Reports of explorations and surveys, to ascertain the most practicable and economical route for a railroad from the Mississippi River to the Pacific Ocean: Vol. 5, Pt. 2

APPENDIX.
Locality.- Carmello. Miocene? [Received from John B. Trask, by whom it was collected.
W. P. B.] MATA.
MACTRA, Lin.
31. M. DIEGOANA, Con., P1. V, fig. 45.-Triangular ventricose,- inequilateral, anterior side
oblique, rectilinear; umbonal slope carinated and nearly terminal; basal margin profoundly and
regularly rounded.
Locality. San Diego. Miocene?
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, Lanm.
32. M. CONTRACTA, Con., P1. V, fig. 35.-Elongated, narrowed, anteriorly, contracted submedially; basal margin widely contracted; disk with numerous minute radiating lines.
Locality.-Monterey Co., 16 miles S. of Tres Pinos. Recent formation.
A portionof the shell remains, showing traces of fine radiating Iines. 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 extremity rounded; basal margin rectilinear.
Locality.-San Pedro. Recent formation.
PECTEN,, Lin.
34. P. DESERTI, Con.) P1. V, fig. 41.-Suborbicular, both valves convex; ribs about 23,
rounded, somewhat flattened toward the base, about as wide as the interstices, and thevalve
more convex than the opposite one; ears equal in the upper valve; left ear of lower valve extended downwards and very obliquely striated; cartilage pit profound; a submarginal channel
parallel with the upper margin.
Locality.-Carrizo creek, Colorado desert. Miocene.
ANOMIA, Lin.
35. A. SUBCOSTATA, Con., PI. 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 obsolete radii toward the base.
Locality.-Carrizo creek, Colorado desert. Miocene.
Allied to A. ufflni of the Virginia Miocene, but thicker, less expanded, and with the radii
more numerous and more rib-like.
OSTREA, Lin.
36. 0. VESPERTINA, Con., P1. V, figs. 36. 37, 38.-Ovate, subfalcate, lower valve plicated or
ribbed more or less profoundly; hinge long and wide, sharp and somewhat pointed; ligament
cavity wide, profound, minutely wrinkled; margins abrupt; cavity not very deep; muscular
impression large, impressed; upper valve flat, irregular, plicated on the margin; a submarginal
furrow, slightly impressed, crenulated towards the hinge.
Locality.-Carrizo creek. Miocene.
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