NO, 4 CRETACEOUS BRACHIOPODA, ARIZONA — COOPER 7 



specimen during the etching and was not recovered. Unfortunately 

 the loop is thus revealed from the dorsal side which is not the most 

 advantageous view for appreciation of the structure. 



The loop is of the normal size as shown by other specimens. The 

 descending branch is very stout and the transverse band is strong and 

 thick. The crural processes appear to have been normal but the points 

 grew inward and united to form a transverse band, thinner than the 

 anterior one but with the band convex toward the pedicle valve and 

 having a form like that of the normal ribbon. 



GEMMARCULA ARIZONENSIS Cooper, new species 

 Plate 2A, figures 1-28; plate 4B, figures 3-6 



Shell small, attaining a width of slightly more than one-half inch, 

 transversely elliptical in outline ; wider than long and with a narrow 

 hinge. Widest at about the middle. Sides rounded ; anterior margin 

 subnasute to broadly rounded ; anterior commissure rectimarginate to 

 faintly uniplicate, the uniplication clearly visible only in old specimens. 

 Valves unequal in depth, the pedicle valve having the greater depth. 

 Surface multicostate, the costae appearing in three generations. Costae 

 numbering 20 to 24 on the front margin of an average adult. 



Pedicle valve moderately to strongly convex in lateral profile and 

 broadly to strongly convex in anterior profile, the convexity in both 

 profiles depending upon age. Umbo somewhat narrowly convex, the 

 convexity continued anteriorly as an indistinct fold which is bounded 

 somewhat indistinctly by two costae stronger than those surrounding 

 them ; median region swollen ; flanks and anterior slope steep. Beak 

 irregular from pedicle pressure against rough surface ; interarea wide 

 and long; foramen large and circular; deltidial plates disjunct in the 

 young, conjunct in old specimens and forming a symphytium. 



Interior of the pedicle valve with short but stout dental plates, 

 strong transverse teeth ; callosity of pedicle collar on floor of delthy- 

 rial cavity thick ; median septum low, extending anteriorly to beyond 

 the valve middle. 



Brachial valve gently to moderately convex in lateral profile, broadly 

 but gently convex in anterior profile; umbo gently convex, often 

 abraded by pedicle pressure against the substratum. Fold barely per- 

 ceptible except in old specimens, and usually defined by a median 

 crowding and smaller size of the costellae. Flanks gently swollen and 

 with long, gentle slopes to the margins. 



Interior of the brachial valve with a thick concave notothyrial cal- 

 losity buttressed by a strong median septum that extends to about the 



