406 DEAKE — THE GEOLOGY OF INDIAN TEKRITORY. [Sept. 3, 



not distinctly set off from the rest of the shell, but differs from it 

 in ornamentation, so as to be well marked. 



The surface is marked by distinct radial ribs, somewhat narrower 

 than the interspaces. These ribs are often dichotomous, and also 

 increase by intercalation. Near the beak the surface is faintly 

 ornamented with distinct concentric striae of growth, which grow 

 stronger towards the posterior margin. The ears are ornamented 

 just as the rest of the shell, except that the ribs are somewhat 

 coarser on both anterior and posterior ears. 



A. rectilaierarius resembles very closely A. papyraceics Sowerby 

 of the European "Coal Measures, and indeed a more perfect suite of 

 specimens may show their identity, for many of the species that 

 accompany A. papyraceus in Europe have already been found in 

 America. 



Horizon and Locality. — Upper Coal Measures, Poteau group, in 

 the shales overlying the Mayberry coal, at the mines four miles 

 northwest of Poteau, Indian Territory. 



Schizodtts insignis sp. nov. Drake. PI. IX, Fig. 7. 



This species, one of the largest of the genus Schizodus, is repre- 

 sented in the collection only by a cast, so that the generic refer- 

 ence is not beyond doubt. The shell is large, being two and a half 

 inches in length and two inches in height. Convexity of the 

 valve is eleven-twentieths of an inch. The beak is rather high and 

 pointed, rising two-fifths of an inch above the hinge line. The 

 anterior margin is rounded, the posterior is broken off. The ante- 

 rior and posterior adductor impressions are quite large and distinct. 

 The cast is smooth, so nothing is known of the sculpture of the 

 surface. The only species with which Schizodus insignis may be 

 compared is Schizodus {Leptodomus') magnus Worthen, Geol. Surv. 

 III., Vol. viii, p. 107, PL XVIII, Fig. 2, of the Lower Carboniferous, 

 Chester horizon ; but ^. magnus differs from S. insignis in the 

 elongation of the anterior part of the valve, also in the sharp high 

 ridge that runs from behind the beak obliquely to the rear of the 

 shell. Otherwise there is considerable similarity, and the two spe- 

 cies may very well belong to the same genus. 



Occurrefice and Horizcii. — In hard sandstone of the Permian 

 horizon, five miles east of McDermitt, Indian Territory; only a 

 single specimen was found. 



