BRACHIOPODA. 73 



substance of the shell is friable and chalky, and the sandstone so loose-grained 

 that internal impressions are not distinctly retained. Should future study of 

 the species prove it generically distinct from 0. chromatica, it will be necessary 

 to accord recognition to tlie term Dk'Ellomus, wliich, however, may ))e lield in 

 abeyance until that time. Tliere is a noticeable similarity in the interior of the 

 pedicle-valve of 0. polita as shown in fig. 38, to the illustration given by Vol- 

 BORTH of the interior of the corresponding valve in the species Schmidtia celata* 

 in which all the details represented are the two strong cen- 

 tral scars abutting against a thickened posterior area. The 

 correspondence in internal markings does not appear to ex- 

 tend to the brachial valves. (See discussion of the genus, 

 Schmidtia.) Attention may also be directed to the Obolus? 



^ ■' Fig. 31. Ololus ? complexus. 



complexus of Barrande,! from the Etage D, apparently a After jiAURANDB. 

 genuine Obolella, in a later faima than has been elsewhere observed. 



Genus LEPT OBOLUS, Hall. 1871. 



I'l.ATE in, FIGS. 1-10. 



1871. Leptoholits, Hall. Descriptions New Species Fossils, p. 3 ; Advance sheets Twenty-fourth Rept. 



N. Y. State Mus. Nat. Hist. 



1872. Leptoholus, Hall. Twenty-fourth Rept. N. Y. St.ate Mus. Nat. Hist., p. 226, pi. vii, figs. 17-20. 

 1875. Lept.oholiis, Hall and Whitfield. Palaeontology of Ohio, vol. ii, p. 69, pi. i, figs. 10, 11. 



Diagnosis " Shell semiphosphatic, fragile, minute, more or less elliptical, 

 ovate or subcircular, with moderately (or sometimes more extremely) convex 

 valves, which are concentrically marked on the exterior surface. Ventral 

 valve with a distinct pedicle-groove; interior with an elevated subquadrate 

 muscular area. Dorsal valve a little thickened on the cardinal margin, with 

 slightly elevated, trifid muscular impressions," Hall (loc. cit.). 



Type, Leptobolus lepis, Hall, Hudson group, loc. cit., p. 226, pi. vii, figs. 

 19, 20. 

 L. occidens, Hall, Hudson group, loc. cit, p. 227, pi. vii, fig. 18. 

 L. insignis, Hall, Utica slate, loc. cit, p. 227, pi. vii, fig. 17. 



* Verhandl. der russ.-kais. Mineral. Gesells<:h. zu St. Petersb., 2te Ser., Bd. iv. taf. xvii, fig. 1. 186S. 

 t SystJme Silurien Boheme, vol. v, pi. 152, fig. ii, 4; also, pi. 95, fig. iii ; pi. Ill, tig. vi ; pi. 113, fig. v. 



