MIOCENE PECTENS. 69 



Pecten (Chlamts) sespeexsis n. sp. 



PI. VIII. fifrs. :.', -2(1, and :!. 



1888. Pecten hmtliitusfCoo-per (not 8owerby), Seventh Ann. Kept. Cal. St. Min., IS.SS, p. i57 (Miocene 

 o£ Estrella, San Luis Obispn County?). 



Description. — Shell averaging about 50 millimeters in altitude, higher than long, 

 inequivalve but both valves equally slightly convex, rather thin, and et|uilateral, 

 except for ears. Right valve with about 9 pairs of narrow, rounded, nearlj' smooth 

 ribs, each pair being separated from the adjacent ones b}^ interspaces, which are gen- 

 erally slightly wider than the interspace between the members of the pair; surface 

 sculptured by incremental lines; hinge line about two-thirds length of disk; anterior 

 ear much produced, sculptured by several prominent radials and numerous incre- 

 mental lines; posterior ear over one-half as long as anterior, and sculptured similarly; 

 bj'ssal notch prominent. Left valve with about nine prominent, narrow, sciuarish, 

 somewhat convex-topped ribs separated })v much broader interspaces, along the 

 })ottom of which run one or more thread-like intercalaries of greater or less prom- 

 inence; ears similar to those of the right valve. 



Dimensions. — Alt. 37 mm.; long. 3<) mm.; hinge line 19 mm.; diameter 12 mm.; 

 umbonal angle 75°. 



This species is closely allied to, and is probably the precursor of P. hastatus 

 Sowerby. It corresponds to P. Jidstatus in size, shape, and number of major ribs, 

 but diflers from the latter in having longer anterior ears and scarcely any secondary 

 sculpture of minor riblets and scaly surface. P. sespeensis approaches more closely 

 to the smooth form of /'. hastatus found in the Pliocene, but may be easily dis- 

 tinguished from that form by its longer posterior ears and lack of much secondary 

 sculpture. 



The only specimens of this species known are rather poorly preserved casts, 

 with now and then small fragments of the shell hanging to them, which come from 

 beds of lower Miocene age, locallj' known as "oil rocks." in the Sespe oil district, 

 Ventura Count}'. Type and cotype. No. 12480, California State Mining Bureau. 

 Other specimens of the same species, Nos. 12i27 and 14759 C. S. M. B. On Tar 

 Creek, Ventura County, Mr. Eldridge found P. sespeensis associated with Turritella 

 (cf.) hoffmaiini, Ostrea sp., and Modiolus sp. 



Miocene (lower.) Sespe oil district, Ventura County (Watts); Tar Creek, Ventura 

 County (Eldridge). 



Pecten (Chlamys) sespeensis var. hydei n. var. 



PI. V, figs. 8, Sd, and 'Ah. 



1903. Pecten {Chlamys) hydei .\rnold. MS. 



Description. — Shell' averaging about 45 millimeters in altitude, much higher 

 than long, subequivalve, slightly convex, and subequilateral, except for ears; 

 anterior sides more concave than posterior; base regularly rounded; umbonal angle 



