382 THE PALEONTOLOGY OF MINNESOTA. 
[Pentameridae. 
line is longer, and the cardinal area of the ventral valve is wider, as compared with 
that species, while a more conspicuous mesial sinus and fold are present in S. anthon- 
ensis. Further in the apical portion of the delthyrium there is a small spondylium, 
and in the dorsal valve the space between the crural plates is thickened by shell 
deposit and is medially divided by a sharp, but low, cardinal process, the whole being 
drawn out into a long, angular, medial septum. 
Formation and- locality. — Eare in the Trenton limestone and shales at Minneapolis, St. Paul and 
near Cannon Falls, Minnesota. In the Trenton at Dixon, Illinois. Common in the "Glade limestone'' 
at Lebanon, Tennessee. 
Collectors.— E. O. Ulrich, W. H. Scofleld and C. Schuchert. 
Mus. Reg. No. 8252. 
Family PENTAMERIDAE, McCoy. 
Genus ANASTROPHIA. Hall. 
AnASTROPHIA ? HEMIPLICATA HttlL Sp. 
PLATE XXX, FIGS. 29-:il. 
1847. Atrypa hemiplicata Hall. Palaeontology of New York, vol. i, p. 144, pl.xxxin, flg. 10. 
1856. Atrypa hemiplicata Billings. Canadian Naturalist and Geologist, vol. i, p. 208, flgs. 20-23. 
1859. Pentamerus hemiplicatus Billings. Canadian Journal, vol. iv, p. 316. 
1859. Pentamerus hemiplicatus Hall. Twelfth Report N. Y. StateCabinet of Natural History, p. 66 
1863. Camarella hemiplicata Billings. Geology of Canada, p. 168, tig. 154. 
1892. Camarella bernensis Saudeson. Bulletin of the Minnesota Academy of Natural Sciences, 
vol. iii, p. 328, pi. iv, flgs. 4-6. 
Original description: '* Subglobose, pentagonal, wider than long, thickness often 
equal to the length; cardinal line distinct, short, with (in some specimens) the 
appearance of a small area on the dorsal [ventral] valve; dorsal [ventral] valve 
depressed-convex, with an abrupt, broad, not deep sinus, which commences nearly 
half way from the beak to the base, the beak very small and closely incurved [with 
a small triangular delthyrium underneath]; ventral [dorsal] valve very convex, 
becoming gibbous with a broad mesial elevation, commencing one-third of the dis- 
tance from beak to base, more gibbous towards the beak; sinus marked by two or 
three strong plications, with three or four upon the mesial lobe, and two or three 
on each side, all of which reach from one third to one-half the distance from 
the base to the beak of the shell, leaving the upper half entirely free from these 
markings; entire surface ornamented by fine, concentric, filiform, subimbri^ating 
lines, which are more conspicuous towards the base of the shell and beautifully 
undulated in crossing the plications." 
In Minnesota this species occurs not uncommonly near the base of the Galena 
and differs from New York examples in having the umbo of the dorsal valve more 
tumid and elevated beyond that of the ventral valve. The transverse diameter in 
the former is also shorter, while the individuals are commonly smaller than thjse 
from eastern localities. 
