338 MEMOIRS OF THE CARNEGIE MUSEUM 
e!, Shell rounded or ovate, without distinct posterior ridge. Color of epidermis dull, without 
color-markings, or simply with rays. Glochidia normal in shape and size. 
Genus Obovaria Rafinesque. 
e. Shell ovate or triangular, with a distinct, and often sharp posterior ridge; epidermis 
painted with broken rays, forming a pattern of lunate, squarish, or arrow-shaped 
marks; glochidia (in one species at least) rather large and with gaping margins. 
Genus Plagiola Rafinesque. 
d*, Shell not very solid, or thin, ovate, more or less compressed and winged along the dorsal 
margin (at least when young). 
e!, Glochidia of normal shape, but of unusually small size. Genus Paraptera gen. nov.” 
e*. Glochidia celt-shaped, with two spines on each valve, with gaping margins. 
Genus Proptera Rafinesque. 
b?. Inner edge of mantle in front of the branchial opening, chiefly in the female, differentiated by papille 
or flaps, and sometimes not parallel to the outer edge; male and female shells distinct, generally very 
markedly so. 
cl. Inner edge of mantle essentially parallel to the outer edge, with papille or flaps; shell ovate or 
elongate, the postbasal region of the female somewhat swollen and more rounded than in the male. 
Genus Lampsilis Rafinesque. 
c. Inner edge of mantle in the female in front of the branchial opening not parallel to the outer edge, 
but more or less remote from it, with papille; shell ovate or triangular, the postbasal region of 
the female very strongly inflated and projecting, giving to the whole shell an entirely different 
shape from that of the male. Genus Truncilla Rafinesque. 
BIBLIOGRAPHY. 
This list contains only those papers, which have been quoted in the text. 
Baker, F. C.—The Mollusca of the Chicago Area. Pelecypoda. (Bulletin Chicago 
Academy Sciences, 3, Part 1, 1898.) 
Brooks, W. K.—Handbook of Invertebrate Zoology, 1890. 
Conner, C. H.—Supplementary Notes on the Breeding Season of the Unionidee. (Nau- 
tilus, 22, 1909, pp. 111-112.) 
Cooker, A. H.—Molluses, in the Cambridge Natural History, 3, 1895. 
Harms, W.—Zur Biologie und Entwicklungsgeschichte der Flussperlmuschel. (Zool- 
ogischer Anzeiger, 31, 1907, pp. 814-824.) 
Lea, I.—Observations on the Genus Unio, Vols. 1-13, 1832-1874. (In the text I cite 
only according to volume or plate. The pagination of my copy is entirely at variance 
with the references given by Simpson.) 
LeFevre, G., and Curtis, W. C.—The Marsupium of the Unionide. (Biological Bulletin 
19, 1910, pp. 31-34.) 
Ortmann, A. E.—The Breeding Season of the Unionidee in Pennsylvania. (Nautilus, 
22, 1909, pp. 91-95, 99-103.) 
*Type P. gracilis (Barnes). 
