PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 971 
delthyrial cavity is often very strongly elevated, and a small median ridge extends 
anteriorly from it. The brachiophores of the brachial valve are unusually long, 
and some of them show crura extending from the anterior end on the side near- 
est the brachial valve. 
PAURORTHIS PARVA (Pander) 
Plate 151, D, figure 19 
The brachial interior of the European species is introduced for comparison 
with American shells. This is the type species of the genus. 
Figured specimen.—52314h. 
Horizon and locality—Walchow formation (BII), in Russia: Near Len- 
ingrad. 
PAURORTHIS PONDEROSA Cooper, new species 
Plate 146, E, figures 39-43; plate 149, G, figures 44-53; plate 151, F, figures 25-29 
Large for the genus, thick shelled, subcircular in outline; greatest width at the 
middle; cardinal extremities rounded; sides gently rounded; anterior margin 
somewhat narrowly rounded. Anterior commissure broadly and moderately 
deeply sulcate. Hinge width one-third less than the midwidth. Surface fascico- 
stellate, the fascicles best developed in the younger stages, flattening and dissolv- 
ing near the anterior margin. . 
Pedicle valve moderately convex in lateral profile, with the greatest convexity 
just anterior to the umbo; anterior profile strongly and somewhat narrowly con- 
vex and with long, steep lateral slopes. Pedicle valve deeper than the brachial 
valve. Beak long and incurved; interarea gently apsacline, curved. Umbonal 
and median regions narrowly swollen to form a fold with steep sides. 
Brachial valve in lateral profile most convex in the posterior two-thirds, some- 
what flattened in the anterior third. Anterior profile moderately and broadly 
convex and with a slight median depression. Umbonal region strongly swollen; 
beak prominent. Sulcus originating at the beak, shallow throughout its extent. 
Flanks gently inflated; slopes to the margins short, moderately steep. 
Interior of pedicle valve with deep and wide delthyrial cavity, deeply im- 
pressed vascula media separated by a narrow and low median ridge. Brachial 
interior with narrow and shallow notothyrial cavity and short, stout brachio- 
phores. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
TAGIGEVOR, sitiie wndtenttts GeOhD. Haida ses jes 13.7 12.4 13.6 10,2 9.3 
Paratype: ‘((1r7206a) 2348) ts Uy 7, 11.2 12.3 9.1 6.8 
Fs Gr17204b)-cwiiwils. usoateiaoct 12.2 bitea! II.9 0.9 7.4 
* (pedicle valve 117295a)..... 15.3 ? 15.7 BOW 910.7, 
= (brachial valve 117295b).... ? 15.1 15.6 10.2 3.6 
Types.—Holotype: 117294a; figured paratypes: 117293, 117294b, 117295a,b, 
117296a ; unfigured paratypes: 117296b. 
Horizon and locality—Sevier formation (near base) in Tennessee: On the 
