420 MISSISSIPPIAN BRACHIOPODA 



Genus MART INI A McCoy 



Description. Shells usually of medium size or smaller, subcircular, 

 subovate or subelliptical in outline, the hinge-line short, the cardinal ex- 

 tremities rounded, the surface of the valves smooth or nearly so. The 

 pedicle valve with a small cardinal area whose lateral margins are not 

 sharply defirted, the surface curving with little or no differentation into 

 the lateral slopes of the valve, the delthyrium rather large; internally 

 neither dental lamella; nor median septum are present, the muscular scars 

 are small, scarcely impressed and ill-defined. In the brachial valve the 

 muscular scars are also inconspicuous, the crura and primary lamellae 

 of the brachidium are elongate, the bases of the spiral coils are situated 

 well forward and their apices are directed towards the cardinal ex- 

 tremities. 



Remarks. In general external form and in the smoothness of the shell 

 the members of this genus resemble some of the athyroid genera, but they 

 always possess a distinct cardinal area, although it is small, with a rather 

 large, open delthyrium. Waagen 1 has pointed out the presence of a min- 

 utely punctate structure in the epidermal layer of the shells of this genus, 

 a structure which does not penetrate the inner layers of the shell, and 

 considers it as one of the generic characters. This feature, how r ever, has 

 not been observed in any of the American shells which have come under 

 observation, a fact which may be due to the destruction of the epidermal 

 layer of the specimens observed. 



MARTINIA CONTRACTA (Meek and Worthen) 

 Plate LXXV, Figs. 1-10 



1861. Spirifera glabra var. contracta Meek and Worthen, Proc. Acad. Nat. 



Sci. Phil., p. 143. 

 1866. Spirifer glaber var. contractus Meek and Worthen, Geol. Surv. 111., 



vol. 2, p. 298, pi. 23, figs. 5a-b. 

 1888. Spirifer glaber Herrick, Bull. Sci. Lab. Denison, Univ. vol. 4, pi. 11, 



fig. 15. 

 1891. Spirifer (Martinia) contractus Whitfield, Ann. N. Y. Acad. Sci., 



vol. 5, p. 583, pi. 13, figs. 17-19. 



1894. Spirifera contracta Keyes, Mo. Geol. Surv., vol. 5, p. 83. 



1895. Spirifera (Martinia) contracta Whitfield, Geol. Surv. Ohio, vol. 7, 



p. 471, pi. 9, figs. 17-19. 

 1909. Martinia contracta Bassler, Va, Geol. Surv., Bull. No. II A, pi. 29, 



fig. 11. 

 1911. Martinia contracta Morse, Proc. Ohio State Acad. Sci., vol. 5, p. 375, 



figs. lOa-c. 



Description. Shell subovate or ovate-subquadrangular in outline, 

 longer than wide or with the length and width subequal, hinge-line short, 



iMem. Geol. Surv. India, ser. 13, pt. 1, p. 529. (1882.) 



