Mr. G. B. Sowerby on Hinnites. 69 



stantly, becomes pressed close to, and takes the shape of the subf 

 stances to which it adheres, and the extremely rare occurrence of 

 an opportunity of observing its byssus, may have given rise to the 

 idea of its being adherent by its outer surface to those substances; 

 whereas the contrary is really the case, as is proved by the very 

 young specimens which never have any appearance of adherent 

 outer surface. The same circumstance also occurs in the shells 

 called Hinnites by M. Defrance ; Mr. Gray's ignorance of it has 

 undoubtedly been the cause of leading him to describe them as 

 adherent by their outer surfaces and not by a byssus,* and con- 

 sequently to the incorrect situation in the system, which both 

 zoologists have assigned to them. 



I shall therefore next propose the following as an amended 

 generic character, observing that it is only in the circumstance of 

 its being apparently adherent by its outer surface, and not by a 

 byssHS, that it diflfers from Pecten. 



Fam. Pectinid^. 

 Gen. Hinnites. Defr. 



Testa bivalvis, inaequivalvis, bysso adhaereus, valvis auritis, ra- 

 diatim striatis, umbonibus externe in areas subquadrangulares 

 productis, sinu byssi parvo : cardine edentulo ; cartilagine elas^ 

 tica, oblonga, sulco utriusque valvae profundo imposita; ligamento 

 marginali, lineari ; rectiusculo. 



Shell, bivalve, inequivalve, adhering by a byssus ; valves eared, 

 radiately striated ; umbones within produced into the form of a 

 rather quadrangular area, in the centre of which is the groove for 

 the elastic cartilage ; opening between the two valves, for the 

 byssus, small: hinge without teeth, elastic cartilage + oblong, 

 placed in a deep groove in each vaJve, and considerably pro* 

 minent within the cavity of the shell : ligament marginal, linear, 



* Of the change in the name which Mr. Gray proposes, I only observe that 

 it appears to be quite unnecessary : Hinnites will serve quite as well to re- 

 present a genus of which only some of the species, as it will one of which all 

 the species are fossil. 



+ I have here adopted the terms given to the two parts of what is commonly 

 <!alled " ligament" proposed by Mr. Gray. — Dr. Leach was I believe the first 

 who pointed out these two parts and explained their functions. 



