334 MEMOIRS OF THE CARNEGIE MUSEUM 
genus for L. gracilis. I propose here the name of Paraptera for it. Paraptera 
and Proptera are closely allied in the structure of the soft parts, and agree especially 
in the edge of the mantle.” They also have many similarities in the shell, and 
greatly differ in this respect from Obovaria and Plagiola. 
The separation of the species would leave in the genus Lampsilis the following 
species: parva, iris, nasuta, recta (forming a group with papille on the edge of the 
mantle); and ventricosa, ovata, multiradiata, cariosa, orbiculata (with a flap on the 
edge of the mantle). But I also unite with this genus Micromya fabalis, which 
does not differ in any essential point from Lampsilis, and possesses on the edge 
of the mantle the characteristic papillz of the first group of Lampsilis. 
Lastly we have the genus T’runcilla, which is not only characterized by the 
soft parts, as we have seen above, but more emphatically by the shape of the shell. 
Simpson’s division of this genus into subgenera is well supported. 
It is clear, that Truncilla and Lampsilis are the most advanced types of this 
subfamily, and that Ptychobranchus in the first line, and then Obliquaria, Obovaria, 
and Plagiola are rather primitive. Cyprogenia, Paraptera, and Proptera represent 
special modifications of this primitive type. 
We thus obtain the following arrangement of the families, subfamilies, and 
genera of the Najades found in Pennsylvania. (Compare my Preliminary Report, 
1910, p. 114.) 
1. Family MarGariranipa Ortmann (Nautilus, February, 1911). 
Diaphragm incomplete, formed by the gills; posteriorly the outer lamina of 
the outer gills not connected with the mantle for a considerable distance; anterior 
end of the inner gills separated from the palpi by a gap; branchial and anal 
openings ill-defined, and the latter not closed above; no supra-anal developed; 
gills without water-tubes, and with scattered interlamellar connections, which in 
certain places form irregular diagonal rows; marsupium formed by all four gills; 
larva a small, semicircular glochidium, without distinct hooks; shell elongated; 
sculpture of the beak concentric; hinge-teeth imperfect; epidermis blackish. 
Genus Margaritana Schumacher.” 
*°T do not understand Simpson’s description (1900, p. 567) of the edge of the mantle of Proptera, and have not seen 
anything which could be called a ‘‘thickened flap of the outer fold.” 
*1This item should be inserted in the diagnosis on account of the different structure found in the Mutelide (See Nautilus, 
January and February, 1911). 
Certain writers (See Thiele, in Brauer, Suesswasserfauna Deutschlands, Heft 19, 1909, p. 32) consider Margaritana 
the type of the genus Unio, and call Unio by the name of Lymnium Oken 1815. This is not correct, as Simpson has already 
clearly shown (1900, p. 674, footnote 1). 
