BRACHIOPODA. 461 



nvty latlooatata.] 



This species is known in America as Rhynchonella increbescens Hall, but unfortun- 

 ately it must give way to E. intcquivalvis, 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 subatquata, 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, Chatfleld, 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. 

 Scofleld, 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 LATICOSTATA W. and 8. 



PLATE XXXIV, FIGS. 2fr-29. 



1892, April 1. Rhynchotrema incequivalvis, var. laticostata W. and S. American Geologist, vol. ix, 



p. 293. 

 1892, April 9. Rhynchonella sancta SAKDESON. Bulletin of the Minnesota Academy of Natural 



Sciences, vol. iii, p. 333, pi. iv, figs. 19-20. 



\ 



In the lower portion of the Galena south of Cannon Falls R. incequivalvis 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 diver sa Shaler that the 

 variety becomes common and attracts attention. In the Trenton of New York and 

 Kentucky an occasional specimen is found which approaches var. laticostata, but none 

 of them is so strongly transverse as Minnesota individuals. 



Collectors. W. H. Scofleld and the writers. 

 Mus. Reg. No. 8219. 



tThere Is probably a Might mistake in referring this spi-i MC-, to tin- "Hagnealan limestone" of Drummond's Island, 

 which belongs to the Upper Silurian. That limestone constitutes most of the Island, and is not likely to hold Us fossils 

 in as entire and perfect a condition :is I he specimen figured by Castelnau. However, there is a low exposure of the 

 Lower Silurian along the north shore, rising about eighteen feel above the water, and these beds probably furnished 

 the specimens described by Oastelnan. 



