124 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 30 Ser. 



EXPLANATION OF THE FIGURES. 



Plate XIII. 



All figures on this plate are forty times enlarged. 



Glyphioceras incisum Hyatt. 



Figs. I, 2. Protoconch. i, from above; 2, from front. Diameter 0.46 

 mm. 



Figs. 3, 4, 5. Protoconch of same or a nearly related species from Scott 

 County, Arkansas. 3, from above; 4, from front; 5, from side. 



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

 front; 8, from side. 



Figs. 9, 10, Larval stage, diameter of 0.74 mm., 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. IT, 12. Larval stage, diameter of 0.92 mm., first whorl, showing first 

 eight sutures, and transitions from the metanepionic {Atiarcestes stage), 

 through paranepionic ( Tornoceras stage) to ananeanic (Prionoceras) stage. 

 II, from front; 12, from side. 



