f8 PALEONTOLOGY OF CALIFORNIA. 



Figures, half natural size. 



Locality : Found in Div. A, of the Cretaceous, abundantly on the north fork of 

 Cottonwood Creek ; also at Arbuckle's Diggings, Shasta County; and a specimen 

 was picked up by Mr. Esmond on the shore of the Straits of Carquines, west of 

 Martinez. 



In the square dorsum and the mode of costation, this shell is not unlike some 

 of the forms of Ammonites Remondii (supra); but it can be at once distinguished 

 by the separation of the whorls. 



ANCYLOCERAS, D'Orb. 



A. (sp. indet.) 



PI. 15, Fig. 30, and 30 a. 



FOUR specimens of this fossil have been discovered, two at 

 Cottonwood Creek, and two at Arbuckle's Diggings, Shasta 

 County. They all agree in being nearly cylindrical, the section 

 being elliptical. They taper very gradually from one end to the 

 other, and are all of nearly the same size. They differ, however, 

 somewhat in the surface-markings, the ribs being more or less 

 distinct, and in the angle which these ribs take with the axis of 

 the shell. In one specimen, the ribs are well marked, curved, 

 and occasionally dichotomous; in another they are much more 

 oblique, more numerous, and vary very much in size. 



The septum is composed of a dorsal and ventral lobes, and two 

 lateral ones on each side. Dorsal lobe divided for half its length, 

 each branch bearing four or five external lateral spurs, and three 

 or four smaller internal ones; between these branches are two 

 small, distant, tongue-like spurs; above the origin of the termi 

 nal branches are two large lateral ones, the upper one being the 

 smaller. Dorsal saddle broad, deeply divided into two lobes, 

 each of which is divided into two smaller ones, which are in turn 

 subdivided. Superior lateral lobe placed in the middle of the 

 septum; longer than the dorsal lobe, with the body more slender; 

 divided at the middle into three very large branches, the middle 

 one nearly straight, and almost an exact miniature of the whole 



