Variety Inquassa. 
BRACHIOPODA. 
408 
Formation and locality.— Yery 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.— G. L. Herrick, H. V. Winchell, Wm. 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 Sakdeson. Bulletin of the Minnesota Academy of Natural Science, 
vol. iii, p. 334, pi. v, figs. 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 
Oalena, 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 XXXT. FIGS. 30 and 
1839. Strophomena deltoidea Conrad. Third Annual Report of the New York Geological Survey, 
p. 64; Fifth Report, p. 37, 1841. 
1842. Strophomena deltoidea Vanuxem. Geology of New York; Report Third District, p, 46. fig. 2. 
1842. Strophomena deltoidea Emmons. Ibidem, Report Second District, p. 389, fig. 2. 
1842. Strophomena camerata Conkad. Journal of the Academy of Natural Sciences of Philadelphia, 
vol. viii, p. 254, pi. xiv, fig. 5. 
1847. Leptaina camerata Hall. Palaeontology of New York, vol. i, p. 106, pi. xxxiA, figs. 2a, 2b. 
1847, Leptcena deltoidea Hall. Ibidem, p. 106, pi. xxxiA, figs. 3a-3e. 
1863. Strophomena deltoidea Billinos. Geology of Canada, p. 163, flg. 141. 
1883. Streptorhynchus {Strophonella) deltoidea HALL. Second Annual Report N. Y. State Geologist. 
pi. XLii, figs. 1, 2, 4 (not fig. 3). 
1892. Raflnesquina deltoidea Hall. Palaeontology of New York, vol. viii, pt. i, pi. ixA, flgs. 1,2. 4. 
