MOLLUSCA. 639 



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

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

 gin regularly rounded; basal margin nearly straight, curving 

 upward in front; postero-basal extremity angular; post-cardinal 

 margin concave. Valves strongly ventricose in front, com- 

 pressed behind, the ventral margin of the right valve overlap- 

 ping 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 umbonal slope; on trie left valve the umbonal ridge is obsolete.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 pro- 

 duced posteriorly as the shells, the muscular impressions are con- 

 spicuous the whole area of the casts between the muscular impres- 

 sions and the pallial line being strongly inflated. 



Remarks.* Johnson states that the specimens from Haddon- 

 field which were illustrated by Whitfield as C. fowlkei, are not that 

 species but C. bisulcata Con. An examination of the type speci- 

 mens in the collection of the Philadelphia Academy of Sciences 

 has confirmed the statement of Johnson. The species occurs in 

 abundance in the Clifrwood 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. 

 From one of these moulds, which is complete in its more essen- 

 tial parts, the cast used in the description of the shell was taken ; 

 the antero-basal region of the mould is lacking, but this portion 

 of the shell has been easily restored from the form of the internal 

 casts. 



Formation and locality. Oliffwood clay, Cliffwood Point 

 (185), near Matawan (107, 189) ; Merchantville clay-marl, near 

 Matawan (101), near Jamesburg (141), Lenola (163); Wood- 

 bury clay, Haddonfield (183). 



Geographic distribution. New Jersey, North Carolina, Mis- 

 sissippi, Arkansas. 



