ACROTKETID.E. 689 



ACROTRETA IDAHOENSIS ALTA Walcott. 



Plate LXV, figures 4, 4a-b. 



Aarotreta gemma Walcott (in part) [not Billings], X884, Mon. TJ. S. Geol. Survey, vol. 8, pp. 17-18, PI. I, figs, la 

 and lb (not figs. Ic-f; see below), and (?) PI. IX, figs. 9 and 9a (see also below). (Specimens now referred 

 to Acrotreta attenuata, A. pyxidicula, and A. curvata were included with the specimens representing 4. idahoensis 

 alta when this description of A. gemma was written, A. curvata being figured, PI. I, figs. Id and le. The 

 specimen represented by PI. I, fig. la, is redrawn in this monograph, PL LXV, fig. 4a. Fig. Ic represented 

 a specimen of Acrotreta sabrinse; the specimens represented by figs. If and 9 and 9a are missing.) 



/■ Acrotreta gemma Walcott (in part) [not Billings], 1891, Tenth Ann. Eept. U. S. Geol. Survey, p. 608, PI. LXVII, 

 figs. 5 and 5a (not figs. 5b-e; see below). (Figs. 5 and 5a are copied from figs, la and lb of preceding reference. 

 Specimens now referred to Acrotreta attenuata, A. pyxidicula, A. curvata, and A. primxva were included with 

 the specimens representing A. idahoensis alta in this reference to A. gemma, but only the last two were figured: 

 A. curvata, PI. LXVII, fig. 5b, and^. primseva, PI. LXVII, figs. 5c, 5d, and 5e.) 



^/' Acrotreta gemma Walcott, Hall and Clarke (in part) [not Billings], 1892, Nat. Hist. New York, Paleontology, vol. 

 8, pt. 1, p. 102, figs. 56 and 57 (not fig. 55). (Mentioned in the text, and figures copied from Walcott, 18S4b, 

 PI. I, figs, la and lb. The specimen represented by fig. 55 is referred in this monograph to Acrotreta curvata.) 

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

 figs. 2a and 2c (not figs. 2, 2b, 2d, and 2e; see below). (Figs. 2a and 2c are copied fromWalcott, 1884b, PI. I, 

 figs, la and lb, respectively. Specimens now referred to Acrotreta attenuata, A. pyxidicula, A. curvata, and A. 

 primxva were included with the specimens representing A. idahoensis alta when this description of A. gemma 

 was written, but only the last two were figured: A. curvata, PL LXII, figs. 2e, and A. primxva, PL LXII, figs. 

 2, 2b, and 2d.) ' '■ 



Acrotreta idahoensis alta Walcott, 1902, Proc. U. S. Nat. Mus., vol. 25, p. 588. (Characterized essentially as below 

 as a new variety.) 



This is one of the forms that I included with Acrotreta gemma Billings in the report on 

 the Paleontology of the Eureka district, Nevada [1884b, p. 17J.- It has the broad false area 

 of A. idahoensis Walcott, but the ventral valve is more elevated and the apex does not over- 

 hang the false area. From A. attenuata ]\ieek it differs in having a broad false area. 



A form indistinguishable from Acrotreta idahoensis alta occurs in the Dunderberg shale of 

 the Eureka district section of Nevada. The horizon is higher than that of the type specimen, 

 but there appears to be no way of distinguisliing between the type and the Dunderberg shale 

 specimens. 



A similar but smaller form extends up through from the Dunderberg shale into the 

 arenaceous and calcareous shales at the base of the Pogonip Hmestone, where fossils of the 

 Ordovician fauna occur. 



This form owes its varietal name to its high ventral valve. 



Formation and locality. — Lower Ordovician: (63) At base of Pogonip limestone, northeast of Adams Hill, 

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



Passage beds between the Upper Cambrian and the Ordovician: (201) Arenaceous Pogonip limestone on east 

 slope of ridge east of Hamburg Ridge; and (206a) sandy limestone on Hoosac Mountain; both in the Eureka district 

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



trpper Cambrian: (61) Limestone in the Dunderberg shale [Walcott, 1908f, p. 184], a little south of the Hamburg 

 mine; and (65) limestone on the east side of Sierra Canyon, opposite Pinnacle Peak; both in the Eureka district [Hague, 

 1892, Atlas], Eureka County, Nevada. 



(S4f) 150 feet (45.7 m.) above the Middle Cambrian and 1,075 feet (327.7 m.) below the top of the Upper Cambrian 

 in light-gray sandstone forming No. 4 of the St. Charles formation fWalcott, 1908f, p. 193], in Blacksmith Fork Canyon 

 about 10 miles (16.1 km.) east of Hyrum, Cache County; (34q) shales about 3,800 feet (1,158.2 m.) above the Brigham 

 quartzite [Walcott, 1908a, p. 8], in Wasatch Canyon, east of Lakeview ranch, about 5 miles (8 km.) north of Brigham, 

 Boxelder County; and (15d) thin-bedded blue limestone near Cave Spring on the east side of the Fish Spring Range, 

 about 4 miles (6.4 km.) south of the J. J. Thomas ranch, Juab County; all in Utah. 



Middle? Cambrian: (33n) Limestone pebbles, west front of the Pavant Mountains, at the mouth of Crow Creek, 

 about 4 miles (6.4 km.) east of Fillmore, Millard County, Utah. ^ 



Middle Cambrian : (58) Shaly limestone in upper beds of Secret Canyon shale^east side of New York and Secret can- 

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



(7i) Limestone just west of the summit on the road east of Schellbourne; and (313b) limestones 3 miles (4.8 km.) 

 north-northeast of Schellbourne; laoth in the Schell Creek Range, White Pine County, Nevada. 



(302w) Limestone at Madison Mountain, Montana. ,._ 



62667°— vol 51, pt 1—12 44 i 



