EARLY DEVONIC HISTORY OF NEW YORK AND EASTERN NORTH AMERICA IO5 



Pteronitella peninsulae Clarke 



Plate 25, figures 8, 9 



Pteroni tella p enins u lae Clarke. N. Y. State Mus. Bui. 107. 1907. p. 212 



Very sharp internal casts of right valves show the characteristic struc- 

 ture of this genus as defined by Billings, clearly demonstrating the departure 

 from the type of Pteronites in the presence of a series of Cyrtodontalike 

 teeth beneath the beak, together with the long posterior ridgelike tooth. 

 These valves are very oblique, the straight hinge making the greatest 

 diameter of the shell ; the anterior wing is insignificant and the posterior 

 not extended. From anterior and posterior cardinal angles the lateral 

 margins depart at almost 90 degrees. The beak is very near the anterior 

 extremity and the shell is quite convex along the oblique and somewhat 

 curved crescence line, from which the anterior slope is abrupt and the pos- 

 terior abrupt and slightly concave, at first becoming flat at the hinge. The 

 anterior scar is small and deep, the posterior large and faint. Beneath 

 the beak are three or four teeth diverging from the edge of the ligament 

 area. 



Locality. Presque Isle stream. 



Pterinopecten aroostooki Clarke 



Plate 24, figures 25-28 



Pterinopecten aroostooki Clarke. N. Y. State Mus. Bui. 107. 1907. p.i99 



Shells subcircular or somewhat transverse with outline slightly extended 

 posteriorly ; beak at the anterior third of the hinge, posterior hinge straight, 

 reaching to the extreme limit of the outline, posterior wing very slightly 

 extended ; anterior hinge straight, anterior wing moderately large but 

 undulated, an oblique ridge traversing it from the beak just beneath the 

 hinge leaving the portion behind it depressed and flat. Below this ridge 

 the ear is depressed or broadly sulcate. Umbo convex, narrow ; pallial 

 region sloping evenly downward and depressed. The surface sculpture 

 consists of well defined ribs, which are broad and sparse over the median 

 region where they usually carry one very small rib between each two of the 

 large ones. On the anterior slope and wing these ribs are smaller and also 

 on the posterior slope and wing. Cancellating lamellae cross the posterior 

 wing and are visible in the sulci of all the posterior surface of the valve. 

 The left valves only are known. 



Locality. Edmunds Hill. 



