1915] 



Clark: Fauna of the San Pablo Group 



491 



whorl there are seven of these spiral ribs, the interspaces between 

 which are unequal. Beginning at the suture, the first two interspaces 

 between the spiral ribbing' are about as wide as the tops of the ribs, 

 the next two interspaces are narrower than the tops of the ribs, the 

 next interspace is of the wide type and the one anterior to it is of 

 the narrow type. This gives the distribution of the ribs on the body 

 whorl as follows : Commencing at the suture, there are two spiral 

 ribs separated by a wide interspace ; these may be considered as a 

 pair; the posterior of the two is not as heavy as the other. Anterior 

 to this first pair is a group of three spiral ribs, separated by narrow 

 interspaces, and last a pair of less nodose spiral ribs, separated from 

 the group of three by a wide interspace, and from each other by the 

 narrower type of interspace. This last pair of ribs is situated on the 

 angle between the side of the body whorl and the base, the anterior 

 rib being partly on the base. 



The spiral ribbing on the whorls of the spire is the same as on 

 the body whorl, except that the anterior pair of ribs is lacking; thus 

 beginning at the lower suture there is a group of three spiral ribs 

 separated by narrow interspaces ; posterior to this is the pair sep- 

 arated by wider interspaces, the rib next to the suture not being as 

 heavy as the other. 



Base of body whorl smooth, nearly flat. Peristome subquadrate ; 

 columella with one distinct plication. (There were probably at least 

 two plications). The anterior end of the columella of the type is 

 broken. Inner lip not incrusted. 



Dimensions. — Height, about 8 mm. 



Occurrence. — Upper San Pablo of Las Trampas Ridge, University 

 of California locality 1182. 



CERITHIUM EODEOENSIS, n. sp. 

 Plate 69, figures 1 and 10 

 Shell medium in size, turreted ; apex acute ; number of whorls 

 eight or nine. Sides of whorls convex. Sutures depressed. Surface 

 of whorls sculptured by narrow, prominent spiral ribbing with inter- 

 spaces usually wider than the tops of the ribs ; whorls of spire with 

 five to six of these revolving ribs ; on the body whorl there are about 

 fifteen of the revolving ribs, which are coarser posteriorly near the 

 suture while anteriorly on the base they become finer and closer 

 together. "Whorls also sculptured by thirteen or fourteen variable 



