BILLINGSELLIDtE. 777 



90 miles (145 km.) south-southwest of Konigsberg; and (386b) drift blocks of "Glauconite limestone" near Wehlau, 

 30 miles (48 km.) east of Konigsberg; all [Gagel, 1890, p. 34] in East Prussia, Germany. 



(323z) Ceratopyge limestone at Toien, near Christiania; and (8x) Ceratopyge limestone at Slemmestad, about 3 miles 

 (4.83 km.) southwest of Christiania; both in Norway. 



(323h) Blue Ceratopyge limestone at Vestfossen; and (323f) lower part of tbe Ceratopyge liinestone at Vestfossen; 

 both [Brogger, 1882, p. 17] 10 miles (16.1 km.) west-southwest of Christiania, Norway. 



(310j) Ceratopyge limestone at Borgholm; and (310 [Moberg and Segerberg, 1906, description of PI. Ill]) Ceratopyge 

 limestone (zone 4) at Ottenby; both on Oeland Island, Sweden. 



EooRTiiis DESMOPLExiRA (Meek). 



Plate XCVI, figures 1, la-r. 



Not Orthis coloradoensis Shumaed, 1860, Trans. Acad. Sci. St. Louis for 1856-1860, vol. 1, p. 627. (Referred in this 



monograph to Bittingsella.) 

 Orthis coloradoensis Meek [not Shumard], 1870, Proc. Am. Philos. See, vol. 11, No. 84, p. 425. (Described as a new 



species.) 

 Orthis desmopleura Meek, 1872, U. S. Geol. and Geog. Terr., Geol. Survey Wyoming, Prelim. Kept., p. 295. (Merely 



proposed as a new specific name, coloradoensis being preoccupied.) 

 Orthis {Plectorthis) desmopleura (Meek), Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 261. (Characterized.) 



This shell has the general form and external characters of E. wichitaensis (Walcott) . It 

 differs in being less convex and in the details of the radiating ribs. The illustrations of the 

 two species will serve as a basis of comparison. Eoorthis desmopleura differs from E. remnicJia 

 (N. H. Winchell) in its uniformly smaller size, less convexity, and in thedetaUs of the radiating 

 ribs. The ribs have a wide range of variation, but when from the same character of matrix they 

 are all of the same type and the shells grade from one to the other. The ventral valves of 

 young shells 2 to 3 mm. long are highly convex and usually appear to be a little longer than wide ; 

 if in such shells the surface striae are in sharply elevated fasciculse, the result is to all appearances 

 a rhynchoneUoid shell. 



The interior of the ventral valve shows a narrow area, broad delthyrium, spondylium 

 almost free from the bottom of the valve, and a median septum that may have supported the 

 front end of the spondyUum. In young and strongly convex shells the spondylium is narrow 

 and very strongly defined. The narrow area of the dorsal valve is divided by a broad delthy- 

 rium, in the center of which is a very slightly developed cardinal process. 



The Wyoming variety of this species occurs in abundance in the Bighorn Mountains. 

 The specimens illustrated on Plate XCVI show the characteristic features of the species as it 

 occurs in Colorado, and also some phases of it not observed there. The typical form is 

 illustrated by figure Ih. For the variety the name of E. desmofleura nympha is used (PI. 

 XCVI, fig. 2). 



Eoorthis Tiamiurgensis (Walcott) [1884b, p. 73] is closely related to E. desmopleura smd may 

 be identical with it. Eoorthis melita (HaU and Whitfield) [see Leptsena melita HaU and Whit- 

 field, 1877, p. 208] from the Pogonip Lower Ordovician limestone is near to the less convex, 

 more evenly striated forms of E. desmopleura. It is probably not more than a variety of the 

 latter. Schuchert's reference of the species L. melita to Dalmanella [1897, p. 202] does not 

 appear to be correct, as it has the pseudodeltidium of Eoorthis. 



Formation and locality. — Lower Ordovician: (360f) Siliceous liinestone at Glen Eyre, Queens Canyon, north- 

 east of Manitou; (360a) red siliceous limestone on west side of Trout Creek below Bergen Park, 7 miles (11.2 km.) 

 north-northwest of Manitou; (186 and 186a) near line of contact between red and gray Ordovician limestone, in 

 siliceous red limestone about 30 feet (9.1 m.) above. the pre-Cambrian rocks, Williams Canyon, Manitou; (187) red 

 siliceous limestone 105 to 122 feet (32 to 36.7 m.) above the pre-Cambrian rocks, 2 miles (3.2 km.) below Manitou Park 

 Hotel; and (360) red siliceous limestone near Colorado Springs; all in El Paso County, Colorado. 



(105t) Limestone [Walcott, 1908f, p. 173] at the summit of Notch Peak, House Range, Millard County, Utah. 



(185z) Limestones at the base of the Lower Ordovician [Walcott, 190Sf, p. 191] in Blacksmith Fork Canyon, about 

 9 miles (14.4 km.) east of Hyrum, Cache County, Utah. 



Passage heds between the Upper Cambrian and the Ordovician: (34g) Limestone about 1,000 feet (305 m.) above 

 the valley on the east side of the Fish Spring Range, just west of the high point southwest of the J. J. Thomas ranch, 

 Tooele County, Utah. 



