MEMOTRS 
CARNEGI Ge MUSEUM: 
VOL. IV. Dan we NO. 6. 
A MONOGRAPH OF THE NAJADES OF PENNSYLVANIA. 
By Arnotp E. Ortmann, Px.D. 
GENERAL INTRODUCTION. 
The writer began to collect Najades in Pennsylvania as early as 1904. Ad- 
ditional material was incidentally secured in 1905 and 1906, while he was hunting 
for crawfishes. In 1907 the collecting of mussels was systematically begun, and 
the particularly favorable seasons of 1908 and 1910, and in part also of 1909, 
permitted the taking of large numbers of species and specimens. Not only the 
shells but also the soft parts were collected, and the writer endeavored to find 
both males and females, the latter in the sterile as well as in the gravid state. 
In this he generally was successful, and a great quantity of material representing 
the soft parts was preserved in alcohol, partly with the shell, partly without, but 
always with the proper records. In this way a collection of the Pennsylvanian 
Najades, both of shells and soft parts, has been brought together, which certainly 
is superior to any other local collection; in fact, the writer believes that he has 
at his command a larger assemblage of the soft parts than is found in all other 
collections combined. 
The chief purpose of this work was to secure the material for a systematic 
monograph of the Najades of our state. A preliminary list of the species found 
in Pennsylvania has been previously published (Ortmann, 1909), but since then, 
further information has been obtained with respect to the systematic and zodgeo- 
graphical side of the subject, and in the present monograph a final account will be 
given. In addition, the writer has investigated the anatomical structure of the 
mussels, and very important structural features, chiefly in the gills, have been 
discovered, which had been in part entirely overlooked by previous authors. The 
knowledge of the anatomical details thus obtained has enabled the writer to revise 
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