538 CRETACEOUS PALEONTOLOGY. 



incurved, and do not extend as far forward as the extreme 

 anterior margin of the shell. The strong concentric rugosities 

 of the shell are. not impressed upon the surface of the casts, but 

 the muscular impressions are large and strong, the anterior one 

 especially being much elevated above the general surface of the 

 cast, indicating the presence of a very deeply impressed anterior 

 muscular attachment. 



Remarks. There seems to be nothing about this shell which 

 might not be an extreme condition of the much smaller V . con- 

 radi. The external characters have been described above from 

 a plaster cast taken from a very perfect mould of the outside of 

 a large shell of which the internal cast is also perfectly preserved. 

 A portion taken from the apical part of the shell of the size of 

 the ordinary specimens of V. conradi from the lower beds, could 

 not be distinguished from members of that species. It has been 

 thought best to retain V. trigona as a distinct species, however, 

 because of its stratigraphic relations, it being nowhere observed 

 in beds beneath the Navesink marl. In the lower beds, shells 

 with the characters of V. conradi seem to be fully adult, and do- 

 not seem to develop further, but in the higher beds we find V. 

 trigona a direct genetic successor of V. conradi, the development 

 of whose shell continues much further than the shell of the earlier 

 form. It is possible that the specimens from the higher beds. 

 which have been identified as V. conradi, should rather be con- 

 sidered as the young of V . trigona, since it would be difficult or 

 perhaps impossible to distinguish between the young of the later 

 and the adults of the earlier species. 



Formation and locality. Navesink marl, near Walnford 

 (i47 4 , I48 4 , 149); Tinton beds. Beers Hill cut, south of Key- 

 port (i2 9 5 ). 



Geographic distribution. New Jersey, Alabama, Texas. 



Veniella ? rhomboidea Conrad. 

 Plate LVIIL, Figs. 22-24. 



1853. Venilia ? rhomboidea Con., Jour. Acad. Nat. Sci. Phil. 



2d sen, vol. 2, p. 275, pi. 24, fig. 7. 

 1861. Venilia rhomboidea Gabb, Synop. Moll. Cret. Form., p. 



234 (178). 



