790 CAMBRIAN BRACHIOPODA. 



Observations. — This species was at first compared with Nisusia {Jamesella) nautes (Walcott) 

 (PL XCIII, figs. 6, 6a-b), but the surface ribs are more regular and less numerous. It also 

 occurs 1,800 feet higher in the stratigraphic section than N. (J.) nautes. 



Formation and locality. — Middle Cambrian: (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 limestones forming Id of the Marjum limestone [Walcott, 190Sf, 

 p. 180]; and (llq) about 2,350 feet (716.3 m.) above the Lower Cambrian, and 2,050 feet (624.8 m.) below the Upper 

 Cambrian, in the limestones forming Ic of the Marjum limestone [Walcott, 1908f, p. 180]; both 2.5 miles (4 km.) east 

 of Antelope Springs, in ridge east of Wheeler Amphitheater [Walcott, 1908f, Pis. Xlll and XV], House Range, Millard 

 County, Utah. 



EOOETHIS TULLBEEGI (Walcott). 



Plate XCV, figure 3. 



Orthis {Plectorthis) tullbergi WAhcoTT, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 271. (Characterized as a new species.) 



Orthis {Plectorthis) tullbergi Walcott, Moberg and Segerberg, 1906, Medd. fran Lunds Geol. Faltklubb, Ser. B, 



No. 2 (Aftryck ur K. Fysiografiska Siillskapets Handl., N. F., Bd. 17), p. 69, PI. II, fig. 3. (Characterized 



in Swedish. Fig. 3, in common with the remaining figures on PI. 11 of Moberg and Segerberg's paper, was 



copied from a preliminary photograph of PI. XCV of this monograph.) 



The transverse outline and simple strong ribs of Eoorthis tullbergi serve to distmguish it 

 from E. christianise. (Kjerulf) and E. daunus (Walcott). 



Moberg and Segerberg [1906, pp. 69-70] are inclined to consider this form as identical 

 with Eoortliis christianix. Since reading their remarks and conclusions I have studied the 

 material representing the two forms Eoortliis christianise, and E. tullbergi and have decided 

 to leave the latter as a distinct species. There may be a complete gradation of form and surface 

 characters between the two shells, but I do not find it in the numerous specimens before me. 



The specific name was given in honor of Mr. S. A. Tullberg. 



Formation and locality. — Passage beds between the Upper Cambrian and the Ordovician: (390) Boundary 

 stratum between the Orthoceras limestone and the Ceratopyge limestone [Moberg and Segerberg, 1906, p. 69], at 

 Alunbruk (alum works), southern part of Oeland Island, Sweden. 



EOOETHIS WICHITAENSIS (Walcott). 



Plate XCIV, figures 1, la-o, lu. 



Orthis {Plectorthis) vAchitaensis Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, pp. 271-272. (Characterized essen- 

 tially as below as a new species.) 



In general form and outline this shell is related to Eoortliis desmopleura (Meek) and 

 E. remnicha (Wincbell). Its convexity and differences in the radial ribbing and striation sep- 

 arate it from the former species, and it occurs in an older geological formation. Its convexity 

 and surface characters distinguish it from E. remnicha. The series of figures illustrating the 

 species will enable the student to study all that is known to me of the species. 



A considerable nuxnber of relatively smooth shells that occur in the collection are desig- 

 nated as the variety Iseviusculus, but it is often difficult to separate them from the more finely 

 ribbed specimens that are typical of the species. 



Formation and locality. — lower Ordovician: (360a) Red siliceous limestone on west side of Trout Creek, 

 below Bergen Park, 7 miles (11.2 km.) north-northwest of Manitou, El Paso County, Colorado. 



TTpper Cambrian: (13j) Lower part of Arbuckle limestone at Small Hill, 2 miles (3.2 km.) southwest of Signal 

 Mountain, about 8 miles (12.8 km.) west of Fort Sill; and (9z) basal beds of the Arbuckle limestone, about 25 feet above 

 the heavy-bedded limestone, near the middle of the west half of sec. 13, T. 4 N., R. 13 W., about 13 miles (20.8 km.) 

 northwest of Fort Sill; both in Comanche County, Oklahoma. 



(9q) About 10 feet (3 m.) above the porphyry contact and 90 feet (27.4 m.) below the Arbuckle limestone in 

 limestones of the Reagan sandstone, in middle of west half of sec. 2, T. 4 N., R. 13 W. ; (9u) about 195 feet 

 (59.4 m.) above the porphyry contact in the limestones of the Reagan sandstone, in SE. J NE. -J .sec. 2, T. 4 N., 

 R. 13 W.; (9s) about 85 feet (26 m.) below the Arbuckle limestone in the limestones of the Reagan sandstone, near 

 middleof west half of sec. 13, T. 4N., R. 13 W.; all about 15 miles (24.2 km.) northwest of Fort Sill, Comanche County, 

 Oklahoma. 



(13k) Limestones of the Reagan sandstone (in the section 7 miles (11.2 km.) north of Springer this horizon is 

 about 225 feet (69 m.) above the porphyry contact and 55 feet (17 m.) below the Arbuckle limestone), on the west 



