670 SYSTEMATIC PALEONTOLOGY 



Description. " Shell below a medium size, irregularly trapezoidal or 

 subtriangular in outline, highly ventricose and sharply angular along the 

 posterior umbonal ridge, with a nearly vertical postero-cardinal slope. 

 Beaks large, prominent and attenuated, projecting considerably above the 

 hinge line. Anterior side of the shell short and regularly rounded ; pos- 

 terior vertically truncate and the basal line oblique, being prolonged 

 below toward the posterior umbonal angle. Surface marked, on the body 

 of the shell at least, by very fine, semi-obsolete, radiating striae, the pos- 

 terior cardinal slope not showing evidences of striations on the cast, the 

 only condition under which it has been observed. Hinge features 

 unknown. 



" The shell has all the generic features of the genus Fragum, as far as 

 can be determined from the external form, while the striations of the sur- 

 face are much finer than is usually the case; but no ornamentation can 

 be detected on the striations, and the features of the hinge are not visible. 

 It is the only form of similar character yet known to me in the formations 

 of the state." Whitfield, 1885. 



Type, Locality. Marlborough, New Jersey. 



"The dimensions of an internal cast are: Height 44 mm., width 

 37 mm., thickness 35 mm. Large examples sometimes attain a height of 

 over 60 mm. Shell irregularly subovate in lateral view and cordate in 

 end view. Hinge line arcuate; anterior and basal margins, from the 

 extremity of the hinge line to the middle of the basal margin, describing 

 a nearly regular, arcuate curve; postero-basal margin curving more 

 sharply around the postero-basal extremity of the shell into the posterior 

 margin; posterior margin -much straighter than the anterior, usually 

 gently convex but sometimes nearly or quite straight. Beaks situated at 

 about the middle of the hinge line, rather prominent, elevated, pointed 

 and incurved, considerably more prominent in the casts than in the speci- 

 mens with the shell preserved. Valves gibbous, most prominent, but not 

 angular, along a line from the beaks to the postero-basal extremity, the 

 posterior slope more abrupt than the anterior. Muscular impressions 

 rather large, the posterior one scarcely impressed and often scarcely dis- 



