522 ORTMANN— NAYADES OF 



In this connection it should be noted that Lewis's " Holston 

 River" actually is the Tennessee River below Knoxville (chiefly in 

 the region of Concord). Indeed, even at present, the natives in Con- 

 cord call the river there " Holston " ; but the maps of the U. S. Geo- 

 logical Survey give the name Tennessee to the river below the junc- 

 tion of the Holston (proper) and French Broad. In Knoxville the 

 river is called Tennessee. 



Aside from Lewis's paper, only a few are at hand which con- 

 tribute to the fauna of this region. One of them has been published 

 by Pilsbry and Rhoads (1896). This is, however, by no means a 

 synopsis, containing hardly half of the forms which are found here. 

 But on account of the good locality-records it is very valuable; in 

 fact, it is, up to the present time, the most accurate publication in 

 this respect. And further, two preliminary papers have been pub- 

 lished, based upon my own collections; one by myself (Ortmann, 

 19136), the other by Goodrich (1913). These, however, treat only 

 of the headwaters-region of Powell, Clinch, and Holston in Virginia. 



In addition to the material collected by myself, I have examined 

 the upper Tennessee shells in the collection of Mr. B. Walker in De- 

 troit, and I want to express to Mr. Walker my best thanks for the 

 privilege of examining his shells, and the delightful days I spent in 

 his home in April, 1916. Mr. Walker has a great number of shells 

 from this region obtained from older collections, which in part are 

 cotypes, topotypes, or other authentic material. But the greatest 

 treasure in his collection are the Nayades collected by Professor Dr. 

 C. C. Adams in 1899 to 1901, in the course of his work on lo, be- 

 cause Professor Adams always was very careful in recording his 

 localities. 



A large number of the " species " described by Lea (generally 

 from very insufficient material), and of those listed by Lewis, are 

 synonyms. Additional species have been subsequently described by 

 various authors ; but also these are mostly synonyms. There is a 

 rule, observed in many cases, and indicated first by Wilson & Clark, 

 '14, that one and the same shell assumes different shapes in the large 

 rivers and in small streams and headwaters, a rule the existence of 

 which will be shown elsewhere ; and it is easily understood why the 

 various local races have been regarded as good species, as long as 



