106 OBSERVATIONS ON NAIADES, 



the valve. In the cabinets of W. Cooper, Esq. and Mr R., as well as 

 my own, are specimens of U. cylindricus whose pearly teeth are beau- 

 tifully tinged with the most delicate and beautiful pink. The same 

 cabinets possess also the U. securis with the lateral tooth tinted in the 

 same manner. The U. metanever has sometimes, though very rarely, 

 a tint of pink, and still more rarely of nankeen yellow in the centre 

 of the beaks. The U. circuhs, as observed in a previous memoir, is 

 sometimes, though rarely, possessed of a pink tint. 



Whether all the species with white nacre may sometimes be poss- 

 essed of this beautiful • variety remains to be observed. These rare 

 and beautiful variations will undoubtedly, when our cabinets shall be 

 possessed of all the rare species, constitute the jewels of our collections 

 and be exceedingly sought after. 



The size to which some of the species of the Naiades grow is ex- 

 ceedingly great. I have in my cabinet the following species, of the 

 weight and size annexed: 



Inches. 



U. plicatus, length 4-6, 



U. multiplicatus 4-9, 



Symphynota alata* 4-2, 



Symphynota complanataf 5-1, 



Nearly all the specimens which I have seen of the U. sokniformis 

 (nobis) were sent from Louisville. It struck me as somewhat singu- 

 lar, that a species so fragile should exist about the falls of a large river, 

 the force of whose waters there is well known. In explanation of 

 this, I have been informed by Mr T. W. Taylor of that city, that they 

 are foimd to congregate under large flat stones. Unacquainted with this 

 fact he searched in vain for a long time without finding a single alive 

 specimen, while odd valves were not uncommon. They were first 

 discovered in this situation by raising a stone to take a common craw- 

 fish, which had taken refuge there. This character seems to be pecu- 

 liar to this species. 



My sister, Mrs Febiger of Cincinnati, mentioned to me a pe- 



* Unio alatus, Say. t Alasmodonta complanata, Barnes. 



