EARLY DEVONIC HISTORY OF NEW YORK AND EASTERN NORTH AMERICA 2g 



less complete specimen in which the left valve is impressed upon the right 

 shows that the surface of the latter was crossed by very strong radial and 

 very distant ribs, the broad flat interspaces sometimes carrying intercalating 

 ribs of lower order. These were crossed by co'ncentric lines, presumably 

 lamellae. The aspect of the surface is thus not unlike that of P . inter- 

 cos tat a but the outline is very different and the right valve is distinctly 

 ribbed. The species P. brisa from Chapman Plantation [see p. 104], the 

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



Photo, by Charles Schuchert 



Iiitrusives at Stewart's cove, Dalhousie, with interbedded sediments 



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. 

 Horizon. Nos. 8, 9. 



Pteronitella hirundo Clarke 



Plate 4, figures 8-n 



Pteronitella hirundo Clarke. N. Y. State Mus. Bui. 107 1907. p. 211 



Shell much elongate on the hinge, terminating posteriorly in a slender, 

 acute point, anteriorly blunt, the auricle atrophied and the anterior slope of 



