I 

 NAIADES OF MISSOURI 73 



SHELL CHARACTERS. 



External Structures: — Shell orbicular, to egg-shape in 

 general outline, disk tuberculated and transversely nodulous 

 between beaks and ventral margin in front of post-umbonal ridge; 

 latter flattened, dorsal ridge low, faintly costated; beaks low, 

 well placed anteriorly; epidermis light-brown to yellowish, some- 

 what glossy. 



Internal Structures: — Cardinals tripartite in left valve, 

 rather single in right; interdentum broad, rather doubly gashed 

 in right valve; laterals double in left and single in right valve; 

 mantle line high up from ventral margin; nacre whitish, pinkish 

 (or even bluish) within the mantle line, usually lighter color on 

 extra-mantle line border. 



Sex Length Height Diameter Locality 



cf 60 X 55 X 32 (Gasconade R., Gascondy) 



9 77 X 62 X 41 (Osage R., Monegaw Springs) 



d^ 70 X 64 X 40 ( " " Warsaw) 



Miscellaneous Remarks : — As this state is out of geographic 

 range of t5^pical cooperianus it is natural that no real type may be 

 found in Missouri. However, the writer upon finding a few shells 

 of the tuber citlata (Raf.) type with white and pink nacre submitted 

 one of the latter to Mr. Walker for his consideration. His com- 

 ments are:-^"A very curious and interesting shell. It has the 

 shape of Quadrula tuberculata (Raf.) but the nacre of cooperiana 

 (Lea) and I should call it that, although out of range. I never 

 heard of tuberculata except with purple nacre." A white nacred shell 

 of the same form is considered by Prof. Clark as " rather plump, 

 approaching granijera" but that the nacre "suggests cooperiana." 

 Other Missouri collectors have commented upon this strange 

 departure of R. tuberculata and granijera from type. However, 

 if it may be proved that this difference of nacre-color is merely 

 a "fading out" due to chemical reaction of mineral water there 

 would be instead of a true cooperianus in this state a mere local 

 form of a Rotundaria. The real home of this species is in the 

 Tennessee-Cumberland system where Wilson and Clark (1914, 

 pp. 44 and 60) have found it as a summer breeder (a tachytictic 

 species). 



