424 THE PALEONTOLOGY OF MINNESOTA. 



[Orthis (Dinorthis) pectinella. 



Orthis platys Billings,* from the Chazy limestone at Montreal, Canada, appears 

 to be a closely related species, but can be separated from 0. (D.) deftecta by its convex 

 and deeper ventral valve and more delicate striae. 



Billings identified Strophomena recta Conrad in the Trenton limestone at Ottawa, 

 Canada. His illustrations clearly show that he had specimens of a true Strophomena 

 before him, but not the S. recta Conrad, which is here regarded as the young of 0. 

 (D.) deflecta. For further remarks see Strophomena billingsi, n. sp. 



Strophomena recta Conrad can be seen readily to be an immature condition of 

 0. (ZX) deflecta, by observing the growth lines on mature individuals of the latter 

 species. The original material of both forms was obtained at Mineral Point, Wis- 

 consin, and specimens of both have been collected by the writers at that locality and 

 elsewhere in that state, all from the same geological horizon, and it is evident that 

 the former is the young of the latter. 



Formation and locality. This common species is widely distributed in the Northwest, and is every- 

 where observed to hold an identical horizon. In Minnesota it is restricted to the Trenton limestone in 

 beds known as the "upper building stone," occurring as casts at Minneapolis and St. Paul, and as free 

 shells at Cannon Falls and in Allen Hunt's quarries near fountain. In Iowa near McGregor. In Wiscon- 

 sin it is a characteristic fossil of the "Lower Blue beds" at Mineral Point, Beloit, Janesville, and 

 Dixon, Illinois. In the "Glade limestone" of Central Tennessee a variety of this species is often met 

 with at Lebanon, Murfreesboro and Lavergne. In Kentucky a specimen has been found near the top of 

 the Birdseye limestone at High Bridge. 



Collectors. H. V. Winchell, C. L. Herrick, E. O. Ulrich and the writers. 

 Mus. Reg. Nos. 672, 682, 5060, 5092, 5095, 7790-7794, 7928. 



ORTHIS (DINORTHIS) PECTINELLA (Emmons) Hall. 



PLATE XXXII, FIGS. 31-34. 



1842. Orthis pectinella EMMONS. Geology of New York; Report, Second District, p. 394, fig. 2 (not 



defined). 



1847. Orthis peetinella HALL. Paleontology of New York, vol. i, p. 123, pi. xxxn, fig. 10. 

 1847. Orthis pectinella, var. semiovalis HALL. Ibidem, p. 124, pi. xxxu, flg. 11. 

 1856. Orthis pectinella BILLINGS. Canadian Naturalist and Geologist, vol. i, p. 205, flg. 5. 

 1858. Orthis pectinella ROGERS. Geology of Pennsylvania, vol. ii, p. 818, flg 602. 

 1863. Orthis pectinella BILLINGS. Geology of Canada, p. 165, flg. 147. 

 1880. Orthis charlottte N. H. WINCHELL. Eighth Report, Geological and Natural History Survey 



of Minnesota, p. 67. 



1883. Orthis pectinella HALL. Second Annual Report, N. Y. State Geologist, pi. xxxiv, figs. 39, 40. 

 1889. Orthis pectinella, var. semiovalis MILLER. North American Geology and Palaeontology, p. 359. 

 1892. Dinorthis pectinella HALL. Palaeontology of New York, vol. viii, pt. i, pp. 195, 222, 228, pi. v, 



flgs. 27-33. 



Original description: " Suborbicular or obtusely semioval, wider than long in 

 the proportion of about nine to twelve; cardinal line extended, equal to, or less 

 than, the greatest width of the shell, slightly deflected at the extremities; area 

 moderately large and well defined; shell resupinate, or the area and foramen being 

 principally on the latter valve, or partially common to both; dorsal [ventral] valve 



*Oan. Nat. jind (Jrol., vol. Iv. p. 438. H?. 15. 



