758 CAMBRIAN BRACHIOPODA. 



BiLLINGSELLA MAJOR Walcott. 

 Plate LXXXVI, figures 1, la. 



Billingsella major Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 239. (Characterized as below as a new species.) 

 BiUmgsella major WAhCOTT, 1908, Smithsonian Misc. Coll., vol. 53, No. 3, p. 101, PI. X, figs. 1 and la. (Characterized 

 as in the preceding and as below' as a new species. Figs. 1 and la are copied in this monograph, PI. LXXXVI, 

 figs. 1 and la, respectively.) 



In general form and convexity this shell is related to Billingsella color ado ensis. It differs 

 from it in being larger and in having coarser radiating ribs. It is the Upper Cambrian repre- 

 sentative of the latter species. 



Formation and locality. — ^Tipper Cambrian: (116) "St. Croix sandstone" in excavation on Well's farm, 2 miles 

 (3.2 km.) west of Baraboo, Baraboo quadrangle (U. S. Geol. Survey), Sauk County, Wisconsin. 



Specimens that are somewhat doubtfull}- referred to this species occiir at the following 

 locality : 



Upper Cambrian: (369o) Dolomite above the "Edgewise beds," in a railroad cut, 0.5 mile (0.8 km.) southwest of 

 Elvins, 6 miles (9.G km.) south of Bonneterre, St. Francois County, Missouri. 



( Billingsella marion Walcott. 



Text figures 67A-B. 

 Billingsella marion Walcott, 1908, Smithsonian Misc. Coll., vol. 53, No. 3, p. 102, PL X, fig. 5. (Described and dis- 

 cussed as below as a new species. Fig. 5 is copied in this monograph as fig. 67A.) 



Dorsal valve transverse; beak small, marginal; sides broadly rounded and merging into 

 the broadly round, almost transverse frontal margin; cardinal line a little shorter than the 



greatest width of the valve and sloping very slightly 



^^■'■^'^ ^'s^"^-^.^ ^.^_^_^_,,,_.^j^^ from the beak to outer extremities; on one speci- 



/ \ / ,^ ■ l^M. y^'^'CL the cardinal angle is extended slightly ; greatest 



( 'tfvJil T ( jhHimSBt width about midway of the length; mesial furrow 



-i^Sr \k^a^^K^^ narrow at the beak and gradually widening to a 



■~"^ — — -=-"aw'S^— - ^"t^j^^^^^^—l broad, deep furrow, which divides the valve into 



" two lobes. 



Figure 67.-iSiWmssrfZa marion Walcott. A, Dorsal valve, the «,irf<ife <?month with the excention of a few 



type specimen, showing extension of the cardinal angle and bUrtaCB smOOtn, Wim UlC CXCCpUOn 01 a leW 



a very broad mesial furrow' B, Dorsal valve with obscure (six Or SCVCn) obsCUrC radiating I'ibs Oil each lobe. 



radiating ribs. ,,,„„.,„ A specimen 10 mm. in width has a length of 6 mm. 



The specimens represented are from Locality 581, Middle r _ _ _ <= 



Cambrian on Moimt Stephen, British Columbia (U. S. Nat. OoservattOnS. TlllS spCCICS IS represented by 



Mus. Cat. Nos. 53676a and 53676b, respectively). Figure 67A is ^liree Specimens of the clorsal valvC. They all in- 

 copied from walcott [190Sd, PI. X, fig. 5]. n . , 1 „ ^ ,1 TT7T 77 7 



dicate a thick shell of the BiUingsetla salemens^s 

 (Walcott) type (PL LXXXVII, figs. 3 and 3a). 



The specific name was given for Mrs. L. D. Burhng, who collected the type specimen. 

 Formation and locality.— Middle Cambrian: (581) About 1,830 feet (557.8 m.) above the Lower Cambrian in 

 limestones forming 3b of the Stephen formation [Walcott, 1908c, p. 238 (7)], on the east side of Mount Stephen, about 

 3,000 feet (914.4 m.) above the Canadian Pacific Railway track, 3.5 miles (5.6 km.) east of Field, British Columbia, 

 Canada. 



Billingsella obscura Walcott. 

 Plate LXXXVI, figure 6. 

 Billingsella obscura Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 239. (Characterized as below as a new species.) 

 This species is founded on a single dorsal valve that occurs in the form of a cast in sand- 

 stone. It is transverse, width 18 mm., length 13 mm.; moderately convex, with a slightly 

 defined mesial flattening that broadens out nearly to three-fiftlis the width of the shell at the 

 front margin. The surface of the cast is marked by a few faintly defined, rather broad costae. 

 The shell is much like the large dorsal valves of Billingsella coloradoensis . It differs in its 

 broader frontal margin and median flattening. 



Formation and locality.— Middle Cambrian: (74) Sandstone about 300 feet (91.4 m.) above the base of the 

 Tonto group at the head of Nunkoweap Valley, Grand Canyon of the Colorado, Arizona. 



