NO. 4 CRETACEOUS BRACHIOPODA, ARIZONA — COOPER 5 



Pedicle valve moderately convex in lateral profile and with the 

 maximum convexity at about the middle ; anterior profile fairly 

 strongly convex ; umbonal region narrowly convex to subcarinate, the 

 narrow swelling continued nearly to the median region where it dies 

 out. Anterior third flattened to faintly sulcate. Beak erect, obliquely 

 truncated ; foramen broadly elongate, moderately large, oval to circu- 

 lar, submesothyrid to mesothyrid. Deltidial plates conjunct, not 

 covered by beak, suture visible. Beak ridges strong. 



Interior of pedicle valve with large and thick teeth; dental plates 

 obsolete ; pedicle collar small. Muscle marks too indistinct to discern 

 individual scars or pattern of field. 



Brachial valve shallow, gently convex in lateral profile and broadly 

 convex in anterior profile ; umbonal region gently swollen ; beak ob- 

 scured by the overlapping of the deltidial plates ; median region gently 

 swollen and forming a barely perceptible fold which appears at the 

 front margin as a gentle wave of the commissure in the direction of 

 the brachial valve ; flanks gently inflated and with short, steep sides. 



Interior with short stout loop having short crura and short blunt 

 crural processes ; descending lamellae short ; transverse ribbon broad 

 in adults, fairly strongly elevated and with a flattened crest at its 

 middle; outer socket plate moderately broad, moderately concave; 

 inner socket plates nonexistant to small ; inner socket ridge strong, 

 overlapping the teeth. Cardinal process small, wide and short. Muscu- 

 lature and pallial marks poorly impressed, elongate, somewhat tear- 

 shaped. 



MEASUREMENTS IN MILLIMETERS 



Brachial 



Length length Width Thickness 



Holotype U.S.N. M. No. 124194b 17.6 14.0 14.0 9.4 



Paratype U.S.N.M. No. 124194a 16.9 13.9 12.5 8.8 



" 124194c 20.3 17.4 17.4 11.6 



" I24i94d 54 4-7 3-9 2.7 



" " " I24i94e 11.4 9.2 8.9 5.2 



Types. — Holotype U.S.N.M. No. 124194b; figured paratypes 

 U.S.N.M. Nos. 124187, 124188, 124194c, d, 124195, 124195a, 124196c; 

 unfigured paratypes U.S.N.M. Nos. 124194a, e, 124196a, b, 124205, 

 I 242 I 8. 



Discussion. — This species is characterized by the unequal convexity 

 of the valves, the suberect to erect beak (Thomson classification, 

 1927), rectimarginate to faintly plicate anterior commissure, and short, 

 stout loop. I am not completely happy about the assignment of this 



