446 THE PALEONTOLOGY OF MINNESOTA. 
[Orthis (DaliuanellaJ subaMjuata. 
1879, Orthis jugosa James. The Palaeontologist, No 4, p. 31. 
1892. Dalmanella meeki Hall. Palaeontology of New York, vol. viii, pt. i. pp. 206, 224, pi. vc, flg. 3. 
1892. Orthis corpulenta Sardesox. Bulletin of the Minnesota Academy of Natural Sciences, 
vol. ili, p. 330, pi. V, flgs. 8-10. 
This variety is restricted to the upper portion of the Hudson River group and can 
be distinguished from 0. testudinaria Dalman by the following characters: Attains 
a larger size; valves thicker and more convex; cardinal areas wider and shorter; 
striae coarser in all stages of growth, with a larger number terminating on the 
cardinal lines; in the dorsal valve the muscular scars are more distinctly defined 
and often much thickened and elevated around the jnargin. 
Formation and locality. — In the Hudson River group at Spring Valley, Minnesota, this variety 
occurs in great numbers; also in the upper portion of the same formation at Oxford. Clarksville and 
elsewhere in Ohio. 
Collectors. — W. H. Scofleld, E. O. Ulrich and the writers. Also in the collection of Dr. C. H. 
Robbins, of Wykofl, Minnesota. 
Mus. Reg. Nos. 231, 236, 272, 4078-7985. 
Orthis (Dalmanella) subjsquata Conrad. 
PLATE XXXIir, FIGS. 30-36. 
1843. Orthis subcequata CoNRAD Proceedings of the Academy of Natural Sciences of Philadelphia, 
vol. i, p. 333. 
1847. Orthis subccquata Hall. Palaeontology of New York, vol. i, p. 118, pi. xxxii, flg. 2. 
1862. Orthis suhaquata Hall. Geology of Wisconsin, vol. i, p. 42, flgs. 1-3, and p. 436. 
1880. Orthis minneapolis N. H. Winchell. Eighth Annual Report of the Geological and Natural 
History Survey of Minnesota, p. 63. 
1883. Orthis perveta Hall. Second Ann. Kept., N.Y. State Geologist, pi. xxxiv, tigs. (?16,) 17, 18. 
1883. Orthis subcequata Hall. Ibidem, pi. xxxiv, flgs. 19-24. 
1892. Dalmanella suboequata Hall. Palaaontology of New York, vol. viii, pt. i, pp. IW, 207, 224, 
pi. vc. flgs. 6-11. 
1892. Dalmanella perveta Hall. Ibidem, p. 224, pi. vC, flgs. 13, 14. 
Original description: "Semioval; valves ventricose, subequal; lesser valve with 
a slight subangulated mesial furrow; larger valve prominent in the middle, with 
flattened sides; radiating striae fine, closely arranged, unequal, rounded; cardinal 
area rather wide; apex of large valve prominent, not profoundly elevated above the 
opposite beak; the dorsal margin concave. Length, half an inch." 
Adult shells vary considerably in size; biconvex, sometimes as wide as long, but 
generally attaining a greater breadth than length. In very young examples the 
hinge-line is as long as the greatest width; while in large and obese individuals it is 
only three-fifths of the breadth. Cardinal angles varying from acute to subacute 
and sometimes slightly rounded; lateral and anterior margins broadly and evenly 
rounding, the latter usually broadly, but slightly, deflected dorsally. 
Surface with fine striae, tubulose, bifurcating about twice. In the ventral valve 
they are less numerous down the middle, but increase in size and have, at varying 
intervals, very oblique, large op3aings. At the bise of these psrforation? the stria^ 
