APPENDIX. E 325 
Locality.—Carmello. Miocene? [Received from John B. Trask, by whom it was collected.— 
PB] 
MACTRA, Lin. 
31. M. DIEGOANA, Con., Pl. V, fig. 45.— Triangular ventricose, inequilateral, anterior side 
oblique, rectilinear ; umbonal slope carinated and nearly terminal; basal margin profoundly and 
regularly rounded. 1 
Locality.—San Diego. Miocene? i 
This species is nearly allied to M. albaria of the Oregon Miocene, which probably belongs to 
the same rock as the present species. The concentric ridges represented in the figure are caused 
by weathering, as the disk was originally smooth. 
MODIOLA, Lam. 
32. M. CONTRACTA, Con., P1. V, fig. 35.—Elongated, narrowed, anteriorly, contracted sub- 
medially ; basal margin widely contracted ; disk with numerous minute radiating lines. 
Locality. —Monterey Co., 16 miles S. of Trés Pinos. Recent formation. 
A portionof the shell remains, showing traces of fine radiating lines. Miocene? 
MYTILUS, Lin. 
33. M. PEDROANUS, Con., Pl. V, fig. 40.—Oblong-subovate, ventricose, dorsal line ungulated 
medially, angle rounded; beak projecting slightly beyond the basal margin; posterior ex- 
tremity rounded ; basal margin rectilinear. 
Locality.—San Pedro. Recent formation. 
P CTEN, Lin. ۱ 
34. P. DESERTI, Con.) Pl. V, fig. 41.—Suborbicular, both valves convex; ribs about 23, 
rounded, somewhat flattened toward the base, about as wide as the interstices, and the valve 
more convex than the opposite one; ears equal in the upper valve; left ear of lower valve ex- 
tended downwards and very obliquely striated ; cartilage pit profound ; a submarginal channel 
parallel with the upper margin. 
Locality.— Carrizo creek, Colorado desert. Miocene. 
1 AOMA, in. 
3 35. A. SUBCOSTATA, Con., Pl. V, fig. 34.—Obtusely ovate, thick in substance, umbo of larger 
: valve ventricose, hinge thickened ; surface of this value obtusely undulated, concentrically and 
marked with waved, wrinkled, very irregular interrupted ribs, not much raised except toward 
the base, where they are larger and somewhat tuberculiform, upper valve entire, or with obso- 
lete radii toward the base. 
Locality. — Carrizo creek, Colorado desert. Miocene. 
Allied to A. Rufini of the Virginia Miocene, but thicker, less expanded, and with the radii 
more numerous and more rib-like. 
OSTREA, Lin. 
36. o. VESPERTINA, Con., Pl. V, figs. 36. 37, 38.—O vate, subfaleate, lower valve plicated or 
ribbed more or less profoundly ; hinge long and wide, sharp and somewhat pointed ; ligament 
3 cavity wide, profound, minutely wrinkled; margins abrupt; cavity not very deep ; muscular 
lmpression large, impressed ; upper valve flat, irregular, plicated on the margin; a submarginal 
furrow, slightly impressed, crenulated towards the hinge. 
Locality.—Carrizo creek. Miocene. 
