310 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Measurements in mm.— 
Brachial Hinge 
Length length Thickness Width width 
Holotype ois ee ate 7.0 6.3 3.0 7.0 6.8 
Paratype (109832a)..... 5.6 5.0 3.0 6.5 5.4 
7 (116871b)..... 7.5 6.7 4.0 acs 6.9 
‘é ( TTO8720)) eséhinse 6.9 6.4 212 8.1 7.9 
S (109832g)..... 5.0 48 3.0 5.8 5.2 
Types——Holotype: 116872a; figured paratypes: 109832a,b, 116871b, 
116872b,c; unfigured paratypes: 109832c-j, 116871Ia. 
Horizon and locality.—Benbolt formation in Virginia: Wash on east side slope 
in pasture, 0.2 mile south of middle fork of Moccasin Creek, 14 miles south of 
Hansonville, Hansonville (T.V.A. 205-SW) Quadrangle; west slope of the hill 
4 mile east of Cedar Point School, Hilton (T.V.A. 197-NW) Quadrangle. 
Effna formation in Virginia: At Porterfield Quarry, 5 miles east of Saltville, 
Maccrady (T.V.A. 218-NW) Quadrangle. 
Botetourt formation in Virginia: Opposite road intersection with Hays Creek, 
2 miles northwest of Brownsburg, Lexington (15’) Quadrangle; south side of 
the road, 0.2 mile east of Strasburg Junction, Strasburg (15’) Quadrangle. 
Chatham Hill formation in Virginia: 1.2 miles S. 31° E. of Sharon Springs, 
Burkes Garden (15’) Quadrangle. 
Discussion.—This species is characterized by its small size, strong angular 
costae and nearly equal length and width. As now constituted this is a variable 
species. The specimens from Porterfield Quarry are a little more strongly con- 
vex than the Benbolt specimens, and the internal structures are more neatly de- 
fined. The Benbolt specimens on the other hand have very thick dental plates 
and a thickened callosity anterior to the muscle area of the pedicle valve. The 
exterior impressions from northwest of Brownsburg show the concentric fila 
well. 
This species differs from O. blountensis in its more quadrate form and from 
O. bielsteini in its smaller size and quadrate form, although the number of costae 
is about the same for the two species. 
ORTHAMBONITES PAUCICOSTATUS (Ulrich and Cooper) 
Plate 33, D, figures 12-19 
Orthis paucicostata ULRicH and Cooper, Geol. Soc. Amer. Special Pap. 13, p. 103, pl. 15, C, 
figs. 16-21, 1938. 
Types.—Holotype: 92841; paratypes: 92842a-e ; figured hypotypes ; 1098342, 
b,m; unfigured hypotypes: 109834c-l. 
Horizon and locality—Upper Pogonip group (lower part of Rhysostrophia 
bed) in Nevada: Ikes Canyon, east side Toquima Range, Roberts Mountains 
(1°) Quadrangle. 
ORTHAMBONITES RECTANGULATUS Cooper, new species 
Plate 34, C, figures 10-15 
Shell rectangular in outline with the hinge equal to or slightly wider than the 
shell at the middle; sides gently rounded; anterior margin broadly rounded; 
