56 University of Michigan 



diameter are 60% and 40%, respectively). Thus the name 

 ma-stus Lea is the oldest available one. 



The later names given by Lea and claimed by Ortmann as 

 possible synonyms {cylindrellus and corvunculus) need not be 

 considered here. Their validity depends upon taxonomic con- 

 siderations, and these two forms require additional study 

 before their standing can be settled. 



Genus Conradilla Ortmann, 192 1 -' 



Type: Unio ccelatus Conrad. 



ConradiUa Ortmann, Naut., XXXIV, 1921, p. 90. 



CoxRADiLLA c^LATA (Conrad), 1834 



Type locality: Tennessee, Elk, and Flint rivers. j 



Unio {Lemiox) rvmosus Rafinesque, '31, p. 3. 

 Unio ccelatus Conrad, '34, p. 338, pi. i, f. 2; '34, p. 29, pi. 13, f. 4. 

 Micromya ccelata (Con.), Simpson, '14, p. 34. 

 Lemiox rimosus (Raf.) = U. ccelatus Con., Frierson, '14, p. 7. 

 Lemiox rimosus (Raf.), Ortmann, '16, p. 39; '18, p. 574. 

 Micromya ccelata (Con.), Walker, 'I8^ p. 4, i8c, p. 185 (new generic 

 name should be proposed). 



Frierson has identified U. rimosus with U. coelatiis chiefly 

 on the strength of the word "rimose" in the description, which 

 is intended to describe the sculpture of the shell. Walker 

 objects to this. Although this word may be taken as giving 

 a good description of this feature of the shell, other points in 

 the description do not fit. 



Rafinesque ('31, p. 4) makes the following explicit state- 

 ment of his theory of comparative measurements : "The com- 

 parative proportions of the length, breadth, diameter and axis 

 of the Unios and other bivalve shells having been misunder- 

 stood by some, it may be needful to state that my formula is 

 a kind of abbreviation of a longer exposition. Thus, when I 

 say, length one-half, diameter one-third, axis one-fourth of 

 the breadth, I meant to say and must be understood to state 



