BRACHIOPODA. 461 
riety laticostata.] 
This species is known in America as Rhynchonella increbescens Hall, but unfortun- 
ately it must give way to R. inequivalvis, a name defined and illustrated four years 
earlier by Castelnau. The latter obtained his specimens from the “ Magnesian lime- 
stone, Drummond’s island.”+ Of the Trenton brachiopods, this is the most persistent 
and serves as a good marker of this formation. Associated with Orthis subcequata, it 
at once establishes the outcrop as of Trenton age. 
Formation and locality.—In the upper two-thirds of the Trenton limestone at Minneapolis, Minne- 
sota. Very common in the Trenton shales at Minneapolis, St. Paul, Cannon Falls, Chatfield, Lanesboro, 
Fountain, Eyota, Preston and near Caledonia, Minnesota; Decorah and McGregor, Iowa. Also common 
in the lower portion of. the Galena in Goodhue and Fillmore counties, Minnesota. In the ‘‘ Lower Blue 
beds” at Janesville, Beloit and Mineral Point, Wisconsin. In the Trenton at Dixon, Illinois; Auburn, 
Lincoln county, Missouri; Frankfort, Danville and Lexington, Kentucky; Nashville and elsewhere in 
Tennessee; Middleville, Trenton Falls, Watertown and other places in New York: Ottawa, Canada, and 
Drummond’s island. In the Galena at Oshkosh and Neenah, Wisconsin. ‘Two specimens have also been 
collected by one of the writers in the Hudson River group at Savannah, Illinois. 
Collectors——Miss C. L. Seymour, C. L. Herrick, J.C. Kassube, U.S. Grant, H. V. Winchell, W. H. 
Scofield, E, O. Ulrich and the writers. 
Mus. Reg. Nos. 266, 323, 328, 331, 370, 382, 650, 3493, 3516, 3517, 4053, 4925, 4933, 4941, 4999, 5128, 
5473-5476, 5478, 5479, 5482, 5484, 5488, 5490, 5491, 5493, 5496, 5497, 5506, 5508, 5509, 5513, 5515, 5516, 5518, 
5519, 5522, 5852, 5858, 5583, 6486, 6764, 6777, 6790, 6793, 6799, 6800, 7918, 8209-8218. 
Variety LaticostatTa W. and SV. 
PLATE XXXIV, FIGS. 26—29. 
1892, Aprill. Rhynchotrema inceequivalvis, var. laticostata W. and S. American Geologist, vol. ix, 
1892, April 9. Rhynchonella Se ape Bulletin of the Minnesota Academy of Natural 
Sciences, vol. iii, p. 333, pl. Iv, figs. 19-20. 
In the lower portion of the Galena south of Cannon Falls Rf. inwquivalvis often 
attains a far greater width than is usual for the species. The four plications of the 
fold are closely arranged, while the five or six on the side are spread out and are 
therefore larger than usual. These shells, if found alone, would be regarded at once 
as a distinct species. Their development begins in the lowest portion of the Galena 
shales, where specimens are sometimes picked up at St. Paul. However, it is not 
until this species is found in association with Clitambonites diversa Shaler that the 
variety becomes common and attracts attention. In the Trenton of New York and 
Kentucky an occasional specimen is found which approaches vay. laticostata, but none 
of them is so strongly transverse as Minnesota individuals. 
Collectors.—W. H. Scofield and the writers. 
Mus. Reg. No. 8219. 
*There is probably a slight mistake in referring this species to the **Magnesian limestone” of Drummond’s island, 
which belongs to the Upper Silurian. That limestone constitutes most of the island, and is not likely to hold its fossils 
in as éntire and perfect a condition as the specimen figured by Castelnau, However, there is a low exposure of the 
Lower Silurian along the north shore, rising about eighteen feet above the water, and these beds probably furnished 
the specimens deseribed by Castelnau. 
