BRACHIOPODA. 365 



SchizotretaJ 



The single specimen which is here referred, with some doubt, to this species is 

 a dorsal valve about 4 mm. in hight. The apex is nearly central, with the anterior 

 slope strongly convex, while the posterior slope is slightly concave. 



Formation and locality. From the Salmon River (Hudson River) group or Loraine shales near 

 Spring Valley, Minnesota. Also in the Trenton formation at Middleville and Lowville, New York; 

 Bellville and Ottawa, Canada. 



Collector. Charles Schuchert. 



Genus SCHIZOTRETA, Kutorga. 



1848. Schizotreta, KUTORGA. Verhandl. der russ. Kais. Mineral. -Gesellsch. zu St. Petersburg, 



pp. 272, 273. 

 1890. Schizotreta, HALL. Paleontology of New York, vol. viii, abstract, p. 135. 



This snbgenus is readily distinguished from Orbiculoidea "in having the perfor- 

 ated valve very convex and the imperf orate one depressed-conical or flat. 



" The pedicle-groove has essentially the character seen in OrUculodea, d'Orbigny, 

 but is usually much more distinctly retained on account of the greater thickness of 

 the shell. 



"Muscular impressions of the brachial or imperforate valve in Schizotreta conica 

 Dwight, consist of two strong excavated anterior adductors approaching toward the 

 center of the shell, and separated by a prominent septum which is continued from a 

 somewhat thickened posterior muscular area." (Hall, op. cit.) 



Interior of ventral valve with the posterior adductor scars situated on each side 

 of the walls of the pedicle groove. 



SCHIZOTBETA PELOPEA Billings, Sp. 

 PLATE XXIX, FIGS. 26-28. 



1862. Discina pelopea BILLINGS. Palasozoic Fossils, vol. i, p. 52, flg. 56. 



1863. Discina pelopea BILLINGS. Geology of Canada, p. 159, flg. 124. 



1892. Discina concordensis SARDESON. Bulletin of the Minnesota Academy of Natural Science, 



vol. iii, p. 328, pi. iv, flgs. 13, 14. 



Original description: "Upper valve circular, depressed-conical. Apex about 

 half the semi-diameter from the posterior margin. Surface with fine concentric 

 striae when perfect, but when partially exfoliated, smooth and places shining. Color 

 black; width, six lines. Lower valve unknown. 



The following emended description is prepared from a series of specimens 

 obtained from the quarries at Mantorville, Minnesota, in the Galena limestone 

 horizon: Shell circular, biconvex, with the apex of the dorsal valve situated at about 

 one-third the entire length of the shell from the posterior margin; apex of the 

 ventral valve somewhat more excentric. Surface with numerous concentric, 

 strongly elevated lines of growth, with the intermediate spaces wide and concave; 



