42 NAIADES OF MISSOURI 
morphologically and less liable to parallelism and convergence. 
We should not, however, lose cognizance of the importance con- 
cerning shell characters. External factors may so shape the 
shell, as to individualize it, but, under normal conditions, do not 
often, destroy all traces of indentification with some group. Since 
validity is so dependent upon the examination of both hard and 
soft structures of large series of individuals, it is felt that the 
species, as recorded for their extensive and intensive studies 
herein, are fairly well settled within their genera. Fortunately 
extensive field work has made this intensive study possible. On 
one occasion the rare opportunity was given the author to make 
a mussel survey of three hundred miles down the Osage River 
in a row boat and ample time was given to the study of one of the 
richest faunae of Missouri. Two papers, ‘“‘ Mussel Studies Afield’’. 
for the years 1913 and 1914, are now in MS. recorded matter of 
which is submitted herewith. ‘The ecologic facts secured in these 
field surveys are especially interesting. For example, in the long 
trip down the Osage, the largest tributary of the Missouri in the 
interior of this state, it was found that the flat or compressed 
forms found at the headwaters, where the water is shallower 
and swifter, become more swollen and heavier shells further down 
stream where the water is deeper and more sluggish. The most 
valuable data gathered from these field excursions are the ecologic 
as illustrated in Plates x—xiv. Much physiologic and mor- 
phologic information, however, has been obtained from these 
immediate studies in nature that could not be secured otherwise, 
since actual observation have been made of the animal carrying 
on the nutritive and reproductive functions there as well as 
observed through aquarium studies (See Plate ix). More accurate 
idea of the morphology (especially of soft. parts as to color, form, 
etc.) is obtained while the specimens are fresh and uncontracted as 
examined afield. 
While this catalogued account is rather synoptical as to the 
text of its animal and shell characters, yet it has been the effort 
to be more complete than those literary works of somewhat 
similar character that have devoted more space to the structures 
of the shell; hence, much description will be found to be completely 
given for the first time, notably those of M. heros (Say), 
QO. quadrula (Raf.) P. Utterbackit Frierson, R. tuberculata (Raf.), 
U. tetralasma (Say), Las. suborbiculata (Say), Prop. capax (Green), 
