364 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



volutions, just below the suture, the revolving impressed lines are more 

 closely arranged, and the spaces between, of course, proportionally narrower, 

 or merely linear. There seem to be no indications of vertical folds, or costae, 

 on any of the volutions; though no specimens have yet been seen with the 

 surface well preserved on the upper part of the spire. 



This little shell was originally referred doubtfully to the genus Fascio- 

 laria ; but its very small size, and the higher position of the plaits on its 

 columella, as well as its apparent want of crenulations on the inner side of its 

 outer lip, all seem to indicate much nearer relations to the other shells here 

 grouped under the name Piestochilus, the most important distinguishing char- 

 acters of which were then unknown. It seems to be quite rare. 



Locality and position.- — Moreau River; from the Fox Hills group of the 



Upper Missouri Cretaceous series. 



» 



? Subgenus MESORHYTIS. 

 Fasciolaria! (Mesorhytis) gracilcnta, Meek. 



F'g- 45 - Shell rather elongate-fusiform ; spire produced, con- 



ical, near])' equaling the length of the aperture and canal ; 

 volutions six or seven, slightly convex, each ornamented 

 by about twenty small, nearly straight, vertical folds, or 

 costse, that become less distinct, or almost obsolete, 

 toward the aperture on the body-volution, which is nar- 

 row, and tapers gradually below into the slender, pro- 

 FascioUria'! (Mesortytis) duced, nearly straight canal; columella very slightly 

 graaienta. arcuate above, and almost straight and scarcely at all 



twisted below, bearing, opposite the middle of the aperture, three rather 

 strong, moderately oblique plaits, that scarcely come to view when the aper- 

 ture is even partly filled with foreign matter; aperture narrow, or lance-oval, 

 being angular above, slightly more convex on the outer than the inner side, 

 and tapering gradually into the canal below ; surface ornamented by fine lines 

 of growth, that do not curve more than sufficient to indicate a very slight 

 sinuosity in the outline of the outer lip above, and are crossed by numerous 

 fine, irregular, revolving striee. 



Length, about 1.25 inches; breadth, 0.35 inch; slopes of spire nearly 

 straight, with a divergence of about 32°. 



The specimens of this shell in our collections were discovered in break- 



