230 



NORTH AMERICAN INDEX FOSSILS. 



inserted in guard, much shorter than it. Jurassic (Lower Lias)- 

 Cretacic. 



405. B. (Megateuthis) densus. (Fig. 15 12.) Jurassic. 



Guard large, up to four inches long below phragmocone, and 



nearly one inch in diameter ; subcylindrical, ovate, or oval in sec- 



FlG. 15 1 1. Atraciites philippic the 

 phragmocone in part of guard (a), X f> 

 and separate (<^),X I- (After Hyatt and 

 Smith.) 



Fig. 15 1 2. Belemnites densus, 

 X |. (After Whitfield, Pal. Black 

 Hills.) 



tion; sometimes obscurely subquadrangular ; phragmocone short, 

 rapidly expanding; apex subcentral in guard; septa numerous, 

 regularly concave. 



Jurassic of Dakota and Utah. 



406. B. (Belemnopsis) impressus Gabb. (Fig. 1513, a-c.) 



Comanchic. 



Large, robust, subcylindrical, tapering for about one fourth of its 

 length to blunt point ; ventral side with wide, deep furrow, deepest 

 at about apex of phragmocone and fading to end of guard. 



Very abundant in Upper Knoxville and basal Horsetown of 

 California. 



