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THE NAIADES OF MISSOURI 265 
it becomes thicker and more compressed and more elongated. 
Its changes are so great at different ages that many names have 
given it for this reason; doubtless A. opaca, stewartiana, leonensts, 
elc., are mere synonyms for this reason. Because of parasitism, 
pounding of the surf, etc., this species is found in many pathologic 
forms in our lakes; a common one being that of a shell deeply 
suleated at the post-ventral point and another with its shell 
extremely truncated post-dorsad. To the latter A. footiana and 
perhaps A.dakotana, may be referred. A.salmonia may also be 
assigned to a grandis-form that has a blistered salmon-colored 
nacre due to a distomid infection. A. grandis has a general distri- 
bution all over the Mississippi drainage, also in the St. Lawrence 
drainage and that of the Red River of the North. In this State it 
is found in most of its forms in the chain of lakes, ‘‘cutoffs,”’ 
sloughs and bayous along the Missouri River and quiet, muddy 
creeks of the north and central portions. It has only been rarely 
reported for the Ozark Center or Plateau. The soft parts of the 
half-grown grandis (A. opaca) are found by Domestic Science 
tests to be very edible. A strict breeding record, kept by the author, 
shows this species to be gravid with glochidia from December 
until March and sterile from this month on to September; there- 
fore it is a long period breeder and its larvae are the largest and 
most active known, contracting from ten to fifteen times per 
minute. The species which follow in description under this genus 
are only believed to be as mere forms of grandis and only receive 
separate notice because of their original report for this state, 
under these names,—and are so grouped for sake of conformity 
to other writers. 
Anodonta dakotana Frierson. 
(‘Dakota Shell,’’ ‘““Short Nose.’’) 
Pl. XXIV, Bigs, 772A and’ B. 
1914—Anodonta dakota Frierson MS. 
ANIMAL CHARACTERS:—With the exception of shorter, wider 
gills, due to the shape of shell, the nutritive and reproductive 
structures of this species/(if it be one) are identical with those of 
A. grandis. Its marsupium, in gravidity, is exactly the same; 
so are its glochidia in form and size (0.400 x 0.395mm.). 
SHELL CHARACTERS:—Shell subrhomboidal, short, obese, 
abruptly truncated behind and, with the exception of not being 
