20 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 72 



as suggested in the original description. The hinge is normal for 

 the subgenus Trachycardium, as this group is developed in the Upper 

 Cretaceous deposits of the Atlantic Coastal Plain. 



Geologic position. — Upper Cretaceous, upper part of the Peedee 

 formation, upper part of Exogyra costata zone. European equiva- 

 lent, upper Senonian (Maestrichtian). 



Figured specimens. — The new material figured is from the col- 

 lection made by Kellum in 1923, at the new quarries, a mile north- 

 east of Eocky Point station, Pender County, N. C, Cat. No. 73442 ; 

 seven additional specimens are in the collection. 



CARDIUM (TRACHYCARDIUM) MARSENSE, new species 



Plate 7, figs. 3, 3a, and 4 



Description. — Shell large, subcircular to broadly subovate in out- 

 line, a little longer than high, slightly oblique. Beaks moderately 

 prominent, incurved, approximate, nearly direct, situated slightly 

 in advance of the midlength. Umbonal ridge moderately prominent, 

 shell most inflated centrally, postero-dorsal slope steep, antero- 

 dorsal slope rounded, becoming steep above. Dimensions of the 

 holotype : Length, 49 ( ? ) mm. ; height, 46 mm. ; convexity, 16 mm. 



Hinge normal for the subgenus Trachycardium. Ligamental 

 groove short and deep. Inner surface smooth as preserved, adductor 

 scars faintly impressed, inner margin strongly crenulated. 



Dorsal margin broacQy arcuate, anterior and ventral margins 

 regularly rounded, posterior margin subangular below, truncated 

 above, trending obliquely forward and rounding rather sharply into 

 the postero-dorsal margin. 



Surface ornamented with 33 or 34 strongly developed ribs, 25 of 

 which are in front of the umbonal ridge. The ribs are sub-V-shaped 

 in cross section, subangular to rounded on the crests, and each rib 

 is scored on each side with a faint, narrow, longitudinal channel. 

 At the bottom of the depression between each rib is a closely ap- 

 pressed slit. On the anterior slope the crest of each rib is set with 

 irregularly spaced distinct nodes 2 to 4 mm. apart. The ribs on the 

 posterior slope grade from broadly V-shaped near the umbonal ridge 

 to almost flat near the postero-dorsal margin. 



Remarks. — This species has fewer and coarser ribs than either 

 C. donohuense Stephenson or G. longstreeti Weller, both of which 

 are closely related species occurring in the sa^e faunal zone in 

 North Carolina. The material consists of silicified shells, including 

 a large right valve, the holotype, broken and partly wanting in the 

 postero-ventral portion, a smaller more perfect right valve and 

 several more or less fragmentary right and left valves. 



