135 



Unio purpureus, nob. — The propriety of retaining this name 

 has recently been much questioned by two of our conchologists, 

 but as I do not think that, as yet, its stability is in any degree 

 problematical, I shall endeavor to show on what my opinion is 

 founded. Prof. Green remarks, " I have no doubt that the spe- 

 cies known commonly by the name of Uhio jnirpureiis, is the same 

 with the Mytilus JiuviatiUs figured by Lister, t. 157, fig. 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 specific name 

 of Gmelin to this interesting shell, so well known by the name of 

 purpureus." (Contrib. of the Macl. Lye. Vol 1. No. 2.) 



I cannot discover any specific similarity of the purpureus to this 

 very doubtful figure, except that Lister describes it as " suhruber 

 ex interna parte ;" certainly the shape of the figure is more like 

 the cariosus or ovatus, nob., than \h.Q purpureus, and this assimila- 

 tion 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 PotamopMla suhviridis, Gmel. But it is 

 all mere conjecture, for even the genus of the figure cannot now 

 be determined, though it is probably an AnodoDita, and as the 

 description of the fiuviatilis was made out by Gmelin entirely from 

 that figure, I should consider it as worthless, as such a latitude in 

 describing is reprehensible. 



It is nevertheless evident that, from the situation Dillwyn 

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

 cording to my MSS. notes, wherein the subject of the iVayacZes was 

 at first discussed, he places fiuviatilis next to cygneus, and it is 

 followed hy stagnalis and anatinus and fucatus, all Anodontas. 

 Hence, if all this be correct, the rectus, triangularis or sesopus are 

 more nearly related to purpureus than the fiuviatilis can be ; if in- 

 deed, such a species as the latter exists in nature. 



Mr. Lea observes, " Dillwyn describes this shell, under the name 

 of 3fya complanata, and refers to this figure." (Lister, 1. 150, f. 5.) 

 '' Dr. Green supposed this shell, so well known to all our concholo- 

 gists under Mr. Say's name purpureus, to be the Mytilus fiuviatilis, 

 described by Dillwyn from Gmelin, and referred to Lister, t. 157, 

 f. 12. I difier, however, in this opinion : 1. Because it is not 

 described as being toothed. 2. Gmelin says, " habitat in Europae 



