CARBONIFEROUS SPECIES. ' 63 



Genus ORTHIS, Dalman. 

 Orthis Michelini, L'Eveill6, var. 



Plate 7, figs. 1, 1 a, 1 6, 1 c. 



Terebratula Michelini, L'Eveill6 (1835), M6m. Soc. G6ol. France, II, 39, pi. ii, figs. 14-17. 



Orthis Michelini, De Koninck (1843), An. Foss. Garb. Belg., 228, pi. xiii, figs. 8 and 

 10 c, d. — De Verneuil and De Keyserling (1845), Geol. Russ., II, 185, pi. xii, 

 fig. 7.— Semenow (1854), Foss. Schles. Kolenk., tab. iii, fig. 11.— McCoy (1854), 

 Brit. Pal. Foss., 448, tab. iii, fig. 11. — Davidson (18G0), Scottivsh Carb. Brach., 

 30, pi. i, figs. 7-10 ; and again (1861), Brit. Carb. Brach., 132, pi. xxx, figs. 6-12. 



Terebratula filiaria, Phillips (1836), Geol. Yorks., II, 220, pi. xi, fig. 3. 



Orthis divaricata, McCoy (1854), Synop. Carb. Foss. Ireland, pi. xx, fig. 17. 



Orthis eircularis, McCoy (1854), ib., fig. 17. 



Orthis Michelini var. Burlingtonensis, Hall (1858), Iowa Report, I, part ii, 596, pi. xii, 

 fig. 4. 



Compare Orthis Penniana, Derby (1874), Bulletin Cornell University, I, No. 2, 26. 



Shell rather gibbous, both valves being convex, but the ventral less 

 so than the dorsal, longitudinally oblong or subquadrate in outline, with 

 breadth nearly as great posteriorly as in front; lateral margins nearly straight 

 and parallel, anterior lateral rounding more or less abruptly into the front, 

 which is rounded, somewhat straightened, or very faintly sinuous near 

 the middle ; hinge-line very short, or less than one-third the breadth of 

 the valves. Dorsal valve distinctly and generally evenly convex; beak 

 slightly prominent, and only a little incurved ; area small, very moderately 

 arched. Ventral valve moderately convex all over, excepting near the front, 

 where it is depressed so as to form a broad, shallow, undefined, mesial 

 sinus ; beak projecting little beyond that of the other valve, and arched but 

 not strongly incurved ; area very small, well defined, inclined, and arching 

 more or less backward ; foramen moderate, but nearly or quite closed by the 

 cardinal process of the other valve. Surface of both valves ornamented by 

 numerous, crowded, even, more or less dichotomous, radiating striae, that arch 

 outward on the posterior lateral regions, and are crossed toward the front 

 and lateral margins by rather distinct marks of growth. (Internal charac- 

 ters unknown.) 



Length of largest specimen seen, 1.54 inches; breadth, 1.32 inches; 

 convexity, 0.95 inch. 



I have long been much perplexed in regard to the proper disposition 



