138 THE AMERICAN MIDLAND NATURALIST 
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, inclined 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 
Oo 73.5 X 64.5 xX 44.0mm 0.495 (Lake Contrary, St. Joseph, Mo.) 
OF76.0. X* 06,01 45.0) 2. O500) AC Pit ss 2) 3 ae) 
Gi 1.64.0 xX 7010) X" 50.0). adsanicid. i: Py ses ota) 
ORATION ks OLON BL On es OW ZO ese 2} pe San) 
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, 
