1915] 



Clark: Fauna of the San Pablo Group 



501 



MUEEX (OCINEBRA) DALLI, n. sp. 

 Plate 67, figures 4 and 9 

 Shell medium in size, fusiform, fairly heavy; apex acute. Whorls 

 regularly convex ; number of whorls seven ; spire a little over one- 

 half the height of the body whorl. Shell sculptured by medium coarse, 

 rounded, revolving ribs, the interspaces between which are much nar- 

 rower than the tops of the ribs ; on the body whorl there are about 

 twenty-two of these revolving ribs, on the whorls of the spire there 

 are five or six. On some specimens, available for study, every other 

 spiral rib stands out more prominently, thus showing an alternation 

 of a rib and an interrib. This is true of the specimens from locality 

 1182 to the south of Walnut Creek, Contra Costa County. Surface 

 of shell also sculptured by eight or nine prominent, rounded, longi- 

 tudinal ribs ; these longitudinal ribs show considerable variation in 

 prominency and tend to be split or grooved. Mouth ovate ; outer lip 

 sometimes thickened externally, dentate internally; inner lip heavily 

 encrusted; canal medium in length, straight and deep; on some speci- 

 mens it is entirely closed, on others only partially; columella subper- 

 forate. 



M. dalli differs from M. selbyensis, n. sp., a species found in the 

 Lower San Pablo, in that it is a more slender shell; the spire is higher, 

 and the canal longer, and the spiral ribbing does not become obsolete 

 next to the suture. 



Named in honor of Dr. W. H. Dall of the Smithsonian Institute. 



Dimensions. — Type specimen : height, 23 mm. ; height of body 

 whorl, 4 mm. ; greatest width of body whorl, 12 mm. 



Occurrence. — This form so far has been found only in the Upper 

 San Pablo. It is found associated with Astrodapsis tumidus Remond. 

 Tivela gabbi, n. sp., Trophon carisaensis Anderson, etc. University of 

 California localities 1620, 1881, 521, etc. 



MUEEX (OCINEBRA) PACKARDI, n. sp. 

 Plate 69, figures 2 and 11 

 Shell elongate-oval, heavy, rather large for this genus. Spire 

 high ; apex acute ; sutures deeply depressed. Whorls strongly and 

 regularly convex ; body whorl a little less than two-thirds the height 

 of the spire. Surface covered by rather coarse, broadly rounded, re- 

 volving ribs with interspaces slightly wider than the ribs ; in each 

 interspace there is a narrow, low riblet ; on each of the first two whorls 



