230 ANNALS OF THE CARNEGIE MUSEUM. 
to its systematic value, the beak-sculpture, when properly understood, 
indicates certainly systematic affinity, but is not fit to be used for the 
distinction of larger groups, since it is very likely that the different 
types were developed rather early, and are found side by side among 
the more primitive groups of Najades, the Unionine for instance. 
Yet in the more advanced groups often only one type isfound. Thus, 
for instance, among the Anodontine and Lampsiline, we possess 
only the first type up to the double-looped structure, while the zig-zag 
structure is practically absent, and no trace of the other type (the 
radial) is ever found. On the other hand, it seems that in the Mu- 
telide only the radial type is present, provided there is any sculpture 
at all. In addition, conditions become yet more complex by the fact 
that the beak-sculpture in general seems to be a character which is 
subject to obliteration, and anywhere within the system we may expect 
to meet forms which have reduced their beak-sculpture to a lesser 
- or greater degree, often to complete disappearance. ‘Thus we may say, 
in a general way, that beak-sculpture, although important and in- 
dicating the minor affinities, is unfit to be used for the distinction of 
the larger groups. 
Family MARGARITANID~. 
I recognize only one genus in this family, to which a number of 
species have been assigned by Simpson, of which, however, the 
structure of four only is known. 
Genus MARGARITANA Schumacher, 1817. 
Simpson, 1900), p. 674. 
Margaritana margaritifera (Linnzus). 
Some twenty specimens are at hand, from the drainage of the upper 
Little Schuylkill River in Schuylkill County, Pennsylvania, collected 
by myself; soft parts of another specimen from the Auma creek, near 
Weida, Saxe-Weimar, Germany (drainage of Elster river); and three 
complete specimens from the Perl-Bach at Postfelden, near Falken- 
stein, Bavarian Forest, Germany. For these German specimens I am 
indebted to Mr. W. Israél. 
Published figures: Photograph of soft parts in shell, by Carl (1910, 
pl. 4, figs. A and B); of gills, by Ortmann (19110, p. 285, fig. 1, and 
pl. 87; fig: 11). 
