Makylaxd Geological Si-rvey 569 



centric shell lamina^ and shows the flattened cardinal slopes, two features 

 which serve to distinguish the species. The ventral valve bears the 

 rounded radial stria?, sparsely spinous. The reference of this species to 

 the subgenus Marginifera was based upon the development of granulosa 

 divergent ridges on the interior of both valves making a sharp division 

 between the cardinal shoulders and the general interior cavity of the 

 shell; an inceptive condition in relation to the fully developed differentials 

 of the Carboniferous and Permian Margin ifera. 



Occurrence. — Jennings Formation, Cheaiung Member. Oakland- 

 Altamont linad; Gordon's farm, 1 mile northeast jfountain Lake Park; 

 road over Trout Eun, 2 miles south of Oakland. 



Collection. — Maryland Geological Survey. 



Family ORTHIDAE 



Genus DALMANELLA Hall and Clarke 



DaLAIANELLA TIOGA (Hall) 



Plate LIT, Figs. 1-4 



Orthis interlineata Hall (non Sowerly), 1843, Geol. N. Y., Rept. 4th Dist., 



p. 267, flgs. 3, 4. 

 Orthis tioga Hall, 1867, Pal. of N. Y., vol. iv, p. .59, pi. viii, figs. 20-29. 

 Schizoplioria tioga Hall and Clarke, 1S92, Pal. of N. Y., vol. viii, pt. i, pp. 



212, 226, pi. vi, flgs. 17, 18. 

 Balmanella tioga Williams, 1908, Proc. U. S. Nat. Mus., vol. xxxiv, p. .5.5, 



pi. iii, figs. 1-7, 9, 10, 12. 

 Schizoplioria tioga Grabau and Shinier, 1909, N. Amer. Index Foss., vol. i, 



p. 268, fig. 321. 



Description.- — "Shell transverse, broadly elliptical, about two-thirds 

 as long as wide; length of hinge-line a little greater than half the width 

 of the shell; the extremities rounded into a general curved outline. 

 Dorsal valve convex, the grcntr'^t elevation near or above the middle on 

 each side of a well-marked mesial sinus ; sometimes a little flattened at the 

 sides, and regularly curving to tlie front. Ventral valve very gently 

 conve.v, with sometimes a slight mesial elevation; area of medium width, 

 with the beak slightly incurved; foramen wide. 



