424 
THE PALEONTOLOGY OF MINNESOTA. 
LOrthis (Dlnorthis) 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.) defleda 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 hillingsi, n. sp. 
Strophomena recta Conrad can be seen readily to be an immature condition of 
0. (D.) 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 XX.XII. FIGS. M-U. 
1842. Orthis pectinella Emmons. Geology of New York; Report, Second District, p. 394, fig. 2 (not 
defined). 
1847. Orthis pectinella Hall. Palaiontology of New York, vol. i, p. 123, pi. xxxii, fig. 10. 
1847. Orthis pectinella, var. semiovalis Hall. Ibidem, p. 124, pi. xxxu, fig. 11. 
18.56. Orihis pectinella Billings. Canadian Naturalist and Geologist, vol. i, p. 205, tig. 5. 
1858. Orthis pectinella Rogers. Geology of Pennsylvania, vol. ii, p. 818, tig 602. 
1863. Orthis pectinella Billings. Geology of Canada, p. 165, flg. 147. 
1880. Orthis charlottce 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, flgs. 39, 40. 
1889. Orthis pectinella, var. semiovalis Miller. North American Geology and Paheontology, p. 359. 
1892. Dinorthis pectinella Hall. Paheontology of New York, vol. viii, pt. i, pp. 195, 222, 228, pi. v, 
figs. 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 gi-eatest width of the shell, slightly deflected at the extremities; area 
moderately large and well defined; shell resupinate, or the area and foramen being 
princip ally on the latter valve, or partially common to both; dorsal [ventral] valve 
*Can. Nat. and (Jeol.. vol. iv. p. 438, fig. l.> . 
