14 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 23 



Propeamussium malpelonium (Dall) 1908 

 Plate 2, fig. 1 



AmusiuT/i (Propeamusium) malpelonium Dall, 1908, p. 405, pi. 6, 



fig. 9. 

 Amusium malpelonium Dall. M. Smith, 1944, p. 52, fig. 688 (reproduc- 

 tion of original figure). 



Holotype: U. S. National Museum. 



Type locality : Albatross station 3360, Gulf of Panama, in 1672 

 fathoms, sand. 



Original description : Shell suborbicular, of a dirty white color, very 

 thin and fragile, with small subequal ears, moderately convex ; beaks low, 

 prodissoconch small, swollen, slightly irregular, often eroded; left valve 

 with small subequal, minutely concentrically lamellose ears; posterior 

 submargin smooth or only with incremental lines; disk with fine incre- 

 mental lines crossed by numerous fine radial lines with wider interspaces, 

 increasing by intercalation; these radii are arcuate, slightly convex on 

 the anterior side, and bending gently toward the posterior; the radii are 

 not scaly; right valve flexible toward the ventral margin, the portion 

 beyond the internal lirae slightly reflexed when the valves are closed; 

 ears similar and similarly sculptured, the anterior with no byssal sulcus, 

 though there is a single feeble ray near the submargin and a slight in- 

 ward flexuosity of the incremental lines ; disk regularly concentrically 

 striated, the striae with wider interspaces, the intact surface covered with 

 a thin, dehiscent, coarsely fibrous layer; interior polished, the central 

 part whiter, with nine regular, even white, elevated lirae extending all 

 the way from the umbonal region without noticeable thickening distally ; 

 in each valve are also two short auricular crura. Height of shell, 18.2; 

 breadth, 18.5 ; hinge line, 8.2 ; diam. 3.4 mm. 



Geographical range: Known only from five Albatross stations: the 

 type locality in the Gulf of Panama; stations 3374, 3381, and 3361, in 

 the vicinity of Malpelo Island, (off western Colombia), in 1823, 1772, 

 and 1471 fathoms, respectively; and station 3684, about 640 miles north 

 of the Marquesas Islands, in 2463 fathoms. 



Bathy metric range: Recorded in 1471 to 2463 fathoms, the latter 

 depth being the greatest from which any species of Pectinidae is known. 



Ecological data : Found in sand, mud, or ooze. 



