88 PALjEONTOLOGY OF NEW YORK. 



foramen on one of the valves. The New York specimens have, however, not 

 proved so satislactorilj preserved as those of the same species from the Black 

 shale of Kentucky, and from a study of the latter, Mr. Ulrich has determined 

 the generic relations of this interesting fossil to be quite distinct from what 

 had been previously assumed. By the favor of Mr. Charles Schuchert we have 

 had the opportunity of studying Mr. Ulrich's type-specimens, and, in addition 

 to these, have had access to a considerable number of specimens from the Gen- 

 esee slate of New York. Though compelled to differ in some respects from 

 Mr. Ulrich's diagnosis of this I'ossil, our observations agree with his in most 

 essential points. The muscular impressions and fulcra are so faintly defined, 

 even on the best preserved specimens, that allowance may readily be made for 

 personal differences of observation ; for this reason, however, extreme care has 

 been taken to ascertain the permanent, and eliminate the fugitive characters 

 of this, the only species known to represent the genus. 



In the pedicle-valve the groove or slit is very short, sometimes appearing as 

 a mere notch in the posterior margin, but, when well retained, comes to an 

 acute termination at a point about one-tenth the distance across the valve. 

 When the valve is uncompressed, this slit lies wholly on the posterior subapical 

 slope. 



On the interior of this valve a faint ridge is continued forward from the 

 proximal end of the slit, extending to a point about one-third the distance 

 across the valve. This is flanked on each side by a low muscular callosity 

 which narrows anteriorly and leaves the septum projecting on the median line. 

 The margin of this callosity is grooved by distinct muscular impressions, and 

 the groove extends about the anterior edge of the septum. 



The scars abutting against this callosity may be termed the centrals, and they 

 have essentially the same character as in the genus Obolella. From the post- 

 lateral margins of the callosity extend narrow curved lateral scars, reaching 

 to, or beyond the center of the valve, and though not always discernible they 

 appear with great distinctness on the best preserved specimens. At the posi- 

 tion of the cardinal scars as seen in Obolella, are sometimes depressions in the 

 shell that may indicate the point of attachment of such muscles. 



