26 The Fauna of the Keyser ]\Iember of the 



account of the characteristic rounded margins the name Uncinulus con- 

 vexorus has been aiDplied. to it. 



Occurrence. — Helderberg Formation, Keyser Member. Tonoloway, 

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

 Cherry Eun, Keyser, ^Vest Virginia ; Hyndman, Pennsylvania. 



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



Genus WILSON I A Kayser 



WiLSONiA GLOBOSA Wellcr 



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 

 near the middle of the valve and produced as a lingual extension in front, 

 at nearly a right angle to the plane of the valve. Brachial valve strongly 

 convex or gibbous, smooth posteriorly, anterior margin deeply sinuate, 

 mesial fold slightly elevated, originating near the middle of the valve. 

 The surface of each valve is marked by sixteen or eighteen simple, low, 

 rounded plications, sometimes slightly grooved anteriorly and becoming 

 nearly or quite obsolete posteriorly, leaving that portion of both valves 

 smooth. From two to five plications are included within the sinus, the 

 more common number being four, with a corresponding number in the 

 fold of the opposite valve. The dimensions of a rather large globose in- 

 dividual are: Length 12 mm.; width 11 mm.; thickness 10 mm. Those 

 of another less globose specimen are: Length 11.25 mm.; width 10.5 

 mm. ; thickness 7.5 mm. 



" In some of its characters this species resembles the Helderbergian 

 forms Uncinulus mutabilis Hall and U. nucleolatus Hall. It differs from 

 both of them, however, in its smaller size, and in the obsolescence of its 

 plications on the posterior portions of the shell. Internally there are 

 conspicuous differences which are of even generic value. In Wilsonia 

 glohosa the cardinal process is absent, the hinge-plate is divided and is 



