NO. 1152. CAMBRIAN BRACIIIOPODA — WALCOTT. -K)! 



vician in tlie liocky Mountain region. It will require thorough, sys- 

 tematic collecting to establish its range detiuitely. 



Formation and locality. — Upper Cambrian and Lower Ordovician, 

 (Jallatin limestone, Crowfoot section, Clallatin range, Yellowstone Na- 

 tional Park, Wyoming; Hamburg shale near the Hahiburg mine. A 

 variety also occurs in the Secret Canyon shale 1,200 feet below the Ham- 

 burg shale. Eureka district, Nevada. 



lieddish, sandy beds west side of Trout Creek, below J>ergen Park, 

 and Cement Creekj 3 miles north of Hot Springs, 8 to 10 miles southeast 

 of Crested Butte, Colorado. 



Shaly limestoncis at base of Knox dolomite, west of top of ( 'opper 

 Itidge, near railroad cut, 11 niiles northwest of Knoxville, Tennessee; 

 also abundantly in the Kogersville shale^ both NNE. and SSVV. of 

 liogersviUe, Tennessee; in thin layers of limestones at base of Knox 

 dolomite along Cowan Creek, Coosa Valley, Cherokee County; also in 

 shaly limestone in suburb of Attala, Alabama; also at same horizon 

 a large variety occurs both on Cowan Creek and in the Oothcaloga 

 Valley, Bartow County, (Jeorgia. 



Types.— ^os. 27311-3, IJ.S.N.M. 



OBOLUS (LINGULELLA) DUBIUS, new species. 



This is a small shell associated witli 0. [L.) ella. It occui-s in the 

 form of casts in argillaceous shale, no traces of the shell substance 

 remaining. The ventral valve averages about 3 mm. in length, and the 

 dorsal valves are a little shorter. A cast of the interior of ihe ventral 

 valve shows the visceral cavity (*') and an unusually strong main vas- 

 cular sinus on each side. Only one specimen shows these characters. 

 Others only faintly indic-ate them. 



The dorsal valve is rounded ovate, and the cast of its interior shows 

 a very short area that extends well out on the cardinal slopes. The 

 interior markings are a portion of the main vascular sinus(;s, which 

 resemble aomewhat in their form and extension those of tiie dorsal valve 

 of 0. {L.) chuarensis. The only muscle scars preserv^ed are the anterior 

 laterals ot the dorsal \alve. 



As far as can be determined by casts, the outer surface is marked by 

 lines of growth and fine, slightly undulating, concentric stria*. 



Observations. — At first I thought the si)e(;imens now referred to this 

 species were the young of O. [L.) ella, and so illustrated them.' There 

 is still considerable doubt as to their si)ecific relation, but in view of their 

 very distinct interior markings I have referred them to a new species. 



Formation and locality. — Middle Cambrian, Chisholm Mine, south- 

 west slope of Ely Mountains, 3 miles northwest of Pioche, Nevada. 



Tj/2>6'.— No. 27314, IJ.S.N.M. 



'Tenth Annual Kept. U. S. Geol. Snr., 1891, pi. Lxvn, figs. 2c, 2d. 



Proc. N. M. vol. xxi 20 



