no. 1617. NEW CRETACEOUS AND TERTIARY FOSSILS—ARNOLD. 3879 
from the latter in being bilaterally more symmetrical on account of 
being less produced in the ventro-posterior region, having only about 
three-fourths as many ribs (34 instead of about 45), having narrower, 
steeper sided ribs and a more prominent angle extending from umbo 
to posterior extremity. It differs from (. guadrigenarium Conrad, 
var. fernandoensis Arnold, from the lower Pliocene, by being much 
larger, more convex, having more prominent umbones, and having 
fewer, wider, deeper, steeper-sided imterspaces. Named for the 
Vaqueros formation, of which it is believed to be characteristic. 
Type.—Imperfect right valve, Cat. No. 165457, U.S.N.M. (Local- 
ity No. 12.) 
Horizon.—Vaqueros formation, lower Miocene. 
Localities —Santa Cruz quadrangle, San Mateo County, locality 
No. 12, Mindego Creek, 1 mile above its confluence with Alpine 
Creek. (R. Arnold, H. H. Holly, L. C. Mulls.) 
GASTEROPODA. 
Genus AGASOMA Gabb. 
AGASOMA SANTACRUZANA, new species. 
Plate XXXIV, fig. 7. 
Description.—Shell attaining a length of at least 40 mm., pyriform ; 
spire short and small compared with body whorl, consisting of 4 to 5 
whorls; upper whorls convex, minutely cancellated by about 4 spiral 
and numerous less prominent axial, sharp, raised lines; body whorl 
surmounted by a prominent outwardly expanding carina carrying 14 
or 15 unequal, irregularly placed, rounded, raised tubercles; between 
the carina and the suture there is an irregular cord-like sutural ridge 
the plications of which are smooth except for microscopic incremental 
lines; whole surface of body whorl sculptured by numerous fine raised 
lines which usually alternate in size and increase in prominence 
toward the base; occasional Imes of interrupted growth and numer- 
ous very fine incremental lines also cross the body whorl. Aperture 
pyriform; canal narrow; lip simple. 
Dimensions.—Of type from which portion, of canal is missing, 
length, 26 mm.; latitude, 17.5 mm. 
Notes.—This species is allied to Agasoma barkerianum Cooper.’ 
Agasoma gravida (Gabb), and Agasoma sinuata (Gabb), the first 
two from the Vaqueros (lower Miocene), the last from the upper 
Miocene of Walnut Creek, Contra Costa County. It differs from the 
first in having a lower spire, a broader but less sharply nodose carina 
on body whorl, and in lacking the prominent nodose angles on the 
middle of the body whorl; it differs from the second in having a 
“Bull. California State Min. Bur., No. 4, p. 53, pl. v, fig. 63, 1894. 
