496 University of California Publications in Geology [Vol. 8 



the ribs. Besides the revolving' ribbing' there is a finer longitudinal 

 series of ribs, the width of the interspaces of which is about equal to 

 the interspaces of the revolving ribs, thus marking off the surface into 

 little squares ; this longitudinal ribbing becomes obsolete on the anterior 

 end of the body whorl. Mouth elongate-ovate ; outer lip sharp ; inner 

 lip smooth ; canal short and straight. 



Dimensions. — Height, about 27 mm.; maximum width of body 

 whorl, 13 mm. ; height of body whorl, 16 mm. 



Occurrence. — In the Upper San Pablo Group to the southeast of 

 Walnut Creek, Contra Costa County, Calif., University of California 

 locality 1263. 



CHBYSODOMUS PABLOENSIS, n. sp. 

 Plate 67, figure 8 



Shell heavy, rather large ; whorls strongly and regularly convex. 

 Body whorl nearly two-thirds the height of the shell. Whorls five or 

 six. Sutures appressed. Surface sculptured by heavy, flat-topped 

 spiral ribs, alternating irregularly with a narrower and finer spiral 

 ribbing ; interspaces between the major spiral ribs are usually about 

 as wide as the tops of the larger ribs. On the body whorl there are 

 usually eleven or twelve of the major revolving ribs, and an equal 

 number of the interribs ; anteriorly on the body whorl of the larger 

 specimens the interribs become almost if not entirely as prominent as 

 the major ribs. On the whorls of the spire there are eight fairly heavy 

 spiral ribs ; in the interspaces of some of these there is an interrib. 

 Posteriorly the sutural rib on each whorl is heavier and more promi- 

 nent than the others, partially concealing the suture and giving a 

 collar-like effect to the whorl. Outer lip sharp ; inner lip smooth ; 

 umbilicus subperforate ; canal short. 



C. pabloensis appears to be closely allied to C. portalensis Arnold, 

 the main differences being that on the former the spiral ribbing ap- 

 pears to be somewhat heavier and it lacks the longitudinal ribs seen 

 on the whorls of the spire of the latter ; otherwise the two species are 

 remarkably similar. 



Chrysoclomxis pabloensis is somewhat similar in sculpturing to C. 

 cierboensis, n. sp.. which is also found in the Lower San Pablo Group ; 

 it differs in being more ventricose ; the canal is not so long, and it has 

 the collar-like rib next to the suture not seen on C. cierboensis. 



Dimensions. — Type specimen : height, about 65 mm. ; greatest width 

 of body whorl, 38 mm. 



