BRACHIOPODA. 199 



Family Spiriferidae 

 Genus Delthyris Dalman 



Delthyris perlamellosus (Hall) 



Plate 50, figures 41-49. 

 Spirifer perlamellosa Hall, 1857, 10th Ann. Rept. N. Y r State Cab. Nat. Hist., p. 57, 



figs. 1-5. 

 Delthyris macroplcura Rogers (not Conrad), 1858, Geol. Penn., vol. II, pt. II, p. 825, 



fig. 643. 

 Spirifer perlamellosus Hall, 1859, Pal. N. Y., vol. Ill, p. 201, pi. XXVI, figs, la-i, k-p, 



r-t, 2a-g, 1861.1 



Description — "Shell trigonal or semi-circular, more or less extended on the hinge 

 line, the extremities varying from obtuse or rounded to extremely mucronate. Ventral 

 valve arcuate, the beak much extended beyond the opposite valve, and incurved at 

 the apex; sinus deep, gradually expanding, and produced in front into a linguiform 

 extension. Dorsal valve convex toward* the middle, the mesial elevation very promi- 

 nent, and the beak closely incurved against the area, or partially closing the foramen 

 of the ventral valve. Area moderately wide, frequently much expanded, and becoming 

 linear towards the extremities when the shell is much extended. Surface marked by 

 four to six strong and abruptly elevated plications on each side of the mesial sinus and 

 elevation, concentrically marked by strong imbricating lamellae, which are abruptly 

 arched in passing over the plications, giving an extreme roughness to the surface. In 

 well-preserved specimens, finer longitudinal striae mark the surface of these lamellae. 

 In ordinary specimens, the concentric lamellae are more closely arranged and more dis- 

 tinctly imbricate towards the margin; while near the beaks they are more distant, 

 and are scarcely imbricate." — Hall, 1859. 



Remarks — The Missouri specimens have 3 or 4 plications on each side of the medial 

 fold and sinus. . 



Delthyris missouriensis n. sp. 



Plate 51, figures 1-11 



Description — This species differs from D. perlamellosus in that the ventral cardinal 

 area is perpendicular, or nearly so, to the plane of junction of the valves and is rela- 

 tively broader, and the beaks of the valves are of about equal height. 



The plications on each side of the medial fold and sinus vary from 3 to at least 6. 



Delthyris octocostatus (Hall)? 



Plate 51, figures 28, 29 

 Spirifer octocostatus Hall, 1857, 10th Ann. Rept. N. Y. State Cab. Nat. Hist., p. 62. 

 Spirifer octocostatus Hall, 1859, Pal. N. Y. f vol. Ill, p. 205, pi. XXVIII, figs. 4a-e, 1861. 

 Spirifer octocostatus Weller, 1903, Pal. N. J., vol. Ill, pi. 288, pi. XXX, figs. 5-8. 

 Spirifer octocostatus Maynard, 1913, Md. Geol. Surv., L. Dev., p. 401, pi. LXVIII, 



figs. 25-29. 



Description — "Shell subglobose; valves nearly equally convex. Ventral valve most 

 elevated near the beak; sinus angular, extending to the apex; beak slightly incurved. 

 Dorsal valve most convex in the middle; mesial elevation not prominent; beak rising 

 little above the hinge line, slightly incurved; hinge line less than the width of the shell, 

 rounded at the extremities. Area triangular, faintly defined, somewhat arcuate. Fora- 

 men narrow; a strong medium septum dividing the muscular area, and extending to 

 the apex of the foramen. Surface having about four rounded moderately prominent 



•Partial bibliography. 



