the development of both horizontal 

 and vertical teeth and from Cucullwa by the greater relative length of the 

 horizontal laminae. The genus is apparently confined to the Cretaceous. 



A. Shell thin; inner ventral margins simple. 



1. Base line parallel to dorsal margin Nemodon eufalensis 



2. Base line not parallel to the dorsal margin Nemodon stantoni 



B. Shell heavy; inner ventral margins crenate Nemodon cecilius 



Nemodon eufalensis (Gabb) Whitfield 

 Plate XX, Figs. 3, 4 



Area (Macrodon) eufalensis Gabb, 1860, Jour. Acad. Nat. Sci., Phila., 2d 



ser., vol. iv, p. 398, pi. lxviii, fig. 39 (incorrectly cited as 38). 

 Nemodon eufaulensis Whitfield, 1885, Mon. U. S. Geol. Survey, vol. ix, p. 83, 



pi. xii, figs. 3, 4. (Synonomy and fig. 5 excluded.) 

 Nemodon eufaulensis Johnson, 1905, Proc. Acad. Nat. Sci., Phila., vol. lvii, 



p. 9. 

 Nemodon eufaulensis Weller, 1907, Geol. Survey of New Jersey, Pal., vol. iv, 



p. 385, pi. xxx, figs. (?) 8-11 (casts only). 



Description. — " Inequilateral ; beaks large ; umbones large and slightly 

 grooved in the middle by a shallow sulcus, which extends nearly to the 

 base of the shell ; area very small ; hinge line straight, lower edge of the 

 hinge slightly curved; lateral teeth very long; anterior margin curved, 

 basal sinuous, posterior margin curved, upper part inclined anteriorly; 

 surface marked by numerous radiating ribs and smaller transverse lines. 



" Dimensions. — Length .-± in. ; width .5 in. 



"Locality. — Eufala, Alabama. Ripley Group. My collection." — Gabb, 

 1860. 



Shell transversely elliptical to subrhomboidal in outline, flexuous 

 medially, moderately inflated in the umbonal region, flattening toward 

 the ventral margin ; umbones broad, subangular, medially depressed, low, 



1 Johnson, 1905, Proc. Acad. Nat. Sci., Phila., p. 9. 

 34 



