OP THE GENUS UNIO. 273 



gin — have one distinct line of growth — cardinal tooth very 

 wide, depressed and sulcated — lamellar tooth straight, short, 

 crenated and abrupt — posterior cicatrices confluent ; anterior 

 cicatrices distinct, the great one deep and partly surrounding 

 the cardinal tooth — cavity not deep, but angular, and extend- 

 ing under the cardinal tooth — double impression of the man- 

 tle very perceptible — nacre pearly white and silvery. 



Remarks. — This rare shell forms without doubt the most 

 beautiful and perfect species yet discovered of this genus. Its 

 beautiful tubercles, lively colour and delicately pointed white 

 beaks, together with its strikingly pure nacre, entitle it to a 

 precedence over all that have yet found their way to our ca- 

 binets. The form of the tubercles is very peculiar and they 

 distinctly mark this fine species. The specimen represented 

 in the drawing is the largest of five which I have seen. 



This species is more nearly allied to the metanevra of 

 Rafinesque than to any other. It differs however, essen- 

 tially, in its having a greater number and more distinct tuber- 

 cles'; its colour, and the tuberculous ridge of the latter being 

 replaced by a smooth furrow, enlarging from the beaks to the 

 posterior basal margin and bordered by two rows of small tu- 

 bercles. The metanevra is also larger and more ponderous, 



VOL.. ni. — 3 z 



