396 rUOCEEDlNQS OF THE NATIONAL MUSEUM. vol.xxi. 



DESCRIPTION OF NEW SPECIES.' 

 OBOLUS .(LINGULELLA) ARGUTUS, new species. 



Lingula ? mantirula Wiiitk (pars), Expl. and Siir. West of the lOOtli Mcrid., 1874 

 Prolim. Rop., p. 9; (pars) Expl. and Snr. West of the lOOtli Merid., 1875, IV, 

 p. 52, pi. Ill, fig. 2a (uot lig. 26). 



General form ovate, with the ventral valve obtusely acuminate; valves 

 moderately convex. Exterior surface of the shell unknown. Very 

 fine radiating striic and concentric lines of growth occur on tlie outer 

 surface of the inner layer of the shell. The shell appears to be of 

 medium thickness and formed of a thin outer layer and one or more 

 thin inner- layers or lamelhe. The type specimen of the ventral valve 

 has a length of G mm. and a width of 4.5 mm. 



Observations. — This species is founded upon one of the specimens 

 illustrated by White as Lingula f manticula. The broadly ovate form 

 of the ventral valve clearly distinguishes it from that species. From 

 the associated fragments of trilobites, it evidently occurs at a lower 

 horizon, which may be either Upper or Middle C^ambriau. A dorsal 

 valve from the same locality and in a slightly different character of 

 limestone is provisionally referred to the same species. 



In outline this shell resembles 0. {L.) hellm and 0. {L.) belluliis from 

 Newfoundland. It may also be compared Avith 0. {L.) punctatus, from 

 which it differs in being more ovate. 



Formation and Jocality. — lT])per (?) Cambrian, Schellbourne, Schell 

 Creek liange, Nevada. 



Type.—l^o. 27305, II.S.N.M. 



OBOLUS (LINGULELLA) AUGA, new species. 



General form snbcuneate, with the ventral valve obtusely acuminate 

 and the dorsal valve rouiuled acuminate; valves moderately convex. 

 Surface of the shell, as indicated by casts in the fine sandstone, marked 

 by lines of growth and fine, slightly undulating strite. The inner sur- 

 face is marked by somewhat irregularly scattered pits or i)uncta', some 

 of which are unusually large for the size of the shell. The few traces 

 remaining of the shell indicate that it was relatively thin. The largest 

 well-preserved cast of the ventral valve has a length of 5 mm., with a 

 width of 4,5 mm. The dorsal valves are a little shorter, the length 

 and breadth being nearly the same. Casts of the interior of the ven- 

 tral valve show the presence of a rather long area, divided midway by 

 a narrow, clearly defined cast of a pedicle groove; traces of flexure 

 lines are also preserved. The area of the dorsal valve is proportion- 

 ately shorter than that of the ventral valve; traces of the visceral 

 cavity {v) and the base of the main vascular sinuses are also preserved 



'The iignrcs illustrating the mw s])ecies are now made np as plates for a mono- 

 graph of the United States Geological Survey. 



I 



