no. 1617. NEW CRETACEOUS AND TERTIARY FOSSILS—ARNOLD. 365 
confluence with San Lorenzo River; locality No. 107, in small ravine 
off Boulder Creek, 2+ miles north of Eagle Rock; localities Nos. 115, 
‘116 and 117, the first two on the headwaters of the South Fork, the 
last on the headwaters of the North Fork, of Waddell Creek, in the 
Big Basin. (R. Arnold, W. R. Hamilton, H. L. Hamilton, etc.) 
Genus MALLETIA Desmoulins. 
MALLETIA CHEHALISENSIS, new species. 
Plate XX XIII, figs. 9, 9a. 
Description.—Shell attaining a length of 25 mm., oval, compressed, 
smooth; umbones rather inconspicuous, slightly anterior to middle, 
turned backward; -anterior dorsal margin sloping straight from 
umbo; anterior extremity regularly rounded; posterior dorsal margin 
straight, depressed immediately in rear of umbones; posterior ex- 
tremity above medial line, more attenuated than the anterior; pos- 
terior portion of base near extremity nearly straight, otherwise 
quite regularly curved. Surface smooth, except for faint concentric 
lines. Hinge consists of a row of sharp teeth flexed toward the umbo 
on each side of a prominent, projecting umbonal pit. Pallial sinus 
large and deep. | 
Dimensions —Length, 7.4 mm.; latitude, 4.5 mm.; diameter of sin- 
gle valve, 1.5 mm. 
Notes—This species is very closely allied to d/. gibbsit Dall, 
dredged at U.S. Bureau of Fisheries Station 2860 in 876 fathoms off 
(Queen Charlotte Island, but may be distinguished from the latter 
by its prominent umbonal pit and straighter posterior dorsal margin. 
The type is a rather undersized specimen, chosen for its perfect state 
of preservation, the species usually attaiing a larger size. The 
specimens from the Santa Cruz quadrangle reach a length of over 
12 mm. 
Named for Chehalis County, Washington, where the type was 
found. | : 
Type.—Cat. No. 165447, U.S.N.M., Porter, Chehalis County, 
Washington. 
Horizon.—San Lorenzo formation, Oligocene (Santa Cruz re- 
gion; Oligocene (Porter, Washington) ; base of Oligocene-Miocene 
(Washington). 
Localities—Santa Cruz quadrangle, Santa Cruz County, locality 
No, 103, Kings Creek, three-eighths mile above its confluence with 
San Lorenzo River; locality No. 104, on Boulder Creek, 5 miles north- 
west of its confluence with the San Lorenzo River; locality No. 106, 
on Twobar Creek, 1 mile above its confluence with the San Lorenzo 
River; locality No. 107, small ravine off Boulder Creek, 24 miles 
horth of Eagle Rock (R. Arnold) ; also in basal portion of Oligocene- 
