PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 389 
and sides long and gentle. Median costa slightly depressed below those surround- 
ing it. Palintrope strongly apsacline to nearly procline; interarea nearly flat. 
Brachial valve moderately convex in lateral profile, more so than the pedicle 
valve ; anterior profile broadly convex with a depressed median area correspond- 
ing to the sulcus. Umbonal region sulcate; sulcus deep at the umbo, widening 
and becoming more shallow anteriorly to occupy approximately half the width 
at the front margin. Sulcus occupied by 2 costae; space between the 2 costae 
forming the deepest part of the sulcus and corresponding to the median costa of 
the pedicle valve. Flanks moderately convex, fairly broad. Slopes to cardinal 
extremities concave, short and steep. 
Measurements in mm.— 
Dorsal Hinge 
Length length Width width Thickness 
Holotype (pedicle valve) ......... 2.6 ? 4.8 4.3 1.0? 
Paratype (brachial valve 110095a). ? ay 5.5 5.2? 0.8 ? 
Types.—Holotype : 110095b; figured paratype: 110095a; unfigured paratypes: 
I10095c-e. 
Horizon and locality—McLish formation in Oklahoma: Section along and 
west of U.S. Highway 77, sec. 25, T. 2 S., R. 1 E., 2 to 3 miles north of Springer, 
Carter County. 
Discussion.—This little species has the form and size of P. lamellosum but 
differs in not possessing the deep sulcus of the pedicle valve which is a conspicu- 
ous feature of the New York shell. The Oklahoma species has less costae than 
the New York shell. 
PTYCHOPLEURELLA PORCIA (Billings) 
Plate 42, B, figures 10, 11 
Orthis porcia Bitit1ncs, Canadian Nat. Geol., vol. 4, p. 439, figs. 16-18, 1859; Geol. Canada, 
p. 130, fig. 58, 1863. 
Clitambonites porcia (Billings) RAymMonp, Ann. Carnegie Mus., vol. 7, No. 2, p. 248, pl. 36, 
figs. 15, 16, IQII. 
This is a small species, finely multicostellate and finely imbricate. The lateral 
margins are gently rounded and the cardinal angles obtuse. Interarea orthocline ; 
delthyrium very narrow. This species has the external features of Ptychopleurella 
rather than Clitambonites. Raymond states that it has a narrower “deltidium” 
and spondylium than Clitambonites multicostus. However, examination of the 
type specimen indicates that no deltidium is present and that the spondylium is 
not visible. 
Types—Holotypes: G.S.C. 1044. 
Horizon and locality —St. Martin formation, Island of Montreal, Quebec, 
Canada. 
PTYCHOPLEURELLA RECTANGULATA Cooper, new species 
Plate 42, D, figures 13-21 
Shell small, subrectangular in outline ; hinge slightly narrower than the great- 
est shell width; cardinal extremities obtuse; sides rounded; anterior margin 
