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 O. chromatica, it will be necessary 
to accord recognition to the term Dioellomus, which, however, may be held in 
abeyance until that time. There 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 ? ^ 
complexus of Barrande,! from the Etage D, apparently a 
genuine Obolella, in a later fauna than has been elsewhere observed. 
Genus LEPT OBOLUS, Hall. 1871. 
PLATE III, FIGS. 1-10. 
1871. Leptoholus, 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. State Mus. Nat. Hist., p. 226, pi. vii, figs. 17-20. 
1875. Leptoholus, 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, Leptoholus lepis, Hall, Hudson group, loc. cit., p. 226, pi. vii, figs. 
1-9, 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. dec russ.-kais. Mineral. Gesellsch. zu St. Petersb., 2te Ser., Bd. iv. taf. xvii, fig. 1. 1868. 
t Syst&me Silurien Boheme, vol. v, pi. 152, fig. ii, 4; also, pi. 95, fig. iii; pi. Ill, fig. vi; pi. 113, fig. v. 
