0RISKANY FAUNA OP BECRAFT MOUNTAIN 33 



complete, the casts generally showing obscure nodes on the radii where 

 these have been crossed. 



Prof. Hall describes as A v i c u 1 a recticosta a single right 

 valve from the Oriskany sandstone of Albany county, characterized by 

 its strong ribs, which are said to proceed in pairs from the umbo and 

 to dichotomize; in these respects that shell is unlike those with which 

 we are here dealing. 



This is the most abundant of the larnellibranchs of this fauna. In 



its general features it may be brought into comparison with several of 



the Ulsterian and Hamilton species, but its specific traits are distinct 



and pronounced. 



Pterinopecten signatus, sp. nov. 



Plate 4, flg. 3 



Shell of medium size, obliquely suboval. Hinge-line straight and 

 long, not exceeding the greatest diameter of the valves. Anterior ear 

 strongly developed and nasute; posterior of moderate size not sharply 

 set off from the body of the shell. On the left valve the byssal 

 depression is strong, the surface normally convex. The ornament of 

 this valve consists of narrow, filiform subequidistant radii, increasing 

 by implantation, the first of the minor series generally attaining on the 

 margin the full size of the primary series. The interspaces are broad, 

 free and subequal on the margins. These radii cross both wings, but 

 are obscure on the anterior. Fine, erect concentric lines cross all radial 

 lines; toward the edges these become crowded, lamellose and overlap 

 each other. The right valve is depressed convex or flattened and bears 

 radial striae, but the concentric lines are obscure or wanting except on 

 the wings. 



This rare species is readily distinguished from Pt. proteus by 

 its fine, regular and uniform radii. It resembles the Onondaga species 

 Pt. terminalis, but not closely. Pterinopecten bellulus 

 of the Helderbergian is unlike it in having dichotomous and fascicu- 

 late radii. 



Pterinopecten pumilus, sp. nov. 



Plate 4, flg. 



The sole example observed of this species is a right valve of very 



