Clark: The San Lorenzo Series of Middle California 149 



Genus CHIONE Megarle von Muhlfeld 

 CHIONE CEYPTOLINEATA, n. sp. 

 Plate 5, figures 1, 2, 3 and 4 

 Type specimen 11178, Coll. Invert. Palae. Univ. Calif., loe. 1131 



Shell heavy, longer than high, subovate in outline; beaks prominent, strongly 

 mturned. Anterior slope short ; posterior slope long, gently convex for a short 

 distance below the beaks, beyond which it is straight. Anterior end rather 

 strongly produced, regularly rounded; posterior end regularly rounded. Lunulc 

 large, rather strongly depressed, cordate, pouting, concentrically sculptured by 

 rather fine, sharp, closely crowded lamellae. Escutcheon well defined, depressed 

 a little more than at right angles to the main outer surface of the shell, being 

 more distinct and covered by finer incremental lines on the left valve than on 

 the right. Main surface of shell covered by prominent and fairly equally spaeed 

 sharp lamellae which, on the unweathered specimens, are almost two millimeters 

 high. Surface on weathered specimens radially sculptured; these radial ribs 

 are fine and close together and apparently do not extend onto the lunule or 

 escutcheon; margins internally crenulate ; the radials are internal and do not 

 show on unweathered specimens. Three cardinals on each valve ; on the right 

 valve the two posterior cardinals are strongly bifid; on the left valve the posterior 

 cardinal is long and narrow and situated on top of the nymph plate, the middle 

 cardinal is bifid and the anterior cardinal is higher than the other two. The 

 posterior dorsal edge of the right valve is grooved to receive the corresponding 

 edge of the opposite valve. Pallial sinus short and bluntly rounded. 



Dimensions. — Type specimen : greatest dorsal-ventral height, 49 mm. ; greatest 

 anteroposterior length, 59 mm. ; length of posterior dorsal slope, about 47 mm. : 

 length of anterior dorsal slope, about 16 mm. ; greatest diameter of both valves, 

 19 mm. 



Occurrence. — University of California localities 1131, 1686, 14, 1343, etc. 



This species is quite distinct from, but in some cases, with poor 

 material, might be mistaken for C. mediostriata, which is found in 

 the same horizon. In outline it differs from the latter species in being- 

 longer in proportion to the height ; the anterior end is more regularly 

 rounded; the lunule is different in that it is pouting and is not so 

 wide ; the escutcheonal area is not quite so strongly depressed. The 

 greatest difference between the two species is that on C. mediostriata 

 there are four cardinal teeth in the right valve, while on C. crypto- 

 lin&ata there are only three. On the right valve of C. cryptolineata 

 the anterior cardinal is not so high and is longer than the correspond- 

 ing tooth on C. mediostriata. The posterior cardinal of the left valve 

 of C. cryptolineata is situated on top of the nymph plate, while the 

 same tooth on C. mediostriata is separated from the nymph plate by 

 a distinct groove, into which fits the fourth posterior cardinal of the 

 right valve. 



