OBOLID^. 495 



Obolus (Lingulella) dubius Walcott, 1898, Proc. U. S. Nat. Mus., vol. 21, p. 401. (Described and discussed essen- 

 tially as below as a new species.) 



lAngulella genei Pack, 1906, Jour. Geology, vol. 14, No. 4, p. 295, PL I, figs. 3, 3a-b. (Described and discussed as a 

 new species.) 



This is a small shell associated with Oholus ( Westonia) ella (Hall and Whitfield). It occurs 

 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 Uttle shorter. A 

 cast of the interior of the ventral valve shows the visceral cavity (v), and an unusually strong 

 main vascular sinus (vs) on each side. Only one specimen shows these characters as illustrated 

 by Plate XXIV, figure 4; others only faintly indicate them. 



This dorsal valve is I'ounded 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 sinuses, which, in their form and extension, somewhat resemble those of the dorsal 

 valve of 0. ( W.) chuarensis (Walcott) . The only muscle scars preserved are the anterior laterals 

 of the dorsal valve. 



As far as can be determined from the casts, the outer surface is marked by lines of growth 

 and fine, slightly undulating concentric striae. 



Observations. — At first I thought the specimens now referred to this species were the young 

 Oholus (Westonia) ella, and so illustrated them [1891a, PI. LXVII, figs. 2o and 2d]. There is 

 still considerable doubt as to their specific relations, but in view of the very distinct interior 

 markings I have referred them to a new species. 



The form described by F. J. Pack [1906, p. 29.5] as "Lingulella genei" comes from the same 

 locahty and band of shale as L. duhia, and has the same form and strong interior markings. 

 Some of Pack's specimens show the cast of the exterior surface. This is marked by the very 

 fine, concentric, shghtly undulating hues so typical of Lingulella. The best-preserved casts of 

 the surface do not present the characteristics of the surface of Obolus ( Westonia) ella. 



Formation and locality. — Middle Cambrian: (31) Shales at the Chisholm mine, southwest slope of Ely Mountains; 

 and (333 [Pack, 1906, p. 295]) shales on the dump of the Abe Lincoln mine; both near Pioche, Lincoln County, Nevada. 



Lingulella ellsi (Walcott). 

 Plate XIX, figures 3, 3a-c. 



Oholus {Lingulella) ellsi Walcott, 1898, Proc. U. S. Nat. Mus., vol. 21, p. 402. (Described and discussed as below 

 as a new species.) 



Shell small, broad ovate in outline, with the ventral valve obtusely acuminate, and the 

 dorsal valve broadly rounded; valves appear to have been moderately convex, judging from 

 their appearance in the siUceous shale. The surface of the shell is marked by rather strong, 

 concentric lines and striae of growth, the strise apparently indicating a slightly lamellose surface; 

 very fine radiating striae occur on the surface of the inner layers of the shell. A ventral valve 

 3.5 mm. in length has a width of 2.75 mm.; the dorsal valve is a httle shorter than the ventral 

 valve. 



Partial casts of the interior of the ventral valve show a very clearly defined area that 

 extended as a shelf on each side of the rather deep, narrow, pedicle furrow; portions of the 

 casts that fill the undercut may be observed in several specimens; the flexure hues are narrow, 

 shai-p, and situated well out toward the lateral margins. The cast of the visceral area of the 

 ventral valve extends about one-third the distance from the area to the anterior margin; it is 

 not well defined, and no traces of muscle scars have been detected; of the vascular system 

 only the base of the main sinuses is shown in any of the casts. 



Observations. — This very pretty little species is closely related in form to Lingulella rotunda 

 (Matthew), and comparison should also be made with the more rotund variety of L.ferruginea 

 Salter. It occurs in association with Acrothele pretiosa (Billings). 



