256 NEW YORK STATE MUSEUM 



placed about 1.5mm apart on the main part of the shell but crowded 



as they curve around the anterior ear. The posterior ear is not 



preserved but was apparently much larger than the anterior one. 



On the ventral part of the shell the primary ribs increase in width 



anteroposteriorly from re to -h inch while the grooves increase but 



slightly in .breadth. 



P.? naviformis (Conrad) 



One well preserved left valve from the Coeymans has all the 



characteristics of this species. Hall cites it from the Pentamerus 



limestone, whether lower or upper he does not say.^ 



Megambonia aviculoidea Hall 



Owing to the coarsely crystalline character of these shells, they 

 are seldom sufficiently well preserved to admit of identification for 

 the rock on breaking fractures more easily through than around 

 them. It is apparently quite abundant in the Upper Manlius. 



Actinopteria communis (Hall) 

 The specimens identified with this species have rounded radiating 

 ribs and are not nodose. One quite well preserved specimen was j 

 found in the Lower New Scotland. 



A. textilis (Hall) 

 A^ery abundant in the Lower Oriskany. The surface has strong 

 radiating ribs which at the base are distant from one another about 

 three times their width. In the middle of each intermediate space 

 is a finer radiating ray. Concentric ridges give a cancelated appear- 

 ance to the entire surface. The large specimens from here are of a 

 size similar to those termed small by Professor Hall.^ A compara- 

 tively large specimen was 30mm long from tip to tip of ears and 

 32mm in greatest length from the hinge to the front of the shell. 



A. textilis var. arenaria (Hall) 

 This differs from the above merely in having the concentric ridges 

 accentuated, becoming imbricating lamellae and spinose where they 



^See Conrad. Acad. Nat. Sci. Jour. 1842. 8:210, pl.i, for original descrip- 

 tion. 

 Tal. N. Y. 3:288, pi. 53, fig.2-io. 



i 



