ACROTEETID^. . 659 



(15b) About 1,700 feet (518.2 m.) above the Lower Cambrian and 2,700 feet (823 m.) below the Upper Cambrian, 

 in the shaly limestones and calcareous shales of the Wheeler formation [Walcott, 1908f, p. 181], near Swasey Spring; 

 (3s and 8g) same horizon as 15b, in the eastern part of Wheeler Amphitheater, east of Antelope Springs; (llu) lower 

 portion of the shales forming the Wheeler formation in Rainbow Valley; (4) drift pieces believed to have come from the 

 horizon of 15b, collected near Antelope Springs; (3x) about 2,200 feet (670.6 m.) above the I;Ower Cambrian and 2,200 

 feet (670.6 m.) below the Upper Cambrian in the limestones forming Id of the Marjum limestone [Walcott, 1908f, p. 

 180], 2.5 miles (4 km.) east of Antelope Springs, in ridge east of Wheeler Amphitheater; (llq, Hy, and 30g) about 

 2,350 feet (716.3 m.) above the Lower Cambrian and 2,050 feet (624.8 m.) below the Upper Cambrian, in the limestone 

 forming Ic of the Marjum limestone [Walcott, 1908f, p. 180], 2.5 miles (4 km.) east of Antelope Springs, in ridge east 

 of Wheeler Amphitheater; and (lOy) about 2,900 feet (884 m.) above the Lower Cambrian and 1,500 feet (457.2 m.) 

 below the Upper Cambrian in the central part of la of the Marjum limestone [Walcott, 1908f, p. 179], about 1 mile 

 (1.6 km.) south-southwest of Marjum Pass; all in the House Range [Walcott, 1908f, Pis. XIII and XV], Millard County, 

 Utah. 



(5b and 54s) Dark blue-gray Langston limestone [Walcott, 1908f, p. 198], just above the Cambrian quartzitic 

 sandstones, north side of Twomile Canyon, near its mouth, 2 miles (3.2 km.) southeast of Malade, Oneida County, 

 Idaho. 



(55c and 163) Spence shale member of the Ute limestone [Walcott, 1908a, p. 8], about 50 feet (15.2 m.) above 

 the Brigham quartzite and 2,755 feet (839.7 m.) below the Upper Cambrian, in a ravine running-up into Danish Flat 

 from Mill Canyon; and (59g) limestones immediately overlying the Spence shale member of the Ute limestone [Wal- 

 cott, 1908a, p. 8], in a saddle north of the creek which flows into Mill Canyon from the west; both about 5 miles (8 

 km.) west-southwest of Liberty and 15 miles (24.2 km.) west of Montpelier, Bear Lake County, Idaho. 



(58j) About 1,900 feet (579 m.) above the Lower Cambrian, and 3,100 feet (945 m.) below the Upper Cambrian 

 near the base of the limestone forming 2 of the Stephen formation [Walcott, 1908c, p. 238 (7)], on the east side of Mount 

 Stephen, about 3,000 feet (914 m.) above the Canadian Pacific Railway track east of Field; and (14s) about 2,300 feet 

 (701 m.) above the Lower Cambrian and 2,700 feet (823 m.) below the Upper Cambrian, in the Ogygopsis zone of 

 the Stephen formation [Walcott, 190Sf, p. 210], on the northwest slope of Mount Stephen, above Field on the Cana- 

 dian Pacific Railway; both in British Columbia, Canada. 



A.CROTHELE SUBSIDUA HERA Walcott. 

 Plate LX, figure 9. 



Acrothele subddua hera Walcott, 1908, Smithsonian Misc. Coll., vol. 53, No. 3, p. 87, PL VIII, fig. 15. (Described 

 and discussed as below as a new species. Fig. 15 is copied in this monograph, PI. LX, fig. 9.) 



This variety is separated from Acrothele subsidua (Wliite) by the more elongate outhne 

 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 spurri and the more anterior 

 position of the apex of A. subsidua. An obscurely defined false area begins at the apical open- 

 ing 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 interior surface 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 the shale carrying fragments of Olenellus. It is 

 quite distinct from A. spurri, with wliich 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: (31a) Limestone and interbedded siliceous shales of the Pioche 

 formation [Walcott, 1908a, p. 11], just above the quartzite on east side of anticline, near Pioche, Lincoln County, 

 Nevada. 



L, Acrothele subsidua l^vis n. var. 



This variety is distinguished by the partial or complete absence of the fine granulation 

 on the epidermal layer characteristic of Acrothele subsidua (White). The shells of the variety 

 have the same general outline and form as the species, and vary in size from 3 to 7 mm. in 

 diameter. 



