OF THE lAMii.v or NAIADES. 121 



30. U. iris, Lea. 



40. I", zig-zag, Lea. 



41. U. pntulus, Lea. 



Conchologists have with great reason complained of the 

 extreme difficulty of identifying Lamarck's species of the ge- 

 nus Unio. Mr Banus says. "Inmost cases wherever INI. 

 Lamarck can find a difference, though by liis own account 

 • nothing remarkable? he makes a different species:" and Mr 

 Swainson declares thai -fine half the species which he has 

 enumerated" cannot be determined on account of the short 

 descriptions and want of figures. The truth of these remarks 

 I have fell severely whenever I have had occasion to consult 

 this author for the genus; and. with the hope of clearing the 

 path in a measure of those who may follow me. I propose to 

 give here the results of examinations of his species made at 

 different times with much care. 



' '. rinuata. This is the Mya margaritifera of Linnaeus 

 and oilier authors, and to which Barnes's Alasmodonta orrn- 

 ata is the analogue. Mr B. was not aware, when he descri- 

 bed it. that it was similar. He has recently, in the reclama- 

 tion of his Uniones. resigned this species of /Uasmodonta. If 

 Mr Say's genus be admitted, we must of course call this type 

 of Lamarck's I nio. .lln.sniodonta margaritifera, 



/'. dongata. There can scarcely he a douht hut that this 

 is a young shell of the above species, 



i\ crassidens, It is evident on examination of our author's 

 d< scription of this species and its varieties, and the crasmu of 

 Say and of Barnes, that all the ponderous varieties of our 

 Uniones were brought into these species, neither of which 

 can possibly stand. (See note, page 117.) 



U. peruviana. This species embraces the plieataoi L< 

 Sueur, the eratnu and undulatus of Barnes, the giganteu 

 I)r Mitchill's collection, the rariplicata and eraseideru of La> 

 paarck, and the undulata and dombeyana of Valenciennes. 



