432 Systematic Paleontology 



dorsal adductor scars and cardinal structure." To the writer the Mary- 

 land material has the interior characters of Amboccelia but S. modestus is 

 different and of the lower part of the Keyser member. 



Occurrence. — Helderberg Formation, New Scotland Member. 

 Highest shale zone at 21st Bridge. 



Collection. — U. S. National Museum. 



Genus METAPLASIA Hall and Clarke ^ 



Metaplasia PYX idata (Hall) 

 Plate LXXII, Figs. 11, 12 



Spirifer pyxidatus Hall, 1859, Nat. Hist. N. Y., Pal., vol. iii, p. 428, pi. c, figs. 



9-12, 1861. 

 Metaplasia pyxidata Hall and Clarke, 1893, ibidem, vol. viii, pt. ii, p. 56, pi. 



xxxix, figs. 19-22. 



Description. — " Shell semielliptical in outline, one side ang-ularly 

 gibbous in the middle; cardinal line equalling (sometimes a little greater 

 or less than) the greatest width of the shell. Ventral valve with a narrow 

 mesial sinus, in the summit of a broad, strong elevation; the beak 

 abruptly incurved over a narrow linear area, which extends to the cardinal 

 extremities; foramen of moderate width, with strong divergent dental 

 lamellae. The muscular impressions are well marked, and sometimes there 

 is a thickened process from the interior filling the summit of the foramen. 

 Dorsal valve flat at the sides and near the beak, with a broad depression 

 below, in the center of which is a narrow mesial elevation. The margins 

 of the shell on each side present a few undulations or marginal folds, and, 

 in rare examples, these reach half way to the beak." Hall, 1859. 



The surface, in its perfect condition, has been very delicately con- 

 centrically striated, .s^lit'll substance fibrous and apparently impunctate. 



'At the time Hall and Clarke (Nat. Hist. N. Y., Pal., vol. viii, pt. ii, 1893, 

 p. 56) established this genus they had seen no specimens with calcified brachial 

 spirals and concluded that the general structure was suggestive of Orthis. 

 Recently a specimen of M. pyxidata was found by Mr. Roeder preserving the 

 spirals, and these have the general structure of the Spiriferidae. They are 

 postero-laterally directed, have seven volutions to each comparatively large 

 cone, and the descending lamellae are very wide and devoid of processes or 

 remnants of a connecting or transverse band. 



