712 SYSTEMATIC PALEONTOLOGY 



Description. " Shell ovate-acute, equilateral, concentrically striated, 

 with two or three distant large concentric furrows; posterior extremity 

 acute." Conrad, 1875. 



Type Locality. Snow Hill, North Carolina. 



" The dimensions of a partially restored specimen, a plaster cast taken 

 from a natural mould, are : Length 13.5 mm., height 8 mm., thickness 

 6.5 mm. Shell subcuneate behind, full and rounded in front. Beaks 

 small, incurved, situated back of the middle, pointing posteriorly. Antero- 

 cardinal margin long, straight near the beaks and curving gently down- 

 ward in front, subparallel with the basal margin ; anterior margin regu- 

 larly rounded ; basal margin nearly straight, curving upward in front ; 

 postero-basal extremity angular; post-cardinal margin concave. Valves 

 strongly ventricose in front, compressed behind, the ventral margin of 

 the right valve overlapping that of the left and its posterior extremity 

 more produced, beaks of the two valves subequal ; an angular umbonal 

 ridge is present on the right valve, with a narrow, slightly concave post- 

 umbonal slope; on the left valve the umbonal ridge is obsolete. Surface 

 of the valves marked by rather fine, concentric lines of growth. 



" Perfect internal casts are subcuneate, but not so greatly produced 

 posteriorly as the shells, the muscular impressions are conspicuous, the 

 whole area of the casts between the muscular impressions and the pallia! 

 line being strongly inflated. Johnson states that the specimens from 

 Haddonfield, which were illustrated by Whitfield as (.'. foulkei, are not that 

 species but C. bisulcata Conrad. An examination of the type specimens in 

 the collection of the Philadelphia Academy of Natural Sciences has con- 

 firmed the statement of Johnson. The species occurs in abundance in the 

 Cliff wood clays, and it seems to be one of the most characteristic species in 

 the fauna of that horizon. They occur usually in the form of internal 

 casts, some of which are very perfect, and some good moulds of the 

 exterior have been found." Weller, 1907. 



The species is represented in Maryland by a single cast apparently of an 

 immature individual. 



Occurrence. MAT AW AN FORMATION. Three-quarters of a mile south- 

 cast of Ulmstead Point, Anne Arundel County. 



