BRACHIOPODA. 403 



Variety Inquassa. 



Formation and locality. Very common in the upper portion of the Trenton limestone at Minneapolis, 

 St. Paul, Cannon Falls and Fountain, Minnesota. Also abundant in the "Lower Blue beds" at Janesville 

 and Beloit, Wisconsin; Rockton, Illinois. Very rare in the Trenton shales at St. Paul and Cannon Falls, 

 Minnesota; Decorah and McGregor, Iowa. Also at Dixon, Illinois, in the Trenton; in the Birdseye lime- 

 stone at High Bridge, Kentucky, and in the "Glade limestone" at Lebanon, Tennessee. 



Collectors. C. L. Herrick, H. V. Winchell, Win. Howling, W. H. Scofleld and the writers. 



Mus. Reg. Nos. 671, 673-675, 681, 685. 704, 705, 2192, 3521-3523, 3731, 5059, 5097, 5673, 7919, 8143-8148. 



Variety INQUASSA Sardeson. 



PLATE XXXI, FIGS. 27. 28. 



1892, Strophomena inquassa SARDESON. . Bulletin of the Minnesota Academy of Natural Science, 



vol. iii, p. 334, pi. v, flgs. 22-24. 



This name is applied to large convex shells with a wide ventral hinge area 

 which otherwise strongly resemble R. alternata. In Minnesota specimens are rare. 

 They occur in the upper third of the Trenton shales and continue upward into the 

 Galena, passing into a very gibbose form, R. deltoidea Conrad. In Wisconsin variety 

 inquassa is quite abundant near the base of the "Upper Buff limestone " and has been 

 identified by Hall as Strophomena incrassata (op. cit., 1862). It is not always easy to 

 distinguish between R. minnesotensis, var. inquassa, R. deltoidea and R. alternata. This 

 is particularly the case between var. inquassa and the latter species when the exterior 

 alone is visible. The thickening of the shell, however, near the anterior margin on 

 the interior of the dorsal valve in R. alternata is much stronger, while the four ridges 

 of R. minnesotensis, var. inquassa, two on each side of the median septum, are reduced 

 to two in the former species. The tendency in the progressive line of development 

 from R. minnesotensis seems to be towards larger growth (var. inquassa) and greater 

 convexity (R. deltoidea), while another series tends to flatter shells and maximum of 

 size (R. alternata). 



Formation and locality. Rare in the Trenton shales at Minneapolis, St. Paul and elsewhere in 

 Minnesota. Common near the base of the " Upper Buff beds" at Mineral Point, Wisconsin. 



Mus. Reg. Nos. 8141. 



RAFINESQUINA DELTOIDEA Conrad, sp. 



PLATE XXXI. FIGS. 30 and 31. 



1839. Strophomena deltoidea CONRAD. Third Annual Report of the New York Geological Survey, 



p. 64; Fifth Report, p. 37, 1811. 



1842. Strophomena deltoidea VANUXEM. Geology of New York; Report Third District, p. 46, flg. 2. 

 1842. Strophomena deltoidea EIIMONS. Ibidem, Report Second District, p. 389, flg, 2. 

 1842. Strophomena camerata CONRAD. Journal of the Academy of Natural Sciences of Philadelphia, 



vol. viii, p. 254, pi. xiv, flg. 5. 



1847. Leptcena camerata HALL. Paleontology of New York, vol. i, p. 106, pi. xxxiA, flgs. 2a, 2b. 

 1847, Leptcena deltoidea HALL. Ibidem, p. 106, pi. XXXIA, flgs. 3a-3e. 

 1863. Strophomena deltoidea BILLINGS. Geology of Canada, p. 163, flg. 141. 

 1883. Streptorhynchus (Strophonella) deltoidea HALL. Second Annual Report N. Y. State Geologist, 



pi. XLII, flgs. 1, 2, 4 (not flg. 3). 

 1892. Raflnesquina deltoidea HALL. Paleontology of New York, vol. viii, pt. i, pi. ixA, flgs. 1, 2, 4. 



