no. 1617. NEW CRETACEOUS AND TERTIARY FOSSILS—ARNOLD. 3175 
erenulated revolving rib adjacent to umbilicus, 1 or 2 incised grooves 
outside of this and finally 2 or 3 revolving raised lines toward the 
periphery; whole surface of whorls ornamented by numerous sharp, 
subequal, incremental lines which slope obliquely downward and 
backward from the upper margin. Umbilicus wide, spiral, and mar- 
gins crenulated by rib previously mentioned; aperture subquadrate ; 
hp simple. 
~ Dimensions.—Of type, imperfect specimen, approximate, altitude, 
8 mm.; latitude, 19 mm. | 
Notes—This beautiful species, of which a rather imperfect mold 
is the type, has so far been found only at locality No. 107. All of 
the specimens figured are wax casts from molds in the soft sandstone 
matrix. A. lorenzoensis is allied to A. hornii Gabb from the Tejon 
(Eocene), from which it differs by its larger size and spirally sculp- 
tured upper surfaces of the whorls, and also to A. blanda Dall from 
the Eocene of Fall Creek, Oregon, from which it differs by having 
raised spiral lines near the periphery, rather than an entire spiral 
sculpture of impressed grooves. 
Named for the San Lorenzo formation, of which it is believed to 
be characteristic. 
Type.—Imperfect mold, Cat. No. 165448, U.S.N.M. 
Horizon.—San Lorenzo formation, Oligocene. 
Locality.—Santa Cruz quadrangle, Santa Cruz County, locality 
No. 107, on small ravine off Boulder Creek, 2+ miles north of Eagle 
Rock. (RK. Arnold, I. Anderson. ) 
VAQUEROS (LOWER MIOCENE) SPECIES. 
JP je GSP OIA. 
Genus LEDA Sehumacher. 
LEDA CAHILLENSIS, new species. 
Plate XXXIV, fig. 9. 
Description.—Shell attaining a length of only 6 or 7 mm., width 
about seven-ninths of length, oval, rounded in front, attenuate be- 
hind; well inflated, margin smooth; umbo small, subcentral, turned 
backward; anterior dorsal margin nearly straight, sloping steeply 
from umbo; anterior extremity regularly rounded; posterior dorsal 
margin concave, prominently excavated behind umbo; posterior ex- 
tremity very attenuate; surface sculptured by numerous, equal, 
rounded concentric ribs, separated by moderately wide impressed 
lines; a trace of a poorly developed carina extending from the umbo 
to the posterior extremity is discernible in the type. 
Dimensions —Length, 6.5 mim.; latitude, 4.8 mm.; diameter of 
single valve, 1.9 mm. 
