128 University of Calif or nia Publications in Geology [Vol.11 



County; the paratype, shown in his figures 5a and 5b, came from the 

 Turritella ocoyana beds from Barker's ranch near Bakersfield. This 

 latter form is very distinct from the specimens of Area montereyana 

 found in Contra Costa County. The writer's conclusions are based 

 upon the study of Osmont's original material, together with a large 

 number of specimens both from Contra Costa County and Barker's 

 ranch. The Barker's ranch specimens are different from those from 

 Contra Costa County in being shorter ; the posterior end is less 

 oblicpiely truncated. On the typical A. montereyana the surface in 

 front of the truncated margin and below the posterior dorsal margin 

 slopes up evenly to the main surface immediately below the beaks ; 

 on the specimens from Barker's ranch this area is rather strongly 

 depressed, giving this portion of the shell a subtabulate appearance 

 very similar to that seen on A. mediaimpressa. The beaks on the 

 form from the Barker 's ranch locality are more prominent ; also, on 

 most of the specimens from this locality there are two grooves border- 

 ing the medium groove on the lower parts of most of the ribs, similar 

 to that seen on A. trilineata Conrad; this character has not been 

 observed on any specimens of A. montereyana from Contra Costa 

 County. To this new species he gives the name Area barkeriana. 



Area mediaimpressa is somewhat similar to A. barkeriana in 

 outline and sculpturing ; it is narrower anteriorly ; the umbones 

 are broader and flatter, with the tendency to the medium impression 

 below the umbones, not seen on the other form; the largest specimen 

 known is much smaller than the average specimen from the Barker's 

 ranch locality ; the arrangement of the teeth on the hinge plate is 

 different, those on A. meelkiimpressa being set obliquely (converging 

 ventrally) to the hinge plate while on the other species they are almost 

 at right angles to it ; again, the medium grooving of the ribs on 

 A. mediaimpressa is only slightly shown on the larger specimens, while 

 on the other form it is well developed, many times with the second 

 and third grooves bordering it, as described above. 



ARC A (SCAPHARCA) SUBMONTEREYANA, n. sp. 

 Plate 16, figure 2 

 Type specimen 11186, Coll. Invert. Palae. Univ. Calif., loc. 52 

 Shell plump, medium in size, fairly heavy, rhombic in outline; beaks rather 

 prominent and anterior to the middle of the shell. Posterior end broadly rounded ; 

 anterior end regularly rounded, sloping down rather obliquely to the ventral edge. 

 Ventral edge gently convex. Surface of shell radially sculptured by about twenty- 

 three flat-topped ribs with interspaces averaging about the width of the tops of 

 the ribs ; on some specimens, there is a groove or channel down the middle of some 



