CLASS PELECYPODA 
59 
Type in the Boyce collection. Type locality, Santa Barbara, California. 
Range. Santa Barbara, California, to Cape San Lucas, Lower Cali¬ 
fornia. 
Subgenus Pseudamusium H. & A. Adams, 1858. 
Shells small, thin, more or less translucent; the sculpture, if any, 
feeble; inner face of the disk without lirae; disk with or without Campto- 
nectes striations, frequently with concentric imbrication. (Dali.) 
Type. Pecten exoticus Chemn. 
Distribution. Alaska; South Atlantic. 
Pecten randolphi Dali, 1897. 
Plate 14, figs. 5, 6. 
The Nautilus, 11; No. 8:86. Proc. U. S. N. M., 24; pi. 40, fig. 2. 
Shell small, thin, glassy, unsculptured, except by minute (campto- 
nectes) striation which covers both valves, and more or less obscure 
concentric undulations which are most distinct on the right valve near the 
umbo, and in some specimens altogether absent; hinge straight and short, 
anterior ears distinct, posterior ears not defined by any fold or sinus, 
outline suborbicular, valves compressed, especially the right one; right 
anterior ear with 6 small imbricated radii above, below a wide, trans¬ 
versely striated fasciole derived from a well-marked byssal sinus; 
ctenolium with 4 or 5 functional spines. Length 27.5 ; height, 26; diameter, 
5 mm. (Dali.) 
Type in U. S. N. M. Type locality, off Destruction Island, Wash¬ 
ington, in 516 fathoms. 
Range. Bering Sea to Guaymas, Mexico. 
Pecten tillamookense Arnold, 1906. 
U. S. Geol. Survey, Prof. Paper, No. 47:139; pi. 48, figs. 3, 3a. 
Shell resembling P. randolphi in outline and general characteristics. 
Disk ornamented by numerous more or less prominent, fine radiating 
ridges, microscopic radiating striae, and incremental lines of varying promi¬ 
nence. The radiating ridges are narrow and thread-like, and appear to be 
more prominent anteriorly and near the lines of interrupted growth; the 
ribs are affected similarly to the disk by the interruptions in growth. The 
microscopic striae cover the whole surface of the disk and ribs and in a 
general way radiate from the umbo, but seldom parallel to the ribs; on 
the portion of the disk and ear posterior to the umbo the striae are 
perpendicular to the lines of growth and are thus nearly parallel and not 
radiating. The right anterior ear has from 6 to 12 prominently imbricated 
radials. Length, 30; height, 30; diameter, 7 mm. (Arnold.) 
