440 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
CHAULISTOMELLA MUNDULA Cooper, new species 
Plate 67, D, figures 24-29; plate 76, C, figures 15-17 
Shell of large size for the genus, subrectangular in outline with the width 
slightly greater than the length; cardinal extremities forming an obtuse angle; 
sides oblique; anterior margin broadly rounded. Anterior commissure slightly 
uniplicate ; lateral commissure deflected slightly in a brachial direction at the 
posterior end. Surface multicostellate; costellae rounded, closely spaced, sepa- 
rated by striae narrower than the costellae; about 11 costellae in 5 mm. at the 
front margin. Concentric fila strong. 
Pedicle valve unevenly convex in lateral profile, the posterior half nearly flat, 
the anterior half gently depressed ; anterior profile very slightly convex ; umbonal 
region slightly convex and with an indistinct fold fairly definitely visible in the 
posterior third to half but barely perceptible or absent in the anterior half to 
two-thirds. Median and anterior regions slightly swollen, the median region 
slightly more convex than the anterior one; posterolateral extremities gently 
deflected toward the brachial ; interarea long, nearly catacline ; muscle scars deeply 
impressed, muscle field nearly equal in length and width; anterior indentation 
moderately deep ; adjustor scars fairly large ; pallial marks only lightly impressed. 
Brachial valve strongly convex in lateral profile with the greatest convexity in 
the posterior half; anterior half flattened. Anterior profile strongly convex with 
top somewhat flattened and short but steep lateral slopes. Umbo gently swollen, 
faintly sulcate; sulcus fairly distinct in the median region but not reaching the 
anterior margin; median region strongly swollen with steep anterior and lateral 
slopes. Interarea long, apsacline. 
Measurements in mm.— 
Brachial Hinge 
width 
sength length Width Thickness 
Foloty pest. |ccck Meee. aaa 23.4 25.0 27.0 23.1 T7, 
Paratype (117000h) ........ 26.9 27.2 30.1 25.8 12.3 
Types.—Holotype: 1170002 ; figured paratypes : 110442a,b, 117000e ; unfigured 
paratypes : 117000b-d,f-h. 
Horizon and locality—Bromide formation (Mountain Lake member) in Okla- 
homa: In the east side of the road cut on Oklahoma Highway 18, 1.8 miles south 
of Sulphur, Murray County ; deep well on Jones farm, sec. 22, T. 5 N., R.3 E, 
Pottawatomie County, 3,240 to 3,244 feet, Midcontinent Petroleum Corporation 
well. 
Discussion—This species is characterized by its subquadrate appearance, 
strongly rounded sides, narrow hinge, and robust form. Its contours are simi- 
lar to those of C. quadrata but differ in the greater convexity of both valves and 
the much larger size attained. 
A pedicle and brachial valve from a deep well in Pottawatomie County is re- 
ferred here. The pedicle valve agrees fairly well, but the brachial valve is some- 
what wider proportionally than is usual in the species. 
