EXPLANATION OF THE FIGURES.* 



PLATE I. 



All figures on this plate are thirty times enlarged. 

 Glyphioceras incisum HYATT. 



Figs, i and 2. Protoconch. I, from above ; 2, from front. 

 Diameter, .46 mm. 



Figs. 3, 4, and 5. Protoconch of same or a nearly related spe- 

 cies from Scott County, Arkansas. 3, from above ; 4, from front ; 

 5, from side. 



Figs. 6, 7, and 8. Protoconch with first two sutures. 6, from 

 above ; 7, from front ; 8, from side. 



Figs. 9 and 10. Larval stage, diameter of .74jpm., protoconch 

 and one half of first whorl, showing the first four sutures, from 

 phylembryonic to the paranepionic substage. 9, from side , 10, 

 from front. 



Figs. II and 12. Larval stage, diameter of .92 mm., first 

 whorl, showing first eight sutures, and transitions from the me- 

 tanepionic (Anarcestes stage), through paranepionic ( 7\-in>fenis 

 stage) to ananeanic (Prionoceras stage). 11, frorn front ; 12, from 

 side. 



* From The Development of Glyphioceras and the Phylogeny of the 

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

 i, Geology, No. 3, Plate XIII. 



