liv SYNOPSIS OF GENERA. 
Clinopistha, Meek and Worthen (Proc. Acad. Nat. Sci., Phila., p. 43. 1870). 
Dystactella, Hall and Whitfield (Twenty-fourth Ann. Rep. 
N. Y. State Museum Nat. Hist., p. 192. 1872). 
Compare Solemya, Lamarck. 1818. 
[Type, Clinopistha antiqua, Meek.] 
Shell equivalve, inequilateral, transversely sub-elliptical, obliquely truncate 
in front, with a callosity or fold occupying the place of the lunule. Beaks 
small, situated anterior to the middle. Anterior end oblique, often nasute 
below. There is usually a broad shallow cincture extending from the beaks to 
the base, sometimes constricting the margin. 
Test thin. Surface, in the known species, marked by concentric strise of 
growth. Internal characters not satisfactorily determined. Several specimens 
have shown some indications of crenulations along the hinge, but this appear¬ 
ance may be due to the crystallization, and subsequent partial solution, of the 
margin of the shell. Ligament external. Muscular impressions of moderate 
size, distinctly marked, situated near the margins of the valve. Pallial line 
entire, composed of a series of radiating pustules as seen on the cast. 
The species formerly referred to Dystactella appear, on further examination, 
to be congeneric with Clinopistha , and it would seem that this latter genus does 
not differ exteriorly from Solemya , except in the oblique anterior end and absence 
of radii. 
The type species has many points of resemblance to the species which was 
made the type of Dystactella ( D. subnasuta), and further collections may prove 
their identity. 
Example: Clinopistha subnasuta , pi. li, figs. 32, 33; pi. xcv, fig. 31. 
Modiella, Hall (Pal. N. Y., vol. v, pt. 1. Plates and Explanations: 
PI. lxxvii, figs. 9-20. 1883). 
[Type, Modiella pygmcea, Conrad, sp.] 
Shell equivalve, very inequilateral, obovate. Anterior end short. Posterior 
end very broad and curved, or obliquely sub-truncate at the extremity. Beaks 
anterior. Cardinal line arcuate. Umbonal region prominent above, merging 
into the general convexity below. 
