234 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



EXPLANATION OF PLATE XXV. 



Figs. I, 2. Placenticeras calif ornicum, adolescent, perisphinctoid stage, two 



and five-sixteenths coils, diameter 3.32 mm.; 10 times enlarged. 



Henley, California. 

 Fig. 3. P. califoriiicuni, adolescent, transition from cosmoceran to the 



Hoplites stage; three coils, diameter 8 mm. ; 2.7 times enlarged. 



Henley, California. 

 Figs. 4, 5. P. californicum, adolescent, typical Hoplites stage, three and 



five-eighths coils, diameter 14 mm.; twice enlarged. Henley, 



California. 

 Figs. 6, 7. P. californicutn, adolescent, Hoplites stage, four coils, diameter 



22 mm.; twice enlarged. Arroyo del Vall6, Alameda County, 



California. 

 Fig. 8. P. californictim, transition from Hoplites to Placenticeras, four 



and a half coils, diameter 34.50 mm.; twice enlarged. Henley, 



California. 

 Figs. 9, 10. P. pacific uni, &nA oi Hoplites stage, four coils, diameter 20.5 



mm.; 2.7 times enlarged. Arroyo del Vall6, California. 

 Fig. II. P. pacificum, transition to Placenticeras, diameter 47 mm., four 



and five-sixths coils; natural size. Henley, California. 



