BRACHIOPODA. 449 



Variety eonradi.] 



Variety CONRADI N. H.Winchell. 



PLATE XXXIII. PIGS. 37-39. 



1880. Orthis eonradi N. H. WINCIIELL. Eighth Annual Report of the Geological and Natural 



History Survey of Minnesota, p. 68. 



Original description: "Shell having the shape and size of Orthis disparilis (Con.), 

 but with a moderately convex entering valve, with from fifty to sixty fine radiating 

 striae on each valve, about half of which disappear before reaching the beak; foramen 

 of the larger valve narrow, of the smaller valve triangular; surface with indistinct 

 growth-bands, but without evident interradial crenulations; on the center of the 

 smaller valve is a flattening that widens from the beak and disappears before reach- 

 ing the margin." 



In the upper portion of the Trenton limestone at Minneapolis, Minnesota, and 

 Decorah, Iowa, also in the "Lower Blue beds" of Wisconsin at Janesville and Beloit, 

 a small form of Orthis, belonging to the 0. perveta group, is constantly met, and to this 

 the name 0. eonradi has been applied by one of the writers. A similar species has 

 been described by Mr. Billings as 0. electra* and was procured in the upper part of 

 limestone No. 2 of the Quebec group at Point Levis, Canada. Although these speci- 

 mens are from a much lower horizon than the present material, yet the size and 

 general external expression are strikingly similar. Of this species Billings writes: 

 "The only differences that can be made out from a comparison with specimens [of 

 0. perveta] from Tennessee and the figures given by Hall in the Palaeontology of New 

 York are, that in 0. perveta the dorsal valve is more convex than it is in 0. electra, 

 and the beak of the ventral valve not so depressed, while at the same time it is more 

 extended. At present I have no means of comparing the interior of the two species. 

 When such a comparison can be made, should no greater differences be disclosed 

 than are afforded by the external characters, I would be disposed to unite the 

 two under one name." (Pal. Foss., vol. i, p. 80.) Some northwestern specimens 

 have the beak as much depressed as in 0. electra. However, it is usually, if not 

 always, more extended than in the latter species, while the dorsal valve seems to be 

 more convex. Dr. White** has doubtfully identified 0. electra as occurring at Fish 

 Spring, House range, Utah. The greater length of the hinge-line, 16 mm. in these 

 specimens, compared with the figures of Canadian examples, the largest of which 

 are only half that length, precludes the possibility of their being alike. The char- 

 acters by which the northwestern shells can be separated from 0. electra are internal. 

 The latter is described as having the dental plates scarcely developed, while no 



*Pal. Foss., vol. 1, p. 70, fig. 72, and p. 217, 1862. 



** Report of U. S. Geog. Surv. west 100th Meridian, vol. Iv, p. 55, 1875. 



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