310 PllOCEKDlNGS OF THE NATIONAL MUSEUM. vol. xxviii. 



KUTORGINA PERUGATA, new species. 



GenGrul t'(jnn ovate, biconvex. Surface marked by concentric lines 

 of growth and more or less strong* concentric corrugations; the outer 

 surface is ornamented by a tine network of ol)lique, depressed lines, 

 that leave minute rhomboidal elevations ))etween them that look like 

 fine i)apillie under a moderately strong magnifier, and the cast of the 

 surface has much the same appearance in a transverse light. Shell 

 sul)stance calcareous. 



A large ventral valve has a length of li mm. ; width. 16 mm. A 

 dorsal valve 11 mm. in length has a width of 11 mm. 



The ventral valve is strongly convex in adult shells, with the highest 

 point near the umlx) or at the apex. The apex terminates at or over- 

 hangs a rudimentary pseudo area that slopes beneath the shell at an 

 angle of la to 60 to the plane of the margins of the \alve. The 

 pseudo area is concave and about half the length of the space between 

 the apex and the plane of the valve. Casts of the interior show well- 

 delined main vascular sinuses, with the outline of the visceral area 

 between them. 



The dorsal \alve is transverse, nearly Hat in some examples, and 

 slightly convex in others. The surface slopes gradually from the 

 margins to near the umbo, where the slope increases and extends to 

 the upward-pointing apex. A rudimentary pseudo area slopes back- 

 ward from the apex. In some examples the pseudo ai"ea appears to 

 ])e little more than a bending over of the posterior margins of the shell; 

 in others it has the outline of a slightly convex pseudodeltidium. 



Olm-ri'afionH. — This species, in its reticidate surface ornamentation, 

 recalls [plikhAla pwiiinda "and Mlckwltzia ■monilifevd. In form the 

 young shells are not unlike Kutorgiva cingulata. A large, imperfect 

 ventral valve, 21 mm. by 21 mm., of this genus, was collected by Mr. 

 ,]. E. Clayton from the Cambrian limestone of the Silver Peak dis- 

 trict. It ma}" belong to K. 2>eragata^ and it is so referred for the 

 present. From the shales of the Olenellus zone in Silver C^anyon, 

 White Mountain range, a series of compressed specimens were col- 

 lected. Some of these show a concave pseudo area on the ventral 

 valve, also strong main vascular sinuses. Some of the shells from 

 the shales north of Red ^Mountain have lost all traces of surface char- 

 acters, only a faint, smooth impression remaining. 



Formation and locality. — Lower Cambrian. Calcareous shales 

 beneath Archceocyathus limestone, 8 miles north of Valcadi Spring or 

 1 miles northwest of Drinkwater Mine; summit on road 10 miles 

 southwest of town of Silver Peak; also on divide between Clayton 

 and Fish Creek valleys, north of Red Mountain, Silver Peak Range; 

 Silver Peak District, Esmeralda County, Nevada. About 1,000 feet 

 abov(^ quartzite, Silver Can3^on, White Mountain Range, Nevada. 



