N0.12GJ. ILLUSTRATIONS OF AMERICAN SHELLS— BALL. 559 
PECTEN RANDOLPHI Dall. 
Plate XL, fig. 2. 
Pecten randolphi Dall, Nautilus, XI, No. 8, Dec. 1897, p. 86. 
Occurring in deep water from Bering- Sea to west Mexico, in from 
225 to 1,005 fathoms, U. S. Fish Connnission steamer Alhairosx. The 
figured specimen is from west of Destruction Island, State of Wash- 
ington, in 516 fathoms, bottom temperature 38- F. U.S.N.M., 107749. 
The shell is subtrauslucent white, glassy, and extremely thin. It 
l)elongs to the section Pseudaiivwiluin. 
PECTEN DAVIDSONI Dall. 
Plate XL, figs. 5, 6. 
Pecten davidsoni Dall, Nautilus, XI, No. 8, Dec, 1897, p. 86. 
Bering Sea and the Aleutian Islands and eastward to Kadiak Island, 
Alaska, in 280 to 351 fathoms. U.S.N.M., 107747. 
Shell waxen white, having the aspect of 2^ PropeamimluDi externally, 
but really belonging in the section Pi<eadamiifihim. It is named in 
honor of Prof. George Davidson, the distinguished geographer and 
astronomer of San Francisco, California. 
CRENELLA MEGAS, new species. 
Shell elongate-oval, inflated, thin, white, slightly perlaceous inter- 
nally; beaks small, low, anteriorly directed; surface very closely, finely, 
evenly, radially threaded, the threads crossed by finCj less obvious, 
incremental lines emphasized at the resting stages; margins very finely 
crenulate internally; ligament long, produced within the hinge line to 
the apex of the beaks, seated on a very thin elongate nymph, which in 
the absence of the ligament looks like a long lateral tooth or lamina; 
hinge line interrupted by the ligament; muscular impressions obscure. 
Alt. 25.5; lat. 17.0; diam. 16.5 mm. 
■ Dredged at station 2795, in Panama Bay, at a depth of 38 fathoms, 
sand, bottom temperature 64-'-' F., by the U. S. Fish Commission 
steamer Alhatnm. U.S.N.M., 96256. 
This is by all odds the largest CreneUa known. It is very delicate 
and basally the oval profile is attenuated. Only one valve was obtained. 
The hinge line is not strongh' crenulated, owing to the delicac}^ of the 
ladial threading. 
LIMOPSIS PANAMENSIS, new species. 
Shell small, moderately convex, of a pale slate color, covered with 
a dark blackish brown pilose periostracum more or less disposed 
in radiating lines; beaks low, plump; hinge area narrow, with a well- 
marked fossette; interior of shell dull bluish white, with six posterior 
