534 ORTMANN— NAYADES OF 



drainage of North Alabama, and, also here, cor is in the Tennessee 

 proper and the lower parts of the larger tributaries (Elk, both Flint, 

 and Paint Rock Rivers), while in the upper parts, at least of Paint 

 Rock River, it passes into the aiialoga-iorm. 



Group of Fusconaia barnesiana (Lea). 



Forms of this group have been listed by Lewis ("71) as U. bar- 

 nesiamis, pudicus, and tumescens. In Simpson's papers ('00 and 

 '14), they stand under Pleiirobenia, and their proper position and 

 mutual relation have not at all been understood. 



All these shells belong to Fusconaia, but form a separate group 

 within this genus, distinguished from the other species by very shal- 

 low beak cavities, and the peculiar color of the eggs and placentae, 

 which is darker or lighter purplish-black, or some similar shade (see 

 Ortmann, "17). 



Also here we have the phenomenon that flat and compressed 

 forms are found in the headwaters, swollen forms in the larger 

 rivers, with the intergrades between them in the rivers of medium 

 size. The transition is complete and very gradual, so that it is ex- 

 tremely difficult to draw separating lines. The division into three 

 local (or rather ecological) races, introduced here, is entirely arbi- 

 trary, but justified to a degree by the old division into " species," and 

 the fact that it is just such an intergrade which has first received a 

 name (bamesianns). The difficulty of classifying these forms be- 

 comes greater yet, because these shells vary not only in obesity, but 

 also in general outline, development of beaks, and color markings. 



I shall distinguish three forms: barnesiana bigbyensis, with the 

 diameter less than 40 per cent, of the length; barnesiana, with the 

 diameter from 40 to 49 per cent. ; and barnesiana tumescens, with 

 the diameter of 50 per cent, and over. 



9. Fusconaia barnesiana (Lea), 1838. 



Unio bamesianns Lea, '38. — Unio meredithi Lea, '58. — Unio pudicus 

 Lea, '60. — Unio lyoni Lea, '65. — Unio bamesianus and pudicus 

 Lewis, '71. — Unio tcllicocnsis Lea, 'y2. — Unio Icnticidaris Lea, 

 'y2. — Pleurobema barncsianuni, pudicujn, Icnticularc, meredithi 



