j^,i,^ of MciftuskE 



Sectional library 



MEMOIRS 



Ob ""lIK 



CAENEGIE MUSEUM 



Vol. VIII. No. 1. 



A MONOGRAPH OF THE NAIADES* OF PENNSYLVANIA. PART III. 

 "^SYSTEMATIC ACCOUNT OF THE GENERA AND SPECIES.^ 



By Arnold E. Ortmann, Ph.D., Sc.D. ^ 



(Plates I-XXI.) _ 



Introductory. 



In the first part of this monograph (Ortmann, 19116),- certain anatomical 

 features hitherto but httle investigated were considered {I. c, Pt. I, p. 282 flF.), 

 and their bearing upon the rearrangement of the system of the Naiades was dis- 

 cussed in Part II {I. c, pp. 322 ff.). At the end of Part II, a key for the genera 

 was attempted (pp. 335-338). Since then additional material, chiefly representing 



* In Parts I and II of this Monograph, which appeared in the Memoirs of the Carnegie Museum, 

 Vol. IV, No. 6, I employed the term Najadcs, following the usage of certain well-known authors who 

 have written upon this group. The spelling of this word gix^eii l^y Lamarck, who first employed it, was 

 Nayades, and this would have priority according to a strict application of the laws governing nomen- 

 clature, were it not for the fact that the Lamarckian term plainly is an error in transcription from the 

 original Greek, which is Nai'dSes. I, believe that when a Greek word is used it ought to be transcribed 

 as nearly as possible in conformity with philological usage, and therefore have reverted to the form 

 Naiades, which is not only good Greek, but sanctioned by the usage of a multitude of other authors. 

 The chief end of the " law of priority " is not to preserve and perpetuate mistakes in spelling, even when 

 made by men as eminent as Lamarck. 



' This paper is in continuation of the papers published in the Memoirs of the Carnegie Museum, 

 Vol. IV, No. 6, 1911. 



^ The references given in the text refer to the bibliography at the end of thi- paper. 



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