400 CAMBRIAN BRACHIOPODA. 



The species is quite widely distributed. The type came from the thin-bedded limestones 

 in the Dunderberg shale, at the summit of the Cambrian in the Eureka district, Nevada. T. W. 

 Stanton found what appears to be the same species in sandy shales and sandstones at Glenwood 

 Springs, Colorado. A partly exfohated, somewhat distorted ventral ( ?) valve from an Upper 

 Cambrian limestone one mile south-southwest of Highgate Falls, Vermont, appears to be 

 identical with 0. msera. 



Formation and locality. — Passage beds between the Upper Cambrian and the Ordovician: (205) Siliceous 

 limestone on Roundtop Mountain, Eureka district [Hague, 1892, Atlas], Eureka County, Nevada. 



Upper Cambrian: (313j [Hall and Whitfield, 1877, pp. 205 and 206]) Limestone in the Eureka district; and (61) lime- 

 stones in the Dunderberg shale [Walcott, 1908f, p. 184], a little south of the Hamburg mine; both in the Eureka 

 district [Hague, 1892, Atlas], Em-eka County, Nevada. 



(360h) Sandy shales about 200 feet (61 m.) above the base of the section at Glenwood Springs; and (360i) Sand- 

 stone about 100 feet (30.5 m.) above the base of the section at Glenwood Springs; both in Garfield County, Colorado. 



Middle Cambrian : (58) shaly limestones in upper beds of Secret Canyon shale, east side of New York and Secret 

 canyons. Eureka County, Nevada. 



A specimen that is somewhat doubtfully referred to Obolus msera occurs at the following 

 locality : 



Upper Cambrian: (319c[) Limestone 1 mile (1.6 km.) south-southwest of Highgate Falls, Franklin County, 

 Vermont. 



Obolus matinalis (Hall) . 



Plate VIII, figures 1, la-k. 



Orbicula prima Owen, 1852, Rept. Geol. Survey Wisconsin, Iowa, and Minnesota, p. 583, PI. I b, figs. 13 and 16-19. 

 (Described as a new species.) 



Lingulepis pinnaformis Hall (in part) [not (Owen)], 1863, Sixteenth Ann. Rept. New York State Cab. Nat. Hist., pp. 

 129-130, PI. VI, figs. 12 and 13 (not figs. 14-16, referred to Lingulella (Lingulepis) acuminata). (The specimens 

 represented by figs. 12, 13, and 15 are referred with doubt to "Lingulepis pinnaformis" and the name matinalis 

 is proposed for them on p. 130 in the event of their proving distinct. The specimen represented by fig. 15 is a 

 dorsal valve of the true ' ' Lingulepis pinnaformis "^Lingulella (Lingulepis) acuminata. See following reference.) 



Lingulepis matinalis Hall, 1863, idem, p. 130, PI. VI, figs. 12 and 13 (not fig. 15, referred to Lingulella (Lingulepis) 

 acuminata). (The specific name matinalis is proposed for the forms represented by figs. 12, 13, and 15 should 

 they prove distinct from those represented by figs. 14 and 16. See preceding reference.) 



Lingulepis pinnaformis Hall (in part) [not (Owen)], 1867, Trans. Albany Inst., vol. 5, p. 107, PI. I, figs. 12 and 13 (not 

 figs. 14-16). (Copy of Hall, 1863, pp. 129-130, PI. VI, figs. 12 and 13; see note following citation above.) 



Lingulepis matinalis Hall, 1867, idem, p. 107, PL I, figs. 12 and 13 (not fig. 15). (Copy of Hall, 1863, PL VI, figs. 12 

 and 13; see note following citation above.) 



Lingulella f matinalis (Hall), Walcott, 1897, Am. Jour. Sci., 4th ser., vol. 3, p. 404. (Merely changes generic reference.) 



Obolus (Lingulella) matinalis (Hall), Walcott, 1899, Mon. U. S. Geol. Survey, vol. 32, pt. 2, p. 443. (Merely changes 

 generic reference.) 



General form rounded ovate, with the ventral valve broadly subacuminate and the dorsdl 

 valve obtusely rounded; valves rather strongly convex, convexity increasing gradually from 

 the margins to the central portion of the shell. Surface of the shell marked by concentric 

 lines and striae of growth and faint interrupted radiating strise; the finer concentric striae fill 

 in the interspaces between the lines of growth. Wlien the outer layer of the shell is exfoliated, 

 the surface is marked by numerous fine, radiating stri^ (PI. VIII, fig. la), and with more or less 

 obsciu-e concentric lines of growth; the radiating striae are particularly strong over the anterior 

 portion of the inner oblique layers or lamellae of the shell. As far as can be determined from the 

 casts of the inner surface it was marked by concentric lines of growth and strong, radiating, 

 flattened striae (PL VIII, fig. le). The shell is formed of a thin outer layer and numerous 

 inner layers or lamellae over the anterior and outer portions ; these inner lamellae over the anterior 

 portions of the shell are oblique to the outer layer, and when the shell is partly exfoliated they 

 appear as imbricating laj^ers, as shown by Plate VIII, figure Ic; the layers of lamellae over the 

 umbo and central portions are strong and give a considerable thickness to the shell. The 

 species vary somewhat in size and in the outline of the valves, as may be seen by comparing 

 the various figures. A ventral valve 11 mm. in length has a width of 11.5 mm. ; another ventral 



