404 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



This is the species which by some authors has been referred to P- vitreus 

 Gineliu, from which it differs by sparser distribution of the scales and of the rows 

 of scales, and by a slight but obvious obliquity. The two forms are, however, 

 extremely similar. The " Challenger" dredged the present form in from 140 to 

 400 fathoms, off the southwest coast of Chile, or western Patagonia. 



Pecten (Pseudamusium) panamensis Dall, n. sp. 



Plate 6, flgrures 8, 10. 



Shell translucent yellowish white, very thin, resembling mica in consistency, 

 oblique, compressed ; beaks small, low, polished, hardly projecting beyond the 

 hinge line; ears small, subequal, the posterior feebly differentiated; the anterior 

 right ear with a wide fasciole corresponding to the byssal sulcus, above which are 

 five or more radial threads, the whole with stroug incremental Hues ; on the lower 

 margin of the fasciole is a hue of minute beads, apparently a ctenolium which be- 

 comes obsolete at maturity; the other ears are sculptured like the rest of the 

 disk; sculpture: on the left valve a feeble but distinct " Camptonedes" striation, 

 rather coarse and irregular incremental lines, the whole crossed by 40-65 fine 

 radial, sparsely, minutely scaly threads, the scales occurring usually at the inter- 

 section with a prominent incremental line ; left valve with similar sculpture except 

 that the " Camptonedes " striation is so fine as to require strong magnification 

 and a good light to be seen at all ; the valves are produced obliquely downward 

 and backward ; the surface sculpture yields readily to friction and many of the 

 valves have lost it altogether, retaining only the concentric sculpture ; left valve 

 slightly more convex; interior glassy, the resiliary pit very small, the margins 

 entire. Height, 18; length, 18; max. diam. 2.5; hinge line, 9.5 mm. A 

 very large specimen is 22 mm. high. 



U. S. S. "Albatross," station 3354, Gulf of Panama, in 322 fathoms, mud, 

 bottom temperature 56° F. U. S. N. Mus. 122,865. Also at stations 3389, 

 3396, 3407, and 3422, ranging from near Acapulco, Mexico, to the Galapagos 

 Islands, in 141 to 885 fathoms, soft bottom, temperatures 37''-2 to 53°. 5 F. 



The shell was very abundant at some localities, the valves dead and separated, 

 very few retaining the radial sculpture. 



CYCLOPECTEN Vkrrill. 



Pecten (Cyclopecten) rotundus Dall, n. ep. 



Siiell very small, thin, white, suborbicular, with subequal ears, both valves 

 nearly equally convex; right valve polished, minutely regularly concentrically 

 striated, which sculpture is barely visible under a hand lens ; posterior ear smooth, 

 anterior finely radially tiircadtd, with a narrow but clean-cut byssal sulcus and 

 fasciole ; left valve finely sharply radially striated, the nuterior ear finely rcticu- 



