NODULARIA 959 
a little to one side; pseudocardinals broken up into several 
slightly curved, subradial denticles; anterior scars deep and 
large. 
Length 155, height 45, diam. 38 mm. 
China. 
Unio grayanus SCHRENCK, Reis und Forsch. in Amur-Lande, 
1867, p. 694, pl. xxvul, figs. 1-3. 
Nodularia cylindrica Stmpson, Pr. Ac. Nat. Sci. Phila., 1900, 
p. 84; Syn., 1900, p. 807. 
Lanceolaria cylindrica Haas, Con. Cab., Unio, 1910, p. 58, 
pl. 5, figs. 1-3. 
Schrenck supposes this species to be the Unio grayanus of 
Lea, but it is very different. There is no pinched up or ele- 
vated posterior ridge whatever as there is in that and all the 
species 1 have placed with it. It is an almost cylindrical, 
smooth shell, with very thick, apparently silky, epidermis. The 
line of junction between the valves behind is wavy and the 
hinder part of the shell is turned to one side a little, as is the 
case in N. gladiolus. 
Section NODULARIA S. S. 
Characters the same as the genus. 
Group of NV. douglasie. 
Shell olive to blackish, subsolid : surface more or less covered 
with nodules arranged in subradiating or chevron-shaped pat- 
terns. 
NoODULARIA DOUGLASL® (Gray). 
Shell somewhat elongated, subsolid, subinflated, inequilat- 
eral: beaks full, with nodular, zigzag-radial sculpture ; anterior 
end rounded; base line straight or slightly incurved in the 
middle, full behind; posterior ridge moderate, ending in a 
point about at the median line; surface in the umbonal region 
sculptured with nodulous chevron-shaped or irregular corru- 
gations, the remainder of the shell usually smooth; epidermis 
