MOLLUSCA. 727 



placed them. The species described by Whitfield as Triton 

 praecedens, however, seems to more nearly fit the genus Trachy- 

 triton than do these species which are placed in the genus. 



Trachytriton 7 atlanticum Whitfield. 

 Plate LXXXIV., Figs. 11-14. 



1892. Trachytriton atlcmticum Whiti., Pal. N. J., vol 2 (Monog. 

 U. S. G. S., vol. 18), p. 59, pi. 5, figs. 8-1 1. 



Description. — "Shell small, the casts seldom reaching a length 

 of more than an inch and a quarter; spire with an apical angle 

 of about 40° to 45" ; volutions four and a half to five in number, 

 rather convex and moderately distinct, the sutures in the cast 

 being distinct and the spaces left by the removal of the shell quite 

 considerable; last volution large, forming more than half the 

 entire length, and being as long below the point of greatest dia- 

 meter as the length O'f the spire above, giving an equally biconical 

 or fusiform feature to the cast, with a moderately long and some- 

 what curved beak and canal; aperture large, pointed above and 

 slightly extended below ; narrow-elliptical in outline, with the 

 outer margin rather more convex than the inner one ; lip of the 

 outer volution apparently slightly deflected; the surface of the 

 volutions have been marked by revolving lines, at least in the 

 lower part, as is shown by their reiTiains on the surfaces between 

 the volutions O'f the cast; and by proportionally strong, vertical 

 folds, three of which in each volution have been stronger than the 

 one or two intermediate ones, and have left their deeper impres- 

 sion both on the surface oi the cast and on the imprint of the 

 exterior, as seen between the whorls." (Whitfield.) 



Renua'ks. — In his illustrations of this species, Whitfield made 

 the vertical ribs of the shell much more conspicuous than they 

 really are upon the specimens. It does not seem to be altogether 

 certain that the generic reference of the species is correct, the 

 strongly defined pitted furrows upon the internal casts, left by 

 the denticulate internal varices, which are said by Meek^ to be 



' Rep. Inv. Cret. and Tert. Foss. Up. Mo., p. 303. 



