PEDUM. 



Genus PEDUM, Bruguiere. 



Testa longittuUnalk vel cnneiformis, compressa, inaquivalvis, 

 subauriculata; valvd in/eriore convexiuseuld, ad latera 

 refiexd, prope cardiiiem profundi sinuatd, valvd supe- 

 riore pland. Cardo edentulua, ligamento partim ex- 

 terna infosmld canaliformi sub aream prodiictam vaha 

 inferioris. 

 Shell longitudinal or wedge-shaped, compressed, inequi- 

 valve, slightly eared ; lower valve rather convex, re- 

 flected at the sides, deeply sinuated near the hinge, 

 lower valve flat. Hinge toothless, with the ligament 

 partially external contained within a channelled pit 

 running across a produced area of the lower valve. 

 The earliest publication of the shell which forms the 

 subject of this genus was the mention of " a rare Oyster 

 from the Indies," nearly a hundred years ago, in the 

 'Catalogue Eaisonne' of Davila. Gmelin and Chemnitz 

 observing, almost simultaneously, its resemblance to Spon- 

 dylus, named it " the Spondylus-like Oyster, Ostrea Spon- 

 dyloideum ;" but Bruguiere, while establishing some impor- 

 tant improvements in the clnssification of shells in the 

 • Encyclopedie Methodique,' perceived the remarkable pe- 

 culiarities of this so-called Oyster, and founded the genus 

 Pedum for its special reception. Until lately this shell 

 continued to be one of great rarity. It has now, however, 

 been found in comparative abundance in the Ked Sea, im- 

 bedded chiefly in masses of madrepore. No second species 

 has been discovered. 



The animal of Pedmn, according to the observations of 



MM. Quoy and Gaimard, made during the voyage of the 

 'Astrolabe,' partakes of the character of those of /^;oMf/^te« 

 and Pecten, but its shell is quite unique in structure, 

 being slight in substance, reflected at the sides, and hav- 

 ing, with its ligamentary area, an unusually deep sinus for 

 the passage of the byssus. 



Species 1. (Fig. a, 4, c, d, e, Mus. Cuming.) 

 Pedum Sponuyloideum. Fed. testa longitudinaliter vel 

 ovato-cmieiformi, planulatd, superiore longitudinaliter 

 striata, striis granulato-scalris ; alba, purpureo-rufo 

 plus mimes tinctd et transversim fasciatd. 

 The Spondylus-like Pedum. Shell longitudinal or 

 ovately wedge-shaped, flat, upper valve longitudi- 

 nally striated, striae granulately scabrous; white, 

 more or less stained and transversely banded with 

 purple-red. 

 Ostrea Spondyloidea, Gmelin, Syst. Nat. 13th edit. p. 3335. 

 Hah. Red Sea (in madrepore). 



Of the specimens of this well-known and interesting 

 shell represented in the accompanying Plate, Pig. 1 a 

 illustrates its early stage of growth, while Pig. 1 d is a 

 fine adult, and Fig. 1 c similarly adult, but a dwarf variety. 

 Pig. 1 (/ is a chai-acteristic white variety, almost uniformly 

 more rounded than the typical form ; and Pig. 1 e shows 

 a mass of madrepore with a young Pedum in its natural 

 habitat. 



November, 1858. 



