Uv SYNOPSIS OF GENERA. 



Clinopistha, Meek and Worthen (Proc. Acad. Nat. Sci., Phila., p. 43. 1870). 



Dystadella, Hall and Whitfield (Twenty-fourth Ann. Rep. 



N. Y. St4ite 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 striae 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 tlie 

 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 Dystadella appear, on further examination, 

 to be congeneric with Clinopistha, and it would seem that this latter genus does 

 not tliffer 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 Dystadella {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. Ixxvii, figs. 9-20. 1883). 



[Type, Modiella pygmaea, 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. 



