l6o CALIFORNIA ACADEMY OF SCIENCES. [Proc. ,^d Ser. 



EXPLANATION OF THE FIGURES. 



Plate XX. 



Development of the Septa oi Phylloceras onoense Stanton. 



Fig. I. Protoconch, with the first four septa, drawn as if unrolled, forty 

 times enlarged, transition from phylembryonic, through ana-, 

 to meta-, to para-nepionic. 



Fig. 2. Diam. 0.87 mm., one and one-sixth coils, forty times enlarged. 



Fig. 3. Diam. 1.42 mm., one and three-fourths coils, transition from larval 

 to adolescent stage, forty times enlarged. 



Fig. 4. Diam. 1.90 mm., two and one-sixth coils, forty times enlarged ; ado- 

 lescent. 



Fig. 5. Diam. 2.46 mm., twenty times enlarged. 



Fig. 6. Diam. 4.50 mm., thirteen times enlarged. 



Fig. 7. Diam. 7.00 mm., thirteen times enlarged. 



Fig. 8. Diam. 35.00 mm., natural size, adult stage; traced from photo- 

 graphs. 



