NAIADES OF MISSOURI : 137 
Missouri approach more the typical guadrula in being more com- 
pressed and more tuberculated. Perhaps the most typical guadrula 
of Missouri is.to be found in the geographic center of the state 
where the flatter, thinner and more “‘lachrymosed”’ shell occurs. 
As in many of the species of these related genera the intergrades 
are so numerous that we can consider only the most striking ones 
that may be traced to mere local conditions. The author has 
found this species to be the most sensitive to discharge its conglu- 
tinates immaturely when disturbed from its natural bed and then, 
too, since conglutinates, spawned in nature, have been examined 
to find them containing late embryos it is to be inferred that 
maturity may take place outside. Hence we may account for 
our difficulty in securing the mature glochidia from the ovisacs 
of the mother. he writer has examined hundreds of gravid 
quadrula in mid- and late summer only to find every stage of 
embryonic development except the glochidial. In this respect 
this species resembles Q. verrucosa and the fact that the ovisacs 
of each contain unusually large quantities of mucus may have 
some association with their eccentric breeding habits. The breed- 
ing season of Q. quadrula is from May to August and hence is 
tacytictic. 
Special attention 1s given here to a deeply sulcated form of this 
species which occurs rather commonly in our North West Missouri 
lakes but which may only be a pathologic condition due perhaps, 
to parasitic attacks upon the mantle glands that build up the 
shell. Three type shells measure as follows: 
Sex Length Height Diameter Um. ra. Locality 
UO hn Xe 7 Ol) Xi gem 0.485 (Lake Contrary, St. Joseph, Mo.) 
fe) 80 X 55 x 54 ” 0.450 ( ” ” ” ” ” ) 
” ” 9” ” x” ” ) 
48) xX. 38" x 40 0.435 ( 
These measurements show an unusual inflation and extra- 
ordinary position of the umbones. If this should be a normal 
form it would deserve specific consideration because of the deep 
post-dorsal sulcation and also because of the wide, deep radial 
furrow in front of the prominently angled post-umbonal ridge. 
However, since Mr. Frierson concurs with the author in the belief 
that it may only be ‘a strange freak” after all it would be dismissed 
here with only the reference to its photograph (Pl. XVIII, Figs. 
46 A and B.) 
