by William Swainson, Zoological Illustrations — Vol I. Pl… (1820)
“ The colours of all are more or less dark-brown, sometimes radiated with green; but the specific characters rest on the contour of the shell and the proportion of the teeth.There can be no doubt this shell is the Unio nasutus of Say, who refers to the figure of Lister. The Unio nasuta however of Lamarck I apprehend will be found different, as he seems to think; his shell also is purple inside with short thick teeth; indeed so much uncertainty hangs on the shells of this genus, that the species can only be fixed by ample descriptions and very correct figures. ”
