PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 653 
in anterior profile. Sulcus originating about 5 mm. anterior to the beak, broad 
and shallow; tongue short, truncated. Flanks narrow and steep sided. 
Brachial valve slightly deeper than the pedicle valve, gently convex in lateral 
profile ; broadly convex in anterior profile and somewhat flattened in the middle; 
fold originating just posterior to the middle, flattened, not strongly elevated. 
Flanks narrowly rounded and steep sided. 
Measurements in mm.—Holotype, length 13.3, brachial length 11.8, width 15.8, 
thickness 9.6. 
Type.—Holotype :117231. 
Horizon and locality—Lebanon formation in Tennssee: On U. S. Highway 
41, $ mile south of Knox Branch, 9 miles southeast of Murfreesboro, Rutherford 
County. 
Discussion.—This species is characterized by its strong and distant costae and 
the marked truncation of the anterior end. It is most like R. angulata in its 
strong costation but differs in its anterior truncation and in having more numer- 
ous costae on the fold and in the sulcus. 
ROSTRICELLULA TUMIDULA Cooper, new species 
Plate 131, C, figures 17-27 
Shell large for the genus, subtriangular in outline; valves subequal in depth. 
Beak approximating a right angle; anterolateral extremities narrowly rounded ; 
anterior margin broadly rounded to nasute. Surface costate, sulcus occupied by 
5 to 7 narrowly rounded to subangular costae separated by spaces equal in width 
to the costae; fold marked by 6 to 8 costae and the flanks by 5 to 7 costae. 
Pedicle valve moderately convex in lateral profile, with the greatest convexity 
at about the middle; posterior third and umbonal region gently swollen; sulcus 
originating about 7.5 mm. anterior to the beak; sulcus broad and shallow, equal 
in width to more than half the width of the valve; tongue moderately long, 
broadly rounded. Flanks moderately rounded and with moderate slopes to the 
margins. 
Brachial valve fairly strongly convex in lateral profile and with the maximum 
curvatures at about the middle. Fold not strongly defined, originating about 
6 mm. anterior to the beak, gently rounded in anterior profile; only slightly ele- 
vated at the front. Flanks rounded in profile but with steep lateral slopes. Um- 
bonal and median regions swollen. 
Measurements in mm.— 
Brachial 
Length length Width Thickness 
Pipl type jatar ot diss’ l prep: aney 20.6 18.1 20.1 13.3 
Patatypey (o8to6a) 0.5... e6es 18.3 16.7 16.6 12.8 
+ CORIOGE) |S etl es sine ian 17.5 15.5 17.9 12.0 
Types.—Holotype: 98196b ; figured paratypes: 98196a,c. 
Horizon and locality—Dryden formation in Virginia: 4 mile west of Fullers 
Corner, I mile south-southeast of Big A Mountain, Big A Mountain (T.V.A. 
204-SE) Quadrangle. 
