364 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL. XXXIV. 
Type.—External mold of almost perfect spine, L.S8.J.U., No. 1056. 
(Locality, No. 109.) 
Horizon.—San Lorenzo formation, Oligocene, upper portion transi- 
tional toward Vaqueros formation, lone Miocene. 
Locality.—Santa Cruz quedeanele: Santa Cruz County, Tecate 
No. 109, on Bear Creek, 4 miles above its confluence with the San 
Lorenzo River. (J. F. Newsom.) 
PELECYPODA. 
Genus NUCULA Lamarek. 
Subgenus ACILA H. and A. Adams. 
NUCULA (ACILA) DALLI, new species. 
Plate XX XIII, fig. 15. 
Description.—Shell trigonal in outline, nearly as broad as long, 
large for a member of this genus, sometimes attaining a length of over 
30 mm., rather compressed, strongly divaricately sculptured. Umbones 
prominent and turned backward, placed very near the posterior 
end, which is abruptly truncated and depressed, and forms a straight 
or shehtly inwardly curved line from the umbones to the base, with 
which it makes a sharp angle of about 90°; base rounded, becoming 
more and more so toward the anterior extent. which region ex- 
hibits the sharpest curvature of any on the anterior portion of the 
shell; anterior dorsal margin nearly straight for a considerable dis- 
tance in front of the umbones; a faint carina extends from the umbo 
to the posterior ventral angle; surface sculptured by numerous 
rounded, raised, divaricating lines; margins crenulate. Hinge as in 
other members of this genus. 
Dimensions.—Length, 33 mm.; latitude, 28 mm.; diameter of both 
valves together about 14 mm. 
Notes.—This magnificent species is easily distinguishable from the 
other west coast forms by its great size, great breadth, and coarse, 
well defined sculpture. In size it approaches the gigantic Acida mira- 
bilis Adams and Reeve, from the recent fauna of Japan. 
Named in honor of Dr. William Healey Dall, of the United States 
Geological Survey. 
Type.—Mold of exterior of left valve, Cat. No. 165452, U.S. NM. 
(Locality No. 115.) 
Horizon—San Lorenzo formation, Oligocene, and possibly also 
the Monterey shale, middle Miocene. : 
Localities —Santa Cruz quadrangle, Santa Cruz County, locality 
Nos. 100, 101, and 102, on San Lorenzo River, 3, 34, and 54 miles, 
respectively, above the town of Boulder Creek; locality No. 103, 
Kings Creek, three-eighths mile above its confluence with San 
Lorenzo River; locality No. 104, Boulder Creek, 5! miles above its 
