^ 56 NAIADES OF MISSOURI 



Quadrula quadrula contraryensis Utterback. 



(Round Maple Leaf.) 



PL XVIII, Fig's 47 A and B. 



ANIMAL CHARACTERS. 



Nutritive Structures: — Same as that of the parent species, 

 except for an absence of a supra-anal opening, a difference in 

 the greater posterior extension of foot and also a general dif- 

 ference of form of soft parts due to a more rounded shape of 

 shell. 



Reproductive Structures: — Identical with that of the 

 parent species except for shorter, wider marsupia. 



shell characters. 



External Structures: — Shell medium in size, suborbiculate, 

 abruptly curved before, broadly rounded behind with very slight 

 incurvature post-ventrad; well inflated, incHned to globosity; 

 beaks full, high up on dorsal line (as indicated by the large average 

 umboidal ratio of 0.495) ; tubercles few and small, mostly on 

 umbonal area; post-umbonal ridge rounded, scarcely sculptured; 

 sculpturing on beaks corrugated as on parent species; epidermis 

 olivaceous. 



Internal Structures: — Cardinals different from parent in 

 being reduced to a single, jagged tooth in right valve; somewhat 

 double in left; interdentum long, wide, not so deeply gashed in 

 right valve for the reception of the post-right cardinal; umbonal 

 cavity deep, basin-like; nacre an unblemished white. 

 Sex Length Height Diameter Um. ra. Locality 



O^ 73-5 X 64.5 X 44.0mm 0.495 (Lake Contrary, St. Joseph, Mo.) 

 9 76.0 X 66.0 X 45.0 " 0.500 ( " " " " " ) 



cf 84.0 X 70.0 X 59.0 " 0.483 ( " " " " " ) 



9 41.0 X 36.0 X 38.0 " 0.520 ( " ' " " " " ) 



The young shell of the last measurement shows an approach 

 to the parent shell. The comparatively deep sulcation at the 

 post-ventral portion of the shell disappears as seen in a shell 

 series of fairly close connection in ages. 



Miscellaneous Remarks: — The author of this sub-species 

 is satisfied that he has a sufficient collection of this peculiar shell 

 taken from different parts of Lake Contrary, St. Joseph, Missouri, 

 to prove the validity of this form as a variety of that very common, 



