Geol.— Vol. I.J SMITH— LYTOCER AS AND PHYLLOCERAS. 1 47 



Phylloceras onoense Stanton. 



Plates XIX and XX. 



Phylloceras ramosum Gabb, Pal. Cal., Vol. I, p. 65, PI. XI, fig. 12; PI. XII, 



fig. 12. 

 Phylloceras onoense Stanton, Bull. 133, U. S. Geol. Survey, p. 74. 

 (Not P. ramosum Meek, Bull. Geol. and Geog. Survey Terr., Vol. II, No. 



4, P- 37I-) 



This species from the Horsetown beds of the Lower Cre- 

 taceous was identified by Gabb with Meek's species from 

 the Upper Cretaceous of Puget Sound. But Dr. Stanton 

 has recently broken this up into three species in a genetic 

 series, P. knoxvillense Stanton, from the Knoxville beds, 

 Lower Cretaceous; P. onoense Stanton, Horsetown beds, 

 Gault; and the real P. ramosum Meek, from the Upper 

 Cretaceous. Stanton says that P. onoense differs from 

 P. knoxvillense in lacking constrictions, but these were 

 observed on several specimens from Cottonwood creek, 

 Shasta county, and from Alameda county. 



Ontogeny. 



Larval stages. — No protoconch was separated from the 

 later chambers, but its shape can easily be seen on PI. XIX, 

 fig. I, and PI. XX, fig. i. It is very like that of Lytoceras 

 alamedense . The ananepionic stage, shown by the nauti- 

 loid septum (PL XX, fig. i), shows a broader and longer 

 abdominal saddle than Lytoceras, but is otherwise like it; 

 the pear-shaped siphonal caecum or knob could be seen 

 clearly inside of the protoconch. The metanepionic stage 

 lasts only through the second septum (PL XX, fig. i); it 

 has an undivided, rounded, ventral lobe, and two external 

 lateral lobes, and probably corresponds to the stock Prole- 

 canitidse, from which Phylloceras came. 



With the third septum comes the divided ventral lobe of 

 the paranepionic stage (PL XX, fig. i); this agrees with 

 the Nannites stage of Lytoceras, and probably shows the 

 connection with that genus. This stage lasts up to diameter 

 of 1. 15 mm., one and five-twelfths coils, is smooth except 

 for a constriction at end of the first coil. Its lobes are 



