PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 637 
Discussion.—This is a small species distinguished by the pronounced sulcate 
brachial umbo and the depression of the median 2 costae below the level of the 
outer 2 in the fold. The species may be related to R. pristina but is generally 
smaller and proportionately more convex. It differs from R. orientalis, which is 
a small shell, in the nature of the folding and the more compact outline and profile. 
ROSTRICELLULA CUNEATA Cooper, new species 
Plate 124, H, figures 44, 45 
Shell small for the genus, cuneate, longer than wide; beak acute; sides nearly 
straight, divergent; anterior truncated. Surface marked by 11 narrowly rounded 
and elevated costae. 
Pedicle valve gently convex in lateral profile except for the front which is 
narrowly rounded; anterior profile moderately broadly rounded. Umbonal region 
narrowly rounded ; median region somewhat carinated by the prominent median 
costa. Median 3 or 5 costae elevated slightly in the anterior half to form a low 
fold; sides rounded and steep. Dental plates long and slightly curved. 
Brachial valve gently convex in lateral profile except for the front marginal 
region which is narrowly curved toward the pedicle valve; anterior profile flat- 
tened to concave medianly but with narrowly rounded sides. Sulcus originating 
at the umbo and extending to the anterior margin. Median 2 to 4 costae bound- 
ing median sulcus depressed below the flanks to form a broad sulcate zone; flanks 
narrowly rounded and with nearly vertical sides, marked by 3 to 4 costae. 
Median septum long. 
Measurements in mmn.— 
Brachial Widest 
Length length Midwidth part Thickness 
ERE Ose nisi aici n Si 4.0 a7 3.0 3.4 25 
Paratype (117218b)..... SG) Br 2.5 3.1 1.8 
a (TPVA18E yD: 4.8 rp 3 4.0 1.5 
Types.—Holotype: 117218a; unfigured paratypes: 117218b-d. 
Horizon and locality —Bromide formation (Mountain Lake member) in Okla- 
homa: West side U. S. Highway 77, sec. 25, T. 2 S., R. 1 E., 2 to 3 miles north 
of Springer, Carter County. 
Discussion.—This species strongly resembles members of the genera Spheno- 
treta and Dorytreta, but the presence of the thick median septum in the brachial 
valve indicates affinities with Rostricellula. This species suggests young speci- 
mens of R. costata, but in that species the brachial valve is less sulcate than 
R. cuneata. 
ROSTRICELLULA CUNEIFORMIS (Fenton and Fenton) 
Plate 136, A, figures 1-22 
Rhynchotrema cuneiformis FENTON and Fenton, Proc. Iowa Acad. Sci. for 1922, vol. 20, 
p. 72, pl. 1, figs. 12-14, 1924. 
Silicified specimens of this species show the interior to perfection. In the 
pedicle valve the deep delthyrial cavity is occupied by a thickened pedicle callist 
