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 Unio pur pur eus, is the same 
with the Mytilm Jiuviatilis 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 Mad. Lyc. Yol 1. No. 2.) 
I cannot discover any specific similarity of the purpureus to this 
very doubtful figure, except that Lister describes it as suhruher 
ex interna parte certainly the shape of the figure is more like 
the cariosus or ovatus, nob., than ihe 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 Potamophila suhviridis, Gmel. Biit 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 jiuviatilis 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 Jiuviatilis, he considered it an Anodonta, for, ac- 
cording to my MSS. notes, wherein the subject of theiVa^ac^eswas 
at first discussed, he places Jiuviatilis next to cygneus, and it is 
Jollowed hy stagnalis and anatinus and Jucatus, all Anodontas. 
Hence, if all this be correct, the rectus, triangularis or msopus are 
more nearly related to purpureus than the Jiuviatilis can be j if in- 
deed, such a species as the latter exists in nature. 
Mr. Lea observes, Dillwyn describes this shell, under the name 
of Mya 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 Jiuviatilis, 
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 
