CAMBRIAN DRACHIOPODA — WALCOTT 87 



Doubtfully: Lower Cambrian sandy shales 2.5 miles (4.02 km.) 

 south of Barrel Spring- and .5 mile (.80 km.) east of the road, Silver 

 Peak quadrangle (U. S. G. S.), Esmeralda County, Nevada. 



ACROTHELE SUBSIDUA HERA, new variety 



Plate 8, Figure 15 



This variety is separated from Acrothele subsidua White [1874, 

 p. 6] by the more elongate outline of the ventral valve, and more 

 posterior position of the apex, the relative position of the latter being 

 between the posterior position of the apex of Acrothele spiirri (see 

 p. 86) and the more anterior position of the apex of A. subsidua. 

 An obscurely defined false area begins at the apical opening and 

 ■diverges toward the margin. It is marked by a slight median ridge. 

 The exterior layers of the shell are exfoliated, carrying with them 

 the outer portion of the apical opening. The inner portion is rather 

 large, and from the presence of an elongate tubercle on each side 

 it is apparent that there was a similar tubercle on the exterior sur- 

 face on each side of the apex a little in advance of the opening. 



The surface of an interior layer is marked by fine concentric 

 lines, numerous very fine radiating lines, and four sharp ridges that 

 radiate from the apex to the front margin. 



Observations. — This species is represented by a single specimen 

 that occurs in the buff-weathering, gray limestone interbedded in a 

 shale carrying fragments of Olenellus. It is quite distinct from A. 

 spurri, with which it is associated, and appears to be a progenitor of 

 A. subsidua, which occurs so abundantly in the Middle Cambrian 

 strata much higher up in the section. 



Formation and Locality. — Lower Cambrian : Associated with 

 Olenellus in the shales and thin interbedded layers of limestone of 

 the Pioche formation [Walcott, 1908a, p. 11], just above the quartz- 

 ite on east side of anticline, near Pioche, Lincoln County, Nevada. 



ACROTHELE TURNERI, new species 



Plate 9, Figure 12 



General outline broad oval, ventral valve slightly conical, with the 

 apex at about the posterior third of the length of the valve; apex 

 short and perforated on the back side of its point by a minute pedicle 

 opening ; false area indicated by a slight flattening between the apex 

 and posterior margin. Dorsal valve gently convex ; beak marginal. 



Surface marked by fine concentric lines and striae of growth. 

 ■Shell corneous and made up of a few very thin lamellae. 



