74 PALAEONTOLOGY OF CALIFORNIA. 



PTYCHOCERAS, D'Orb. 



P. JEQUICOSTATUS, 11. S. 

 PI. 13, Fig. 20. 



Shell robust, section subcircular, slightly flattened on tbe ven- 

 tral side. Surface ornamented by a series of rounded ribs with 

 regularly concave interspaces. These ribs appear to differ in size 

 only in proportion to the growth of the shell ; they pass entirely 

 around the shell, obliquely backwards from the ventral to the 

 dorsal side, being somewhat faint on the ventral surface. There 

 is no sign of bifurcation of these ribs on any of the specimens I 

 have seen. From one imperfect impression, showing twenty-six 

 ribs, it seems that on a single rib there have been two tubercles 

 or spines ; one near the dorsal and the other near the ventral 

 side. This is on the small branch. I can detect no trace of this 

 character on any of the other specimens. 



Figure, natural size. 



Localities: North fork of Cottonwood Creek, Alderson's Gulch, and Eagle Creek, 

 Shasta County (Div. A.). 



P. (? Hamites) QUADRATUS, 11. S. 

 PI. 15, Fig. 21 ; PI. 14, Fig. 21 a. 



Shell small, section subquadrate, angles rounded, sides nearly 

 flat, dorso-ventral diameter about a third more than the trans- 

 verse. Surface marked by very small rounded ribs, which cross 

 at right angles with the length, and become linear and slightly 

 arched forwards on the ventral side. Besides these ribs are pe- 

 riodical constrictions, placed about the width of the shell apart, 

 and which arc deepest on the sides and back. 



Septum : Dorsal lobe slender, divided into two bifurcate 

 branches, and with three regularly diminishing spurs above. 

 Saddles all of the same pattern, but differing in size. Dorsal 

 wider than the lobe, deeply bifurcate, each branch divided into 



