OF THE FAMILY OF NAIADES. 409 



Colour. The colour of the Uniones is generally a decep- 

 tive character. This, however, is not always the case, and 

 therefore it deserves the attention of the conchologist. In some 

 species it is permanent in the nacre, in others it is permanent 

 in the epidermis. In the following species I have always found 

 the nacre to be white and pearly, viz. cornutus, tuhercula- 

 tus, siliquoideus, ventricosus, ovaius, triangularis, parvus, 

 plicalus, metanever, sesopus, scalenius, cylindricus* , lacry- 

 mosus, in-oratus*, ellipsis-^, donaciformis, calceolus, hetero- 

 do7i, multiradiatus, occidens, securist, iris, zig-zag, patulus, 

 and plamdatus: the last eight herein described. In the 

 ^'■torsa" of Rafinesque, and sulcafus (herein described), the 

 purple is permanent and generally dark. In the suhten- 

 tus, lanceolatus, and ruhiginosus (herein described), it is a 

 pale salmon colour, and in the ater (herein described) it 

 is a pink bordering on purple. The gibbosus is generally a 

 dark purple or chocolate, but varies from this through all the 

 intermediate shades to perfect white. The verrucosus is 

 either chocolate or white, and does not seem to enjoy the in- 

 termediate tints. The circulus (herein described) is gene- 

 rally of a pure pearly white, but sometimes, though rarely, 

 possesses a blush of pink in the centre of the valve. The 

 mytiloides presents all the shades from the deepest flesh co- 

 lour to the purest white. The cariosus is generally white, 

 but sometimes is found of a deep salmon and the intermedi- 

 ate shades. The nasutus is either pearly white or approach- 

 ing salmon colour under the beaks. The rectus is gene- 

 rally of a beautiful porcelanic white, sometimes tinted about 

 the cardinal teeth and in the cavity of the beaks with purple 



* The cylindricus and irroratus sometimes, in very perfect specimens, present 

 a slight golden appearance in tlie nacre at the anterior margin. 



t Var. a being herein described as a new species. 



I This is Rafinesque's " U. depressa" but the name being preoccupied by 

 Lamarck, apparently without the knowledge of Mr R., I am compelled to give it 

 a new name or leave it out of the catalogue. I prefer the former alternative, as 

 it is a distinct and beautiful species, and well known to most of our conchologists 

 under its duplicated name " dcpressa." In this I act in accordance with the 

 rules of nomenclature in natural history. See description, 



