MIOCENE MOLLUSCA AND CRUSTACEA. 41 
Mr. F. B. Meek, in his revision of the genus Barbatia,' further describes 
and characterizes the genus as follows: ‘Shell transversely oblong-ovate, 
with rounded extremities and a deeply sinuous basal margin; surface radi- 
ately striate; area moderate; cartilage furrows very small, crowded, and 
crossing the area at right angles to the cardinal margin; hinge rather dis- 
tinctly arched, with denticles hollow.” 
There have been so many generic divisions of this group of shells that 
it has become extremely difficult to say to which of several any certain 
form must properly belong, and in the present instance it is somewhat difti- 
cult to say wherein the present genus differs from some others; particularly 
Breviarca of the same author, except in the hollow teeth-like denticles, 
Mr. Meek ranges Striarca as a section under Barbatia of Gray, and Mr. 
Tryon ranges Breviarea as a section under Lamarck’s genus Cuculleea; on 
what grounds, however, they are to be so separated I do not quite see, as 
Striarca centenaria, the typical species, has the muscular impressions elevated 
and margined to a much greater extent than any Breviarea I have ever 
seen. In general form, perhaps, there may be some more reason for the sep- 
aration than in the internal structure, as in the present genus the body of 
the shell is suleated along the middle, but as Conrad states its basal margin 
is “closed,” not having a “small gape,” as Mr. Tryon supposes, while that 
of Breviarea is full and rounded. Still, I do not think this ought to be con- 
sidered as of generic importance. Perhaps the hollow teeth in this case 
might safely be taken as of generic importance, but so far as I know it is a 
species by itself yet, no other one having been recognized as possessing this 
peculiarity. So far, however, it would only be a specific feature, and no 
general feature distinguishing the two can readily be found. 
‘Invert. Paleont., vol, 9, U.S. Geol. Surv. of the Terr., p. 78. 
