NO. 1395. CAMBRTAN BRACHTOPODA—WALCOTT. 261 



Doctor Bro^ger's illustration of this species suiigests (). (hnniu.s 

 more than the typical form of <K chriMUiuin'^ as 1 understand und 

 interpret it. "C/yVA/.s 7>^^/vvr' Dsdman, has sometimes been referred 

 to O. cliristlaniice. 



Dr. Curt Gagel described the form usual 1}^ found in the limestone, 

 stating that the surface is covered with strong dichotomous ribs. He 

 found it in drift blocks of the Ceratop\'ge limestone near Belschwitz, 

 also in glauconitic limestone near Preussinch, Holland, and Weblau.'* 



Dr. Ferdinand Roemer calls attention in his description of the drift 

 in the North German plain to the fact that Remele was the first to 

 identify with certainty blocks of the Ceratopyge limestone of Sweden 

 in the drift, the presence of a form like OHhis christianlm being part 

 of the evidence.^ This shell was probably Pledortlik dwrnms. Doctor 

 Roemer states in his description of the Ceratopyge limestone that a 

 small Orthis {lOrthis christianize) predominates. 



Foviiiatlon and locality. — Upper Cambrian. Ceratopyge shale, 

 Russelokken, Christiania, Norway. Borgholm, Oland, Sweden. 



PLECTORTHIS DAUNUS, new species. 



This species differs from (J. r/wistianlse by having simple ribs that 

 increase in number toward the front and lateral margins of the shell 

 by interpolation of new ribs; no true bifurcation of the ribs was 

 observed, A strong median sinus occurs on specimens of the dorsal 

 valve in both shale and limestone. The shell is fibrous and impunctate. 

 No traces have been seen of the fine, rounded, radiating striaj that 

 occur on the broader ribs and interspaces of P. cJuidlanise. This 

 species differs from P. wvinanl by its more transverse form and less 

 simple ribbing of the shell. 



Formation and locality. — Upper Cambrian. Ceratopyge limestone, 

 Toren, Christiania; Slemenestad west of Christiania, Norwa^^ Oland, 

 Borgholm, Sweden. 



PLECTORTHIS DESMOPLEURA Meek. 



Orthis coloradoensis Meek (not Shumard), Proc. Amer. Phil. Soc, fl, 1870, 



p. 425. 

 Orthis desmopleura Meek, U. S. Geol. Sur. Wyoming, Hayden, 1872, p. 295. 



This shell has the general form and external characters of O. wichi- 

 taensis. It differs in being less convex and in the details of the radi- 

 ating ribs. 0. desmopleura differs from O. remnicha in its uniformly 

 smaller size, less convexity, and in the details 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. 



"Bracfi. Camb. nnd Sil. Geschiebe in Diluvium Prov. Ostund Westpreussen, p. 34. 

 t>Lethea Erratica in Pal. Abbordl., II, Pt. 5, 1885, p. 36. 



