290 The American Geologist. May, 1892 
concave, with a broad delthyrium, which is occupied in part 
by a striated cardinal process. 
Plate xxxu, figs. 39-42. 
Formation and locality. Top of the Trenton shales at St. Paul, in 
association with 0. pectinella and variety sweeneyi. Cannon Falls, Ken- 
yon, Fountain, and elsewhere in Minnesota; Neenah and Oshkosh, Wis.; 
McGregor, Iowa. 
Orthis meedsi var. germana. 
This variety is ditferentiated from the above species by the fol- 
lowing characters: Smaller in size and squarer in outline; valves 
more strongly and evenly convex: hinge-areas nearly equally wide 
but narrower, with the beak of the pedicle valve slightly elevated 
beyond that of the brachial; pedicle valve with a slight, some- 
what angulated fold, while the brachial; has a shallow but dis- 
tinct sinus which originates immediately below the apex of the 
valve. These produce a slight sinuosity in the anterior margin, 
the direction of which is the reverse of that in O. meedsz. 
Plate xxxui, figs. 48-45. 
Formation and locality. Not rare in the Galena formation at a horizon 
which is about 30 feet above strata holding Clitambonites diversa at several 
localities south of Cannon Falls, near Kenyon and Fountain. 
Orthis proavita. 
Shell of medium size; subquadrate; hinge line equal to, or a 
little less than the greatest width of the shell; cardinal angles 
rounded or rectangular; sides gently convex and converging to a 
more or less flattened or slightly concave anterior margin.  Sur- 
face marked by simple, sub-angular strie having their origin at 
the apex of the valves or immediately below it, addition taking 
place by interpolation on the brachial and bifurcation on the ped- 
? 
icle valve; one to three striz terminating on the cardinal margin 
on each side of the umbo; 36 to 42 in number on mature exam- 
ples, crossed by a variable number of imbricating growth lines 
near the anterior margin. In some of the specimens the anterior 
margin is sharply reflexed as by old age. 
Pedicle valve has an insignificant mesial elevation. Area com- 
paratively narrow; delthyrium broad, triangular, two-thirds oc- 
cupied by the cardinal process of the other valve; beak somewhat 
incurved. Interior characters as in O, subquadrata. 
Brachial valve more or less strongly convex, greatest elevation 
