76 PALEONTOLOGY OF CALIFORNIA. 



Figure, natural size. There are specimens which show about a third of a volu- 

 tion in addition to the size figured. 



C. LATUS, 11. S. 

 PI. 15, Fig. 25, and 25 a; and PI. 14, Fig. 25 6. 



Shell broadly spiral; section of whorls nearly as broad as high, 

 narrowest towards the dorsum. Surface ornamented by alternate 

 large and small ribs ; of the former, there are twenty-six or 

 twenty-seven on the last whorl, with sometimes three, sometimes 

 four of the small ones between each pair. These ribs commence 

 on the ventral margin and cross towards the back, either directly 

 or curving slightly backwards, and then bend slightly forwards 

 in crossing the dorsum. The ventral surface is marked by very 

 small ribs, which arch strongly forwards. Each large rib bears 

 on its dorsal front two spines, which are represented by tubercles 

 on the cast. Besides these, there are two others on each side, 

 one on the ventral margin, and one about midway between this 

 and the one on the dorsum. 



Septum composed of a dorsal and ventral lobes, and two lateral 

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

 with a small bilobate tongue in the middle ; each branch carries 

 two lateral projections; above the origin of these branches are 

 two smaller spurs, the upper one smallest. Dorsal saddle bilo- 

 bate ; each branch divided into three or four smaller ones. Supe- 

 rior lateral lobe longer than the dorsal, divided at the middle into 

 three enormous branches, the middle one of which is straight, 

 trifurcate at the end, and with two small spurs above on each 

 side; lateral branches long, curving downwards; that on the 

 dorsal side longest, and both with several side spurs. Above 

 the origin of these branches the lobe has on each side a couple 

 of spurs, the longest being below. Lateral saddle of the same 

 pattern as the dorsal, but smaller. Inferior lateral lobe not more 

 than half as long as the superior lateral, more simple, but of the 

 same pattern. Ventral saddle half the size of the dorsal, divided 

 in nearly the same manner. Ventral lobe as long, nearly as 



