Maryland Geological Survey 369 



Beak prominent, pointed, in some forms straight, but in most forms 

 slightly incurved over that of the dorsal valve. Dorsal valve much more 

 convex than the ventral valve, abruptly deflected in front and towards 

 the lateral margins ; beak incurved beneath that of the ventral valve. Sur- 

 face marked by thirty or more low, simple, rounded plications, which 

 become indistinct and are almost obsolete near the beak and are faint near 

 the lateral margins. The lateral margins are slightly inflected so that the 

 sides become distinctly concave. Fold and sinus very faint or absent 

 entirely. The anterior portion is rounded. The plications and depressions 

 interlock to produce sharply serrated lateral and front margins of contact. 

 Dimensions of an average individual : 18 mm. long, and 15.5 mm. wide. 



This form most closely resembles Uncinultis campbellanus of the 

 Helderberg. In the latter species the dorsal valve is elevated near the 

 front into a broad undefined mesial fold, the ventral valve is compressed 

 and a broad sinus occupies the entire width of the narrow front, the front 

 margin curves upward and extends into a subtriangular prolongation. 



In Uncinulus convexorus the dorsal valve is not elevated near the front 

 and there is no distinct mesial fold; the ventral valve is plano-convex. 

 There is an undefined sinus in some individuals while most individuals 

 have no sinus, and the front margin is rounded and sharply serrated. On 

 account of the characteristic rounded margins the name Uncinulus coih- 

 vexorus has been applied to it. 



Occurrence. — Helderberg Formation, Keyser Member. Tonoloway, 

 Cash Valley, Viaduct Cumberland, Cookerly, Pinto, Maryland; near 

 Cheriy Eun, Keyser, West Virginia ; Hyndman, Pennsylvania. 



Collections. — Maryland Geological Survey, U. S. National Museum. 



[Maynard.] 



Genus WILSON I A Kayser 



WiLSONiA GLOBOSA Wcller 



Plate LXV, Figs. 15-17 



Wilsonia globosa Weller, 1903, GeoL Survey N. J., Pal., voL iii, p. 235, pi. xxi, 

 figs. 12-22. 



Description. — " Shell subglobose, a little longer than wide. Pedicle 

 valve less convex than the brachial, its beak suberect or slightly arched, 

 acutely pointed, umbo smooth and convex, mesial sinus shallow, beginning 

 24 



