NO. 4 



CRETACEOUS BRACHIOPODA, ARIZONA — COOPER 



and the descending lamellae are moderately broad and extend from the 

 crural processes anteriorly to join the median part of the curved lateral 

 plates at the distal end of the septum. The incision at the anterior end 

 is much deepened and the anterior ends of the broken loop ring are 

 beginning to diverge widely. 



No specimens between 6 and 12 mm. preserving good details of the 

 loop were taken from the acid residues. Specimens 12 mm. wide or 

 wider evidently have adult loops, but none of them are complete. The 

 lateral branches connecting the septum to the loop are broad, stout, and 

 long, frequently being strengthened by a median triangular plate. The 

 loop of an adult specimen 16.5 mm. wide (paratype U.S.N.M. No. 

 124220) has a broad transverse ribbon with long ears. 



MEASUREMENTS IN MILLIMETERS 



Types. — Holotype U.S.N.M. No. 124197a; figured paratypes 

 U.S.N.M. Nos. 124197b, d-j, 124198a, b, 124199, 124201a, b, 124220; 

 measured paratypes U.S.N.M, Nos. 124206 a-e; unfigured paratypes 

 U.S.N.M. Nos. 124197c, 124200a, b. 



Horizon mid locality. — Mural limestone, from a small hill 300 yards 

 east of U. S. Highway 80, NW^SWiNEi sec. 36, T. 23 S., 

 R. 25 E., Bisbee Quadrangle, Arizona ; Rancho Nuevo, 3 miles east of 

 Santa Rosalia, Sonora, Mexico, 



Discussion. — This species is characterized by having a low and in- 

 distinct fold and sulcus and differs from all other described species of 

 Genimarcula in this respect. This is the first report of the genus in 

 North America. Gemvwrcula arisonensis is about the same size as 

 G. aurea, type species of the genus, and has a cardinal process like it, 

 but the exterior is different as noted above. Genimarcula mcnardi 

 (Lamarck), a well-known species in France and Great Britain, is 

 larger than the American species and has a much more pronounced 

 fold and sulcus. It also differs from the Arizona shell in having a 

 more elaborate cardinal process. 



