X. NOTES UPON THE FAMILIES AND GENERA OF THE 



NAJADES. 



By Arnold E. Ortmann, Ph.D. 



(Plates XVI 1 1 -XX.) 



In accordance with the observations recorded in a number of shorter 

 notes on the Najades published recently by the writer (Ortmann, 

 1910a, 19100, 1910c, 1910a 7 , 1911a) it is evident that the system of 

 Simpson ( 1 9000) 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, 191 lb). 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 Margaritanidce) 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; — outer gill; 



br = branchial opening; p = pes (foot); 



/ = flaps of margin of mantle; pp = papillae on margin of mantle; 

 i = inner gill; sa = supra-anal opening. 



mp = marsupium; 

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