370 Systematic Paleontology 



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

 at nearly a right angle to the j^lane 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, Avith 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 arc: 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. nudeolatus 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 

 supported by a strong median septum. These characters, when associated 

 with its external form, place it in the genus Wilsoiiia, while the two 

 Helderbergian species mentioned possess well-developed cardinal proc- 

 esses and the other characters which distinguish the genus Uncinulus." 

 Weller, 1903. 



It occurs in the upper Decker Ferry of Kew Jersey. 



Occurrence. — Helderberg Formation, Keyser Member. Cumber- 

 land, Cash Valley. 



Collection. — U. S. National Museum. 



[Maynard.] 

 Wilsonia cf. globosa Weller 

 Plate LXV, Figs. 18-20 



Description. — Shell transversely subelliptical to subpentagonal in out- 

 line, broader than long. Ventral valve convex, plano-convex to depressed 

 convex; beak extending beyond that of the brachial valve and slightly in- 



