EXPLANATION OF THE FIGURES.* 

 PLATE II. 



All figures on this plate are fifteen times enlarged, except Fig. 9, 

 which is once and a half its natural size. 



Glyphioceras incisum HYATT. 



Figs, i and 2. Adolescent stage, one and three fourths whorls, 

 diameter of 1.29 mm., last whorl is ananeanic (Prionoceras stage) 

 and shows transition from paranepionic. i, front ; 2, side. 



Figs. 3 and 4. Adolescent stage, diameter of 1.37 mm., one 

 and seven eighths whorls, Prionoceras stage. 3, from front ; 4, 

 from side. 



Figs. 5 and 6. Adolescent stage, diameter of 1.64 mm., two 

 and one eighth whorls, Prionoceras stage. 5, from front ; 6, from 

 side. 



Figs. 7 and 8. End of adolescent stage, diameter of 2.25 mm., 

 two and three fourths whorls ; transition from Prionoceras to 

 Glyphioceras in the division of the ventral lobe, and beginning 

 rounding of the whorl. 7, side view ; 8, front view. 



Fig. 9. Early adult stage, diameter of 15 mm., once and a 

 half enlarged. 



* From The Development of Glyphioceras and the Phylogeny of the 

 Glyphioceratidae, by J. P. Smith. Proc. Calif. Acad. Sci., third series, vol. 

 i, Geology, No. 3, Plate XIV. 



