6O4 UNIO 
lapidosus in the New Edition of Rossmassler do not agree 
with the several speciments of discus I have examined, and 
the latter is somewhat more compressed than the measurements 
given for lapidosus, yet I feel sure that von Martens is right. 
The U. lapidosus differs totally from any form found in the 
Paleerctic region or for' that matter in the Old World, and 
I felt a good deal of doubt concerning this remarkable in- 
truder into the circummediterranean region. But I confess 
that it had not occurred to me that it might be U. discus until 
I read von Martens’ statement. 
Group of Unio sloatianus. 
Shell rhomboid, solid, inflated, with a well-defined posterior 
ridge and a smaller, fainter one above, making the posterior 
of the shell distinctly biangulate, nearly straight or slightly 
incurved on the base, rounded in front ; beaks only slightly ele- 
vated ; beak sculpture not observed; surface of the valves cov- 
ered with somewhat radiately plicate, nodulous corrugations, 
which become less pronounced in front; posterior slope radi- 
ally plicate; epidermis dark; pseudocardinals stumpy, radial, 
granularly striate; laterals double in the left valve, single in 
the right, with a faint, secondary ridge below ; anterior muscle 
scars deep, nearly smooth ; cavity of the beaks moderate, slight- 
ly compressed. 
Animal unknown. 
UNIO SLOATIANUS (l,ea). 
Shell subrhomboid, somewhat inflated, solid, inequilateral, 
apparently with rather full, elevated beaks; posterior ridge 
high, angled, becoming double midway down, and ending at 
the posterior basal part of the shell in a biangulation ; anterior 
end a little narrowed and rounded; base line straight; poste- 
rior slope obliquely truncated ;surface mostly covered with sub- 
radiating, corrugated ridges. Those on the disk are almost 
vertical and show a tendency to break into nodules; those on 
the posterior ridge and dorsal slope are Strong and almost 
