94 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 23 



Plagioctenium Dall, 1898, p. 696. [Proposed as a section of Chlamys.] 

 Type-species: Pecten circularis Sowerby, 1835, p. 110. "Hab. ad 

 Sinum California (Guaymas)." [= Pecten ventricosus Sowerby, 

 1842, designated as type-species by Dall.] 

 Coryjnbichlamys Iredale, 1939, p. 367. 



Type-species: Chlamys corymbiatus [jfc] Hedley, 1909, p. 423, 

 pi. 36, figs. 1-4. ". . . generally distributed in tropical Queensland." 



Original diagnosis: Le nouveau vocable subgenerique Argopecten 

 pourra s'appliquer aux especes du grand groupe des Pecten ronds, epais, 

 solides, quelquefois grands, equigibbeux, a cotes nombreuses et imbri- 

 quees et a coloration riche, pourpree, ornee de taches et de nuages viola- 

 tres. Les P. pallium, gibbus et bien d'autres especes vivantes exotiques, 

 comme aussi les P. dubius, scabrellus fossiles, etc. rentrent dans ce 

 groupe. 



Translation : The new subgeneric name Argopecten is applied to 

 species of a large group of Pectens which are round, stout, solid, some- 

 times large, equigibbous, the ribs numerous and imbricated and the 

 coloration rich, purple, ornamented with spots and clouds of violet. 

 P. pallium, gibbus, and other living exotic species, also fossils like P. 

 dubius, scabrellus, etc., belong to this group. 



Additional diagnosis: Shell moderately to deeply convex, right 

 valve more so than left in most species ; usually rather thick ; type-species 

 and several others obliquely orbicular, remaining species orbicular or 

 nearly so ; ribs strong, and in some species radially ridged ; concentric 

 lamellae present between ribs of most species, occasionally crossing ribs, 

 and often quite profuse ; all species but irradians Lamarck and purpiira- 

 tus Lamarck with well-developed hinge armature, cardinal (or linear) 

 crura and provinculum being prominent, crura often so strong as to lock 

 valves tightly. 



Remarks: As type-species of Argopecten Monterosato selected 

 Pecten solidulus Reeve (1853, sp. 155; "Hab.— ?"), citing P. Philippii 

 Recluz as a synonym and remarking that the synonymy was "probably 

 contestable." It is certainly contestable. First, solidulus is not identical 

 with Philippii Recluz, as will be shown below; second, it is peculiar 

 that he cited Philippii Recluz in 1889, for in 1875 he had renamed that 

 species commutatus because of Michelotti's prior usage of Philippii. His 

 synonymy was also regarded as erroneous by Dautzenberg & Fischer 

 (1906, p. 59) and Gignoux (1913, p. 370). 



The shell Reeve described as solidulus was from an unknown local- 

 ity; also it was a juvenile, as were the holotypes of a number of his 



