312 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxvni. 



and on a slightly flattened space adjoining the posterior margin. Dor- 

 sal valve a])out as convex as the ventral and with the apex marginal. 

 The interior of the valve shows two rounded depressions beneath the 

 umbo with a slight, narrow groove between them; a little in advance 

 the outlines of the central muscle scars occur; originally strong but 

 faintly indicated radiating lines occur toward the front. 



()])xerrat!(>n!<. — This shell was identihed as the dorsal valve of Kutor- 

 (jlna ring 111 (tt((. by Mr. Billings'^ and myself.* They were considered 

 as distorted, flattened shells. Better material shows them to represent 

 one of the simplest forms of brachiopod known; with the exception of 

 the rudimentary pedicle furrow and the area there is nothing more 

 than the gaping valve, a form near to Dr. Charles PI Beecher's ideal 

 Patei'iiia. 



The specific name is given in recognition of the excellent work Mr. 

 George Edson, of St. Albans, Vermont, is doing iu collecting the 

 Lower Paleozoic fossils of his region. 



Fonimtlon and locality. — Swanton shales, justabove Parker's quarry, 

 Georgia, associated with Olenellus fhoaip.wnl,, and also two miles east 

 of Swanton, Vermont. 



Genus DICELLOMUS Hall. 



DiceUomus Hall, Twenty-third Ann. Rep. N. Y. State Cab. Nat. Hist., p. 246. 

 Dicellomnx Hall and Clarke, Pal. New York, VHI, 1892, Pt. 1, p. 72. 

 DiceUomus Walcott, Mon. U. S. Geol. Survey, XXXII, 1899, Pt. 2, p. 446. 



Shell small; general form ovate to subsemicircular, biconvex, with 

 apices marginal. Surface of outer shell tinely punctate in all species 

 where it is preserved uninjured. Interior or middle lamellae marked 

 by radiating striaj and minute punctee; inner surface finely punctate. 

 The shell is thick in all the species now known, and is built up of a 

 thin, outer, scabrous layer, numerous inner layers or lamelke, and a 

 thin inner layer. Shell substance apparently calcareo-corneous. 



The interior of the ventral valve shows a short area with a median 

 pedicle groove; an elongate visceral area; well-marked main v^ascular 

 sinuses; large, composite scars where the posterior muscles, i. e., 

 transmedian and anterior laterals, were attached; and a short shelf or 

 embryo spondylium that extended into the valve from each side of the 

 pedicle groove. This plate corresponds to the dental plate in the 

 articulate brachiopods, and it has a thickness at the antero-lateral 

 margin that suggests a short tooth. 



The interior of the dorsal valve has a well-defined but very narrow 

 area in one species, J), polltus.^ that is hollowed out so as to form a 

 shallow groove on each side, apparently for the reception of the short 

 tooth of the ventral valve. No good posterior margins of the valve 



ffPal. Fos., I, p. 9. 



^-Tenth Ann. Rept. U. S. Geol. Survey, p. 609, pi. lxix, figs. 1, la-h. 



