EXPLANATION OF THE FIGURES.* 
PuiaTE I, 
All figures on this plate are thirty times enlarged. 
- Glyphioceras incisum AYAtTT. 
Figs. 1 and 2.—Protoconch. 1, 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 .74 mm., protoconch 
and one half of first whorl, showing the first four sutures, from 
phylembryonic to the paranepionic substage. 9, from side, Io, 
from front. 
Figs. 11 and 12.—Larval stage, diameter of .92 mm., first 
whorl, showing first eight sutures, and transitions from the me- 
tanepionic (Avnarcestes stage), through paranepionic (7ornoceras 
stage) to ananeanic (Prionoceras stage). 11, from front; 12, from 
side. 
* From The Development of Glyphioceras and the Phylogeny of the 
Glyphioceratide, by J. P. Smith. Proc. Calif. Acad. Sci., third series, vol. 
i, Geology, No. 3, Plate XIII. 
