968 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Horizon and locality.—Dark shale below the Eureka quartzite in Nevada: Be- 
low two knobs of the Eureka quartzite, north side canyon, 3.1 miles N. 32° E. 
of Blair (Segura) Ranch, Antelope Mountains, Roberts Mountains (1°) Quad- 
rangle. 
Discussion.—This species is characterized by its large size and fine costellae. 
The only other American Paurorthis approaching it is P. ponderosa from the 
Benbolt formation, but this does not attain the size of the western species. Fur- 
thermore, P. ponderosa has narrower fascicles and a more carinate pedicle valve 
than P. gigantea. 
PAURORTHIS LONGA Cooper, new species 
Plate 150, A, figures 1-16 
Small, subrectangular in outline, with the length and width about equal; great- 
est width at about the middle; sides nearly straight; anterolateral extremities 
narrowly rounded; anterior margin rounded. Hinge narrower than the greatest 
shell width. Anterior commissure sulcate. Surface fascicostellate. 
Pedicle valve gently convex in lateral profile; strongly convex in anterior 
profile and much deeper than the brachial valve; beak long, incurved; interarea 
curved, moderately apsacline. Umbo and median region swollen from beak to 
anterior margin and thus forming a fold; flanks gently inflated, steep. 
Brachial valve moderately convex in lateral profile and with the maximum 
depth in the posterior two-thirds; anterior third gradually geniculated toward 
the pedicle valve; anterior profile broadly convex, with middle slightly concave. 
Umbo and region immediately anterior to it strongly swollen; sulcus originating 
at the beak, broad and shallow. Flanks full and with moderately steep slopes. 
Interior of brachial valve with delthyrial cavity deep and long, dental plates 
nearly obsolete; median ridge well developed, usually narrow and extending 
nearly to the anterior margin. Delthyrium narrowed by lateral plates. 
Brachial interior with thick brachiophores, prominent median ridge, and deeply 
impressed adductor impressions. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
Hiplety pe |}: -wiseesai «6 8.3 72 7.7 6.6 5.4 
Paratype (117282a)..... ORG 6.9 7.6 6.2 5.1 
* (1972820) re 3% 8.4 TRE 8.1 6.7 5.0 
Types.—Holotype: 117282b; figured paratypes: 117282a,c,e-k, 117283d; un- 
figured paratypes: 117282d, 117283a-c,e. 
Horizon and locality—Lower part of Arline formation in Tennessee: 100 
yards southwest of the Negro Cemetery, 4 mile northeast of Friendsville ; + mile 
east-southeast of Friendsville ; north side wagon road in glade, + mile southeast 
of Friendsville; Concord (T.V.A. 138-SW) Quadrangle. 
Discussion.—This species is related to P. fasciculata but is distinguished by a 
thick shell and an elongate form. The sides are subparallel, and the fascicula- 
tion is less regular than in P. fasciculata. 
