290 Systematic Paleontology 



The zoarium is ramose and bifoliate, consisting ef freqi;ently bifurcat- 

 ing branches varying in width from 2 to 2^ mm. Zocecial apertures are 

 circular with well-marked peristomes about .25 mm. in diameter, ar- 

 ranged in indistinct, longitudinal rows. 



Occurrence. — Helderberg Formation, New Scotland Member. 

 Kreigbaum. 



Collection. — Maryland Geological Survey. 



Class BRACHIOPODA^ 



Order NEOTREMATA 



Superfamily DISCINACEA 

 Family DISCINIDAE 



Genus ORBICULOIDEA d'Orbigny 



Orbiculoidea roederi n. sp. 

 Plate LIII, Figs; 1,2 



Description. — Shell large and nearly circular in outline. Dorsal valve 

 tumid, with the obtuse apex situated from one-third to one-fourth the 

 length of the shell from the posterior region; surface uniformly convex 

 except back of the apex, where it is steep and slightly convex or concave. 

 Ventral valve somewhat convex except in front of the apex, where it is 

 more or less concave; pedicle sinus large, deep, and long, beginning a 

 little in front of the center and extending to near the posterior margin. 



Surface of both valves marked by sharply elevated, high, flattened con- 

 centric ridges separated by concave spaces about three times as wide as 

 the ridges. About six ridges in 3 mm. near the posterior edge of the 

 ventral valve. 



The relations of this species are with 0. aiiipJa, the only other large 

 form of the Oriskany. The latter, however, is larger, with the dorsal 

 apex subcentral, and with much stronger and more distant concentric 



' This section is by Charles Schuchert except where other contributors are 

 indicated. 



