8 



that the species known commonly by the name of Unio pur- 

 pureus, is the same with the Mytilus Jluvialilis figured by Lister, 

 t. 157, iig. 22, and described by Dillwyn, from Gmelin, under 

 that name. I have, therefore, been obliged by the rules of 

 nomenclature, now so strictly observed in Natural History, to 

 restore the original vspecific name of Gmelin to this interesting 

 shell, so well known by the name of pur pureus." (Contrib. of 

 the Macl. Lye. Vol, 1. No. 2.) 



I cannot discover any specific similarity of the purpureas to 

 this very doubtful figure, except that Lister describes it as 

 "subraber exinterna parte ;" certainly the shape of the figure is 

 more like the cariosus or ovatus Nob. than the purpureus, and 

 this assimilation is rendered more like, when we take into 

 consideration the depressed anterior margin of the shell that 

 appears associated with it on the same page, the Potamophila 

 subvirdis Grnel. But it is all mere conjecture, for even the 

 genus of the figure cannot now be determined, though it is 

 probably an Anodonta, and as the description of the Jluvialilis 

 was made out by Gmelin entirely from that figure, I should 

 consider it as worthless, as such a latitude in describing is re- 

 prehensible. 



It is nevertheless evident that, from the situation Dillwyn 

 assigns to the Jluvialilis, he considered it an Anodonta, for, ac- 

 cording to my Mss. notes wherein the 'subject of the Nayades 

 was at first discussed, he places Jluvialilis next to cygneus,andit 

 is followed by stagnaln and anatinus and fucatus, all Jinodontas. 

 Hence, if all this be correct, the rectus, triangularis or cesopus 

 are more nearly related to purpureus than the Jluvialilis can 

 be; if, indeed, such a species as the latter exists in nature. 



M. Lea observes, " Dillwyn describes this shell, under the 

 name of Mya complanata, and refers to this figure." (Lister, t. 

 150, f. 5.) "Dr. Green supposed this shell, so well known to 

 all our conchologists under Mr. Say's name purpureus, to be 

 the Mytilu? Jluvialilis described by Dillwyn from Gmelin, and 

 referred to Lister, t. 157, f. 12. I differ, however, in this 

 opinion: 1. Because it is not described as being toothed. 2. 

 Gmelin says, 'habitat in Europae aquis dulcibus.' 3. The 

 complanata answering, in description, better to our shell, and 

 being the first figured and described. It appears somewhat 

 singular to me, that the observa it and able zoologist, Mr. Say, 

 had not been struck with the similitude of our shell to Lister's 

 figure and description. There is no species more common in 

 all our fresh waters, east of the Alleghany Mountains, than 

 this; and nothing could be more likely than that it should be 

 among the first to be taken to Europe by the early voyagers 

 to America. In accordance, therefore, with the rules of no- 



