56 
MARINE SHELLS OF WEST COAST OF NORTH AMERICA 
omous after reaching a length of about 30 mm.; interspaces deeply 
channeled and narrower than ribs; anterior ear imperfectly radially ribbed 
with 6 ridges, and showing about 4 ribs; byssal notch not deep. Left 
valve with 25-30 narrow convex ribs, showing imbricating sculpture only 
slightly; interspaces as wide as or wider than ribs; after a diameter of 
30 mm. has been reached by the left valve small intercalary ribs appear 
in most of the widening interspaces; anterior ear with 5 narrow imbricat¬ 
ing ridges separated by wide interspaces. Both valves show a tendency 
to contract suddenly at the basal margin upon nearing completion of 
growth; surface of both valves covered with a minute lattice-like sculpture, 
which is generally worn off on exposed portions of the shell. Alt., 45; 
long., 42; hinge line, 18; diameter 15 mm. (Arnold.) 
Type in U. S. N. M. and described from a fossil. Type locality, 
Pliocene, of San Pedro, California. 
Range. Puget Sound. In the Pleistocene and Pliocene of Santa 
Barbara, San Pedro, and San Diego. 
Pecten paucicostatus Carpenter, 1864. 
Plate 41, figs. 4, 5. 
Suppl. Rep. Brit . Assoc., p. 645. Arnold, Tort. Pectens Cal.; pi. 39, figs. 3, 4. 
P. testa subconvexa, vix sequilaterali; castaneo seu rubido seu 
electrino picta; costis xi.-xv., validia, angustis, rotundatis; interstitiis 
multo latioribus, subplanatis; tota superficie minutissime concentrice 
striata; auriculis latis, haud asqualibus, lirulis circ. vi. ornatis; sinu 
paucidentato; intus pallidiore, linea cardinis costata, ad suturas auricu- 
larum tuberculossa; fossa ligamentali curta, transversim lata. Long., 1.7; 
lat., 1.84; alt., .56. (Carpenter.) 
Shell averaging about 35 mm. in altitude, longer than high, subequi- 
valve, moderately ventricose; thick shelled; margins smooth. Right valve 
subequilateral, slightly more ventricose than the left; ribs 12 to 14, 
prominent, convex-topped, subangular; interspaces slightly wider than 
the ribs, somewhat rounded incremental sculpture fine and regular, not 
looped; hinge line about five-sevenths length of disk; ears moderately 
prominent; anterior ear with about 5 prominent radiating ridges and 
numerous incremental lines; byssal notch prominent; posterior ear similar 
to anterior in sculpture, except that it is not quite so pronounced as in 
the latter. Left valve with prominent subangular ribs, slightly narrower 
than those of the*right valve; interspaces correspondingly wider and flat- 
bottomed; ears similarly sculptured to those of right valve. (Arnold.) 
Type in the Boyce Collection, Utica, New York. Type locality, Gulf 
of California. 
Range. Santa Barbara, California, to the Gulf of California. 
