684 CAMBRIAN BRACHIOPODA. 



A. defressa (figs. 8 and 8') is the same as the elevated ventral valve represented by figure 8c, or 

 that the latter is A. idahoensis alta; neither form should be referred to A. gemma. A. definita 

 (PL LXIV, figs. 2, 2a-g) occurs at the same relative stratigraphic horizon as this species and 

 it is about the same size. It differs in having a lower, less elevated, and less pointed apex 

 on the ventral valve. 



This form owes its specific name to the fact that its ventral valve is depressed. 



Formation and locality. — Middle Cambrian: (14s) About 2,300 feet {701 m.) above the Lower Cambrian and 

 2,100 feel {823 m.) below the Upper Cambrian in the Ogygopsis zone of the Stephen formation [Walcott, 1908f, p. 210], at 

 the great "fossil bed," on the northwest slope of Mount Stephen; (57f) about 2,200 feet (670.6 m.) above the Lower Cam- 

 brian and 2,800 feet (853.4 m.) below the Upper Cambrian in the limestone forming 1 of the Stephen formation 

 [Walcott, 1908f, p. 209], about 0.5 mile (0.8 km.) east of the great ''fossil bed " on Mount Stephen; (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 lime-, 

 stone 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; and (58r) about 1,800 feet (548.6 m.) above the Lower Cambrian 

 and 3,200 feet (975.4 m.) below the Upper Cambrian, in the limestones forming 2 of the Stephen formation [Walcott, 

 1908f, p. 211], in the amphitheater between Mounts Stephen and Dennis; all near Field on the Canadian Pacific 

 Bailway, British Columbia, Canada. 



ACROTEETA EGGEGRUNDENSIS Wiman. 

 Plate LXX, figures 2a-d. 



Acrotreta eggegrundensis Wiman, 1902, Bull. Geol. Inst. Univ. LTpsala, vol. 6, pt. 1, No. 11, p. 55, PI. II, figs. 23-29. 



(Described in German as a new species. The two specimens represented by figs. 29, 27, and 26, and fig. 24 are 



redrawn in this monograph, PI. LXX, figs. 2a-c and 2d, respectively.) 

 Acrotreta eggegrundensis Wiman, Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, pp. 299-300. (Characterized as 



below.) 



This species is of a characteristic Middle Cambrian type of Acrotreta represented in America 

 by A. idahoensis Walcott and A. Jcutorgai Walcott. The surface is marked by unusually strong 

 lines and ridges of growth and the false area is well defined. It is quite distinct from other 

 species of the genus in European formations. 



Carl Wiman [1902, p. 51] refers this species to the Olenellus sandstone series. The bowlder 

 containing it also carried Aparchites ? anderssoni, Hipponicharion mattJiewi, Oholus ( Westonia) 

 tottnicus, Kutorginaf , Torellella Isevigata, and fragments referred to Olenellus. This fauna is 

 essentially Middle Cambrian in its facies, and unless the fragments referred to Olenellus are 

 indisputably of that genus, I am inclined to refer the bowlder and its contained fossils to the 

 Middle Cambrian. The fact that Oholus ( V^estonia) bottnicus is nearly identical with 0. ( W.) 

 finlandensis of the Middle Cambrian of Finland also points to the Middle Cambrian age of 

 the fauna. 



The specific name is derived from Eggegrund Island, the type locality. 



Formation and locality. — Middle? Cambrian: (311) Drift bowlder of coarse-grained, somewhat friable, glauconitic 

 sandstone. No. 3 [Wiman, 1902, p. 57], on Eggegrund Island, about 25 miles {40 hm.) northeast of Gefle, Province of 

 Gefleborg; and (311a) drift bowlder of glauconitic sandstone [Wiman, 1902, p. 57], at Norrskedika, a little northwest 

 of Osthammar, Province of Stockholm; both in Sweden. 



(Slid) Drift bowlder of glauconitic sandstone [Wiman, 1902, p. 57], south of Lumparstrommen, Aland Island, 

 Finland, Prussia. 



Acrotreta emmonsi Walcott. 



Plate LXV, figure 6. 



Acrotreta emmonsi Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 300. (Characterized as below as a new species.) 



Only the interiors of the two valves of this species are known. The one illustrated shows 

 the distinct character of the vascular markings and muscle scars. The only shell with which 

 It can be compared is the dorsal valve of Acrotreta idahoensis Walcott (PL LXV, figs. If, Ig). 

 This shell resembles Oholella, but its corneous test, cardinal muscle scars, and absence of area 

 of the Oholella type prevent a reference to that genus. Fragments of Olenellus occur in the 

 layer of limestone from which the specimens were obtained. 



