436 SMITHSONIAN MISCELLANEOUS COLLECTIONS [vol. 50 



spaced, narrow concentric riblets, this sculpture confined to the main 

 portion of shell ; lunule, escutcheon, and carinas ornamented only by 

 fine concentric incremental lines; incremental lines also visible be- 

 tween the concentric riblets. Hinge and interior similar in a general 

 way to L. minuta Fabr. 



Dimensions. — Longitude, 7 mm. ; altitude, 4.2 mm. ; diameter, 

 3 mm. 



Notes. — This beautiful little Leda is allied to L. minuta Fabr., but 

 differs from it in being less attenuate posteriorly, having coarser and 

 wider spaced concentric riblets, and in having simple rather than 

 biangular carinas. A rather abundant species in the finer fossiliferous 

 sands and shales of the lower Pliocene. Named in honor of Mr. 

 W. W. Orcutt, of Los Angeles, California. 



Type.— Cat. No. 165,271, U. S. N. M. 



Locality. — Waldorf asphalt mine, 3 miles southeast of Guada- 

 lupe, Santa Barbara County, California; locality No. 4473. 



Horizon. — Fernando formation, lower Pliocene portion. 



PHACOIDES NUTTALLII Conrad, var. ANTECEDENS, new variety 



PI. LV, fig. 6 



Description. — Shell averaging about 25 millimeters in longitude, 

 very broadly elliptical in outline, longer than high, ventricose, and 

 equivalve ; beaks only moderately prominent, placed slightly anterior 

 to middle of shell ; base arcuate ; anterior margin sloping more 

 rapidly from beaks than posterior, the latter being nearly straight 

 for about 6 or 8 millimeters from the beaks ; both extremities quite 

 regularly rounded, the posterior being possibly slightly more atten- 

 uate, sculpture consisting of numerous close-set subequal rounded 

 radiating ridges and concentric ribs which are narrower than the 

 radials, and spaced about twice the distance between two of the 

 latter; the concentric ribs tend to become obsolete toward the 

 periphery in adult specimens ; the general appearance of the surface 

 is decidedly cancellate. Lunule deep, small, and inconspicuous. 

 Interior and hinge as in P. nuttallii. 



Dimensions. — Longitude, 23 mm. ; altitude, 19 mm. ; diameter, 

 12 mm. 



Notes. — This variety is more ventricose, less angulated pos- 

 teriorly, and has its concentric ribs much wider spaced than the 

 typical P. nuttallii. 



Type.— Cat. No. 165,290, U. S. N. M. 



