220 



NEW YORK STATE MUSEUM 



from the margin of the shell, and fine, regular, uniform, con- 

 centric striae, together with the hinge structure characteristic 

 of the genus ; C y p r i c a r d e 1 1 a tenuistriata [fig. 169] , 

 a shell of subrectangular outline with a pronounced umbonal 



Fig. 178 Phacops rana 



Yig. 177 Homalonotus d e k a y i 



angulation and extremely fine, tenuous, concentric striae; 

 Actinopteria boydi [fig. 170], an oblique winged shell 

 with the wing not strongly defined, a marked anterior ear and 

 strong surface markings with concentric striae, which however 

 do not interrupt the radii; Nyassa a r gut a [fig. 171], a 

 modioloid shell with numerous small teeth beneath the beak, arcu- 



