OF THE FAMILY OF NAIADES. 409 



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

 tive character. This, however, is not always the ease, 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 1 have always found 

 the nacre to be white and pearly, viz. cornufus. lularculu- 

 /us. sMquoideus, rni/rirosiis. oral us. triangularis, parvus, 

 p/icufus. mi /(Dim r. tesopus, scalenius, eyKndrious*, Ittmj- 

 niosus. irrorulus'. effipsisf, itonaciforniis. culrtolus. luh ra- 

 tion, mttltiradiatus, occidens, sicurisi. iris, zig-zag. jxi/ulus. 

 and plunululus: the last eighl herein described. In the 

 •■forsu" of Rafinesque, and sulrafus (herein described), the 

 purple is permanent and generally dark. In the mbten- 

 tus. lanciolalus. and rubiginosus (herein described), it i- a 

 pale salmon colour, and in the uttr (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 tli^ shades from the deepest flesh co- 

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

 hut sometimes i> found of a deep salmon ami the intermedi- 

 ate -hades. Tin- 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 

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



* The riilinilri'ru.i and irranitiis sometimes, in M-rv perfec ns, present 



i -liL'lit golden appearance in the nacre at the anterior mai 



t Var. a being herein described as a m h 



| This ib Rafinesque's " I depretta" but the name bein upied by 



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



a new na r leave ii oul of tin catalogue. I prefer the former altern itive, ■ 



it in a distinct mil beautiful species, ami well known to most of oui 

 under its duplicated name " depretta." In wis! act in accordance with 

 of nomenclature in natural tnstorj Bee description. 



