COMPLETE GRAU : PECTINIDAE OF THE EASTERN PACIFIC 95 



Other species. After describing it he remarked, "This has the appearance 

 of a young P. gibbosus {lapsus calami for gibbus], but it is distinct." 

 F. K. North examined the holotypes of solidulus and Philippii in the 

 British Museum and told the author that he found them to be quite 

 distinct, a particularly noticeable difference being that the auricles of 

 solidulus are proportionately about three times the size of those of 

 Philippii. In the literature of the 18th and 19th centuries drawings were 

 usually stylized to the detriment of scientific accuracy. Since no addi- 

 tional specimens referable to P. solidulus have ever been reported, it is 

 quite probable that the original was a specimen of some previously 

 described species. Judging from Reeve's figure, the shell might be a 

 juvenile Ostrea gibba Linne (1758, p. 698), Ostrea flabellum Gmelin 

 (1791, p. 3321), Pecten circularis Sowerby, or even P. purpuratus 

 Lamarck. 



It is more than likely that Monterosato never saw the holotype of P. 

 solidulus, but since he was obviously familiar with P. commutatus ( = 

 P. Philippii Recluz), it would seem safe to assume that he based Argo- 

 pecten on the characters of that species and intended it to be the type- 

 species, erroneously regarding it as identical with (and a synonym of) 

 the earlier solidulus. 



While we can realize from the type-species Monterosato's intention 

 in erecting Argopecten, his diagnosis is inapplicable in two respects, and 

 he was, of course, mistaken in referring "P. pallium' to his new sub- 

 genus. The ribs in Argopecten seldom have imbricating sculpture, and 

 any restriction as to coloration is unrealistic in a subgenus comprising a 

 number of species and subspecies. "P. pallium" {Ostrea pallium Linne, 

 1758, p. 697) is obviously generically distinct from P. commutatus, and 

 was so well known even in Monterosato's time that only carelessness 

 would seem to account for his mention of it. 



Aequipecten was proposed by Fischer (1886, p. 844) with a very 

 brief diagnosis: "Forme circulaire; cotes rayonnantes bien marquees." 

 Here again we can realize the author's intention by the type-species he 

 designated, in this case Ostrea opercularis Linne (1758, p. 698). Al- 

 though various authors have referred to Aequipecten such species as 

 Ostrea gibba Linne, Pecten irradians Lamarck (1819, p. 143) and 

 P. circularis Sowerby, it is obvious that they can not be cogeneric with 

 O. opercularis. Argopecten differs from Aequipecten in the following 

 respects : the convexity of both valves is greater, the right shell is thicker, 

 ribs stronger, hinge armature almost always more pronounced, concentric 

 (rather than radial) lamellae often present, and a tendency toward 

 obliquity is quite common. 



