{2 University of Michigan 
ognizable species (see below) and is congeneric with U. pli: 
catus Say, the type of Crenodonta Schlueter ’36, Amblema 
Raf. ’19, thus supersedes Crenodonta. 
AMBLEMA COSTATA Rafinesque, 1820 
Type locality: Ohio River and small rivers of Kentucky. 
Amblema costata Rafinesque, ’20, p. 315, pl. 82, figs. 13-14. 
Unio undulatus Barnes, ’23, p. 120, pl. 2, f. 2. 
U. costatus Rai.=U. undulatus Bar., Conrad, ’34, p. 68; Ferussac, 
735,".D. 272, Conrad, 736; p. .17- 
Quadrula undulata (Bar.), Simpson, ’14, p. 819. 
Quadrula costata (Raf.) =Q. undulata (Bar.), Vanatta, ’15, p. 556 
(“type” examined). 
Amblema costata Raf.—U. undulatus Bar., Frierson, ’16¢, p. 62. 
» D 
Amblema plicata costata (Raf.) =U. undulatus Bar., Utterback, ’16, 
p. 39; Ortmann, ’18, p. 538. 
Quadrula undulata (Bar.) = A. costata Raf. or U. rariplicata Lam., 
"19, Walker, ’18¢, p. 170. 
There is unanimity among all authors that A. costata of 
Rafinesque is one of the “plicate’ forms of mussels. This is 
absolutely clear from the original description and figure, and 
most authors (all except Walker) have unhesitatingly identified 
it with U. wndulatus Bar. of authors. 
Rafinesque calls his species in the description “applati” 
(flattened or compressed), and thus it is evident that we 
should refer costata to that form of the plicata group (genus 
Amblema) which differs from the others in the first place by 
its compressed shell, and this is the shell commonly called 
undulatus Bar. 
Thus, A. costata is identifiable from the original description, 
which in addition has been verified by Vanatta by the exam- 
ination of the so-called Rafinesque-Poulson type. The name 
is valid. 
As to undulatus Bar., see under Megalonaias gigantea Bar. 
