24 PALEONTOLOGY OP CALIFORNIA. 



diameter. The figures of the shells illustrate the most marked 

 forms of this somewhat variable species. 



Named after Prof. J. D. Whitney, State Geologist of California. 



AMMONITES, Brug. 



A. Blakei, n. s. 



PI. 4, Pigs. 14, 15. 



Shell discoidal, compressed. "Whorls five or six, truncated 

 somewhat abruptly on the umbilical margin, usually flattened on 

 the sides, rounded towards the dorsum, which is sometimes cari- 

 uate, sometimes rounded. Body whorl enveloping about three- 

 fourths of the preceding one. Umbilicus deep. Surface some- 

 times plain, or merely undulated; at other times, it is marked 

 by numerous ribs, which cross the sides, arching forwards from 

 the margin of the umbilicus to near the dorsum, where they 

 generally become obsolete. These ribs sometimes commence 

 with a strongly marked tubercle, although they are usually plain. 

 There are also usually supplementary ribs at irregular intervals. 

 These ribs arise in the middle or towards the ventral side of the 

 whorl; and, at a short distance from their origin, become as large 

 as the primary ribs. 



Septum : Dorsal lobe divided, at the extremity, into two short 

 branches, each ending in three teeth ; above these branches are 

 two notches on the side of the lobe ; dorsal saddle about as wide 

 as the lobe, and marked by three shallow notches ; superior lateral 

 lobe' a third larger than the dorsal, bifurcate at the end and 

 toothed at the sides ; lateral saddle like the dorsal; inferior lateral 

 lobe smaller than the dorsal, with two processes at the end and 

 one on each side. Besides these there are two supplementary lobes 

 and saddles much smaller than those described. Diameter, 1.85 

 inch. Width of body whorl, .85 inch. "Width of mouth, .55 inch. 



A specimen was collected by Mr. It. Homfray, near Star City, Humboldt, six 

 inches in diameter, and with a row of large nodes on the middle of the whorl, 

 from which the ribs bifurcated. 



