G68 SYSTEMATIC PALEONTOLOGY 



her). Exogyra ponderosa zone, Mortoniceras subzone, Blufftown, Geor- 

 gia; Prentiss County, Mississippi. Ripley Formation. Exogyra costata 

 zone, Georgia; Eufaula, Alabama; Lee, Union and Tippah counties, Mis- 

 sissippi. Extreme top of zone, Pataula Creek, Georgia. Selma Forma- 

 tion. Exogyra costata zone, Wilcox County, Alabama; east-central Mis- 

 sissippi. 



CAEDIUM DUMOSUM Conrad 



Cardium (Criocardium) dumosum Conrad, 1870, Am. Jour. Conch., vol. vi, 



p. 75. 

 Cardium (Criocardium) dumosum Whitfleld, 1885, Mon. U. S. Geol. Survey, 



vol. ix, p. 133, pi. xx, figs. 9 and ? 13 (not figs. 10-12). 

 Cardium dumosum Johnson, 1905, Proc. Acad. Nat. Sci., Phila., p. 15. 

 Cardium dumosum Weller, 1907, Geol. Survey of New Jersey, Pal., vol. iv, 



p. 590, pi. Ixv, figs. 7-10. 



Description. " Cordate equilateral, ventricose ; umbo broad ; summit 

 very prominent; ribs very numerous, small, closely arranged, convex; 

 interstices furnished with numerous long slender spines ; posterior mar- 

 gin subtruncated or slightly convex ; height 1-J inch ; length the same."- 

 Conrad, 1870. 



Type Locality. Haddonfield, New Jersey. 



The spinose cardiums, C. Jciimmeli Weller, C. dumosum Conrad and 

 C. tenuistriatum Whitfield, are represented in Maryland merely by casts of 

 the interior or fragments of casts of the exterior. Weller has admirably 

 differentiated the three species from material in a better state of preserva- 

 tion than any available from Maryland, and his diagnoses have been 

 quoted at considerable length. 



" The dimensions of a large individual are : Height 18 mm., width 

 18 mm., convexity of one valve 6 mm. Shell subcircular in outline, but 

 slightly inequilateral, moderately convex. Beaks situated at about the 

 middle of the hinge line, rather small and incurved ; umbones prominent, 

 the anterior and posterior cardinal slopes about equally steep ; shell slightly 

 compressed at both cardinal extremities. Surface of the shell marked 

 with about fifty-four rounded radiating costa?, with interspaces of about 

 equal width; from the bottom of every third interspace on the central 

 portion of the shell there arises a row of laterally flattened spines 1 to 



