BRACHIOPODA. 395 



^trophomena trilobata. 1 



STROPHOMENA TBILOBATA Owen, sp. 



PLATE XXXI, FIGS. 12 and 13. 



1852. Leptcena trilobata OWEN. Geological Survey of Wisconsin, Iowa and Minnesota, p. 584, 



pi. n, flgs. 17, 18. 

 1877. Strophomena trilobata MILLER. American Palaeozoic Fossils, p. 138. 



Original description: "This species was at first referred to the species deltoidea, 

 but the form is so decidedly different in several respects that it seems to constitute 

 a distinct species. Dorsal valve broadly trilobate, very gibbous in front and depressed 

 towards the hinge-line; margin undulating, semioval; ventral valve concave; hinge- 

 line extended; fine and equally radiating striae, partaking of the curvature of the 

 surface of the shell. 



"The outline of this shell is much more undulating, shell more gibbous and 

 broader, and more distinctly trilobate than the deltoidea. 



" It occurs in the shell-beds F. 3A, near the Agency, on the Turkey river, Iowa." 



Owen's illustrations, and his statement that the shell is "very gibbous in front 

 and depressed towards the hinge-line," leaves very little doubt that S. trilobata is 

 identical with a species occurring in the middle beds of the Galena in Minnesota. 

 It is true that associated with these specimens are also very gibbous examples of 

 Rafinesquina deltoidea. These, however, are never as flat on the central disc nor have 

 they the nasute anterior margin of S. trilobata. To 6 r . fluctuosa this species is closely 

 related, but can be distinguished by the following features: The flat central disc is 

 comparatively smaller, the shell anteriorly is twice as long and incurved, while in 

 S. fluctuosa it is always flat, and the ventral cardinal area is strongly retrose. The 

 interior characters and the corrugation of the flat central disc are, as far as can be 

 determined, essentially as in 5. fluctuosa. 



Formation and locality. The species is abundant in the middle beds of the Galena horizon, but 

 since it usually occurs as natural casts it is not often gathered by collectors. It occurs at Kenyon and 

 elsewhere in Goodhue county, Mantorville, Old Concord and near Rochester, Minnesota. Turkey river 

 Iowa. Probably also in the Galena of Wisconsin. 



Collectors. A. D. Meeds, W. H. Scofleld, M. W. Harrington and N. H. Winchell. 

 Mus. Reg. Nos. 208, 293, 369, 371, 391, 7253. 8189, 8190. 



STROPHOMENA FLUCTUOSA Billings. 



PLATE XXXI, FIGS. 14-17. 



1860. Strophoi.iena fluctuosa BILLINGS. Canadian Naturalist and Geologist, vol. v, p. 57, flg. 6 



1862. Strophomena fluctuosa BILLINGS. Palaeozoic Fossils, vol. i, p. 123, flg. 102. 



1863. Strophomena fluctuosa BILLINGS. Geology of Canada, p. 209, fig. 207. 



1892. Strophomena fluctuosa HALL. Palaeontology of N. Y., vol. viii, pt. i, p. 251, pi. xiA, flgs. 4, 5. 



