2IO NEW YORK STATE MUSEUM 



times carrying intercalating ribs of lower order. These were 

 crossed by concentric lines, presumably lamellae. The aspect of 

 the surface is thus not unlike that of P. intercostata but the 

 outline is very different and the right valve is distinctly ribbed. 

 The species P. b r i s a from Chapman Plantation, the descrip- 

 tion of which is based on a right valve, is a very close approach to 

 this in respect to outline and surface characters, though a more 

 •elongate, erect shell. To express this intimate relation the present 

 form is regarded as a variety of the latter. 

 Lower Devonic. Dalhousie, N. B. 



Pterinea (Pteronitella?) incurvata n 



ov 



Valves elongate on the hinge, the greatest length of the hinge 

 "being almost twice the hight of the shell. Anterior wing well 

 defined on both valves, byssal sinus not deep but broad and not 

 marked by a notch on the right valve. Beaks one third the length 

 of the hinge from the anterior extremity. General outline very 

 oblique. Left valve highly convex and incurved over the body, 

 sloping abruptly to the posterior wing, more gradually to the 



Pterinea (Pteronitella?) incurvata 



broad byssal sinus in front. From the prominent umbo the cres- 

 cence line swings in a curve backward and forms a strong pro- 

 jection on the lower margin. The posterior wing is extended well 

 beyond the posterior margin of the body and bounded by a con- 

 cave curve which terminates in . an acute point. Its surface is 

 depressed in a direction conforming with the curve of the body. 

 The surface of this valve is covered with regular concentric growth 

 lines which are essentially unmodified on the anterior and posterior 

 wings but the body of the valve bears radial striae which have 



