410 NEW GENUS AND SOME NEW SPECIES 



or salmon, more generally the former : specimens are rarely 

 found with the nacre entirely coloured. The complanatus, 

 of which so many false species have been created by Euro- 

 pean naturalists, presents us with more colours and shades 

 than any other species except the cuneatus of Barnes, which 

 by many conchologists is considered analogous to it. These 

 two species present us with specimens of the darkest purple, 

 the purest white, the richest salmon, and all their intermediate 

 shades. The fine indistinct striae of the nacre, which are 

 sometimes observed to diverge from the interior of the beak 

 to the margin, are caused by the successive removals of the 

 marginal attachment of the mantle. 



It should be borne constantly in mind that the colour of 

 the nacre is an extremely doubtful character in the family 

 of Naiades; in exemplification of which I have an Anodonta 

 from the Ohio, the nacre of one valve of which is salmon and 

 the other white. The valves are beyond all doubt of the same 

 animal. The green irregular spots and marks sometimes de- 

 scribed to exist in our Uniones deserve no attention, as they 

 are altogether accidental, perhaps the effect of disease : they 

 are more frequent in the rectus and cylindricus. 



Elevations on the surface of the disks. These are sometimes 

 tuberculated, sometimes undulated ;. and our western waters 

 are the only ones we know of which produce many species thus 

 marked. There they exist in great variety and exceedingly 

 great beauty. The U. tubercidatus and U. lacrymosus pos- 

 sess more tubercles than any other species. The U. verru- 

 cosus possesses them irregularly scattered over the sides of the 

 valves. The U. metanever and U. cylindricus, besides the 

 irregular elevations over the disk, have remarkable undula- 

 tions along the umbonial slope*, from the beak to the mar- 

 gin. The U. cornutus is furnished with three or four protu- 

 berances or " horns" in a row, passing from the beaks direct 

 to the basal margin ; the varieties of the cornutus have these 



* I use this term for the elevated ridge which passes from the beaks to the pos- 

 terior margin. 



