114 THE NAIADES OF MISSOURI 



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, leonensis, 

 etc., 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 

 sulcated at the post-ventral point and another with its shell 

 extremely truncated post-dorsad. To the latter A. jootiana and 

 perhaps A. dakotana, maybe referred. A.salmonia may also be 

 assigned to a grandis-jorm 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 vState 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 conformit}^ 

 to other writers. 



Anodonta dakotana Frierson. 

 ("Dakota Shell," "Short Nose.") 

 PI. XXIV, Figs. 77 A and B. 

 191 4 — 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 



