150 University of California Publications in Geology [Vol. n 



CHIONE LINEOLATA, n. sp. 

 Plate 6, figures 1, 2 and 5 



Type specimen 11123, Coll. Invert. Palae. Univ. Calif., loc. 1131 

 Shell heavy, medium in size, subtrigonal in outline, longer than high ; beaks 

 prominent. Anterior slope short, gently concave ; posterior slope long, gently 

 convex. Anterior end evenly rounded ; posterior end subangulate ; ventral edge 

 gently arcuate. Lunule large, cordate, concentrically sculptured only. Dorsal 

 edge of lunule in right valve slightly convex just below the beaks. Escutcheon 

 well-defined, depressed more than at right angles to the main outer surface of 

 shell ; area more distinct and less coarsely sculptured on left valve than on right ; 

 margins internally erenulate. Surface of shell covered by heavy, coarse concentric 

 ridges or lamellae which, near the beaks, are rather wide apart but become closely 

 crowded near the ventral edge ; surface also sculptured by medium fine, closely 

 crowded, radial ribs which become obsolete on the posterior dorsal margin, and 

 which are probably internal, not showing on unweathered specimens. Hinge 

 plate heavy ; ligamental groove deep. Three strong, equally spaced cardinals in 

 right valve, none of which are bifid. On the left valve the posterior cardinal is 

 elongate, fairly prominent and situated on top of nymph plate ; the middle 

 cardinal is deeply bifid ; anterior cardinal higher than the other two, bluntly 

 pointed. Posterior dorsal edge of right valve below ligamental groove channeled 

 to receive the corresponding edge of the opposite valve. 



Dimensions. — Type specimen : greatest dorsal-ventral height, 55 mm. ; greatest 

 anteroposterior length, 62 mm.; length of posterior dorsal slope, 53 mm.; length 

 of anterior dorsal slope, about 19 mm. ; greatest diameter of one valve, 21 mm. 



Occurrence. — University of California locality 1131, about three-fourths of 

 a mile southwest of the town of Walnut Creek. 



For a comparison of this species with C. mediostriata see the de- 

 scription of the latter species. 



C. lincolata rather closely resembles C. securis Shumard, 121 a 

 species very common in the Upper Miocene of Oregon and Washing- 

 ton. The anterior end of C. lineolata is more strongly produced than 

 on C. securis, the ventral edge is not so arcuate, the escutcheonal area 

 is more depressed and sharply defined, and the lunule is somewhat 

 larger. The hinge plate of the right valve of C. securis, as figured 

 by Dall, is quite different from that of C. lineolata. 



CHIONE MEDIOSTEIATA, n. sp. 

 Plate 5, figures 5 and 6; plate 6, figures 3 and 4 

 Type specimen 11181, Coll. Invert. Palae. Univ. Calif., loc. 1131 

 Shell heavy, medium in size, cordate ; beaks prominent, strongly inturned and 

 prosogyrous. Anterior slope short and slightly concave; posterior slope long 

 and gently convex. Posterior end subangulate to bluntly rounded; anterior end 



i2i See description and figure of C. securis given by Dall, U. S. Geol. Surv., 

 Prof, paper 59, p. 120, pi. 11, fig. 8; pi. 13, figs. 2, 9, 1909. 



