ACROTRETID^. 675 



in a ravine on the east side of the road about 1 mile (1.6 km.) southwest of Emigrant Pass; and (7v) shales of the Emigrant 

 formation [Turner, 1902, p. 265], 4.25 miles (6.8 km.) south-southeast of Emigrant Peak; all in the Silver Peak quad- 

 rangle (U. S. Geol. Survey), Esmeralda County, Nevada. 



!, ACEOTEETA ATTENUATA Meek. 



Plate LXIV, figures 1, la-o; Plate LXXIX, figures 6, 6a. 



Acrotreta attenuata Meek (in part), 1873, Sixth Ann. Kept. U. S. Geol. and Geog. Survey Terr, for 1872, p. 463, footnote. 

 (Listed as A. subconica Kutorga, and described in footnote as a possible new species. Specimens now referred 

 to A. attenuata var.? and A. idahoensis were also included in this reference.) 



Acrotreta gemma Walcott (in part) [not Billings], 1884, Mon. U. S. Geol. Survey, vol. 8, pp. 17-18. (Specimens 

 representing Acrotreta pyxidicula, A. curvata, and A. idahoensis alta were included with the specimens repre- 

 senting A. attenuata when this description of A. gemma was written, but only the last two are known to have 

 been figured: A. curvata, PL I, figs. Id and le; and A. idahoensis alta, PL I, figs, la and lb. The specimens 

 represented by PL IX, figs. 9 and 9a, can not be found at this time, but it is probable that they should be 

 referred to A. idahoensis alta. Fig. Ic represented a specimen of Acrotreta sabrinx, and the specimen repre- 

 sented by fig. If is missing.) 



Acrotreta gemma Walcott (in part) [not Billings], 1886, Bull. U. S. Geol. Survey No. 30, pp. 98-99. (Specimens 

 now referred to Acrotreta pyxidicula and A. primmva were included with the specimens representing A. attenuata 

 when this description of A. gemma was written, A. primseva being figured, PL VIII, figs. 1, la-b.) 



Acrotreta gemma Walcott (in part) [not Billings], 1891, Tenth Ann. Kept. U. S. Geol. Survey, p. 608. (Specimens 

 now referred to Acrotreta pyxidicula, A. curvata, A. idahoensis alta, and A. primseva were included with the 

 specimens representing A. attenuata in this reference to A. gemma, the last three being figured: A. curvata, 

 PL LXVII, fig. 5b; A. idahoensis alta, PL LXVII, figs. 5 and 5a; and A. primseva, PL LXVII, figs. 5c, 5d, and 5e.) 



Acrotreta gemma Walcott (in part) [not Billings], 1899, Mon. U. S. Geol. Survey, vol. 32, pt. 2, p. 449. (Specimens 

 now referred to Acrotreta pyxidicula, A. curvata, A. idahoensis alta, and A. primseva were included with the 

 specimens representing A. attenuata when this description of A. gemma was written, the last three being figured: 

 A. curvata, PL LXII, fig. 2e; A. idahoensis alta, PL LXII, figs. 2a and 2c; and A. primseva, PL LXII, figs. 2, 

 2b, and 2d.) 



Acrotreta attenuata Meek, Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 298. (Characterized.) 



The variations in the exterior form of the ventral valve of this species are so fully shown 

 by the illustrations that it is unnecessary to enter into* detailed description. The species is 

 characterized by its elevated ventral valve and narrow, incurved false area. The specimens 

 illustrated by Plate LXIV, figures 1, la, lb, and Ih, are from the material labeled by Meek as 

 Acrotreta attenuata, and all the others are from the same geological area. Some of the forms of 

 A. idahoensis alta (PI. LXV, fig. 4) look like A. attenuata, but the false area is different. Acro- 

 treta lnutorgai has a somewhat similar false area and elevation, but it is a less robust shell and 

 the apex of the ventral valve is nearer the posterior margm. The former reference to A. gemma 

 is explained under the description of the genus (p. 673). Shells with a distinctly marked false 

 pedicle groove in the ventral valve occur in the shales of the Wlaeeler formation of the Middle 

 Cambrian of the House Range, Utah. The shells of this locality show fine interiors of both 

 valves (PL LXIV, figs, li-n, and PI. LXXIX, figs. 6, 6a). The interiors of the ventral valve 

 are much like those of A. Jcutorgai Walcott (PI. LXV, figs. 3b, 3c). 



Formation and locality. — Upper Cambrian: (61) Limestone in the Dunderberg shale [Walcott, 1908f, p. 184], 

 a little south of the Hamburg mine. Eureka district [Hague, 1892, Atlas], Eureka County, Nevada. 



Middle Cambrian: (59) Limestone at the base of the western slope of Combs Peak, near the plain of Antelope 

 Valley, Eureka district [Hague, 1892, Atlas], Eureka County, Nevada. 



(3s) 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, 1908t, p. 181] in the eastern part of 

 Wheeler Amphitheater, east of Antelope Springs, House Range [Walcott, 1908f, Pis. XIII and XV]; (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 the limestone forming la of the Marjum limestone [Walcott, 1908f, p. 179], about 1 mile (1.6 km.) south -southwest of 

 Marjum Pass, House Range [T^'alcott, 1908f, PL XIII]; and (3x) about 2,200 feet (670.6 m.) above the Lower Cambrian 

 and 2,200 feet (670.6 m.) below the Upper Cambrian in the shaly limestones forming Id of the Marjum limestone 

 [W^alcott, 19081, p. 180], 2.5 miles (4 km.) east of Antelope Springs, in ridge east of Wheeler Amphitheater, House 

 Range [Walcott, 1908f, Pis. XIII and XV]; all in Millard County, Utah. 



(9h) At the base of the limestone above the Wolsey shale [Walcott, 19081, p. 202] on Beaver Creek, 5 miles (8 km.) 

 north of York, and about 8 miles (12.8 km.) north of Canyon Ferry, Big Belt Mountains, Fort Logan quadrangle (U. S. 

 Geol. Survey), Meagher County; (159) limestones north of West Gallatin (Gallatin) River, Gallatin County; (302) 



