Reprinted from ANNALS OF THE CARNEGIE MuseuM, Vol. VIII, No. 2, 1912.1 
X. NOTES UPON THE FAMILIES AND GENERA OF THE 
NAJADES. 
By ARNOLD E. ORTMANN, PH.D. 
(Plates XVIII-XX.) 
In accordance with the observations recorded in a number of shorter 
notes on the Najades published recently by the writer (Ortmann, 
1910a, I910b, 1910c, 1910d, 1911a) it is evident that the system of 
Simpson (19000) should be thoroughly revised, and that the soft 
parts of every species of mussels should be studied. In preparation 
for a monograph of the Najades of Pennsylvania this has been done 
by the writer, and the general results have been recently published 
in the first part of this work (Ortmann, 1911). But since it will take 
some time before the subsequent parts, dealing with the single species, 
will be ready for publication, and since the writer has examined, in 
addition, a great number of species not found in Pennsylvania, it 
seems well to publish these results as early as possible, combining the 
same with an attempt to rearrange the system to suit the new points 
of view. In the present paper, a general synopsis of the system will 
be given, in it assigning to each species, which has been examined, its 
proper place. 
Remarks as to the Figures.—For the majority of the genera, text- 
figures have been introduced to illustrate their principal characters. 
If possible, the type-species has been selected. These figures have 
been drawn from actual specimens, and are about natural size, but 
they have been generalized and are of a diagrammatic character, the 
chief features being emphasized. This refers chiefly to the gill-fila- 
ments (where they are given, as in the Margaritanide@) and the septa. 
The latter always are heavier than in nature, to bring out their charac- 
teristic features. In all figures the lettering is uniform, and the letters 
have the following meaning: 
an = anal opening; o = outer gill; 
br = branchial opening; pb = pes (foot); 
f =flapsof margin of mantle; pp = papille on margin of mantle; 
1 = inner gill; sa@ = supra-anal opening. 
mp = marsupium; 
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