376 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL. XXXIV, 
Notes.—This gibbous little Leda is easily distinguished from asso- 
ciated fossil forms by its small size, great convexity, broad outline, 
sharply attenuate posterior extremity, excavated margin posterior to 
umbo, and rather coarse sculpture. It resembles Z. acuta Conrad 
(recent) in size but is relatively broader and more excavated behind. 
Distinguishable from the closely allied Z. taphria Dall by much 
smaller size, more excavated dorsal posterior margin, and finer con- 
centric sculpture. 
Named for Cahill Ridge, west of Redwood City, on the flanks of 
which is the type-locality. , 
Type-—h. 8. J. U., No. 1065. (Locality No. 57.) 
Horizon.—Vaqueros formation, Lower Miocene. 
Locality.—Santa Cruz quadrangle, San Mateo County, locality 
No. 57, on road to Kings Mountain House, 2 miles west of Woodside, 
in rather coarse, brownish-yellow sandstone. (W. A. Williams.) 
Genus YOLDIA Moller. 
YOLDIA SUBMONTEREYENSIS, new species. 
Plate XXXIV, fig. 8. 
Description.—Shell attaining a length of 82 mm., width about two- 
thirds of length, oblong, rounded in front, somewhat attenuated, 
angular, and slightly gaping behind, compressed; margin smooth; 
umbo central; anterior dorsal margin nearly straight, anterior ex- 
tremity broad and evenly rounded; posterior dorsal margin concave, 
curving upward at posterior extremity, but not prominently exca- 
vated immediately in rear of umbo; basal margin curving up sharply 
behind and meeting dorsal margin in a right angle, although the ex- 
treme end is slightly posterior to the angle; a faint carina, separated 
from dorsal margin by impressed line or lunule, extends from umbo— 
to posterior extremity; surface sculptured by numerous regular, nar- 
row, incremental lamelle, which are abruptly truncated on the edge 
toward the umbo, slope off gently on the side toward the periphery, 
and become narrower posteriorly. 
CTS: coe ets 32 mm.; latitude, 21 mm.; diameter of single 
valve, 2.5 mm.; umbo to anterior extremity, 17 mm. (53 per cent 
of onvafitinidls). 
Notes.—This species is characterized by its size, the central posi- 
tion of the umbones, rather broad, slightly rounded, gaping posterior 
extremity and regular concentric lamelle. It is closely allied to Leda 
whitmant Dall (possibly a Yoldia) from the Miocene of Oregon, but 
differs from it in being less attenuate posteriorly and broader in out- 
line; the excavation behind the umbo in the latter is also more pro- 
nounced than in ¥. swhmontereyensis. It is smaller and less attenu- 
ated posteriorly than Y. oregona Shumard; is much smaller and 
