BRACHIOPODA. 365 
Schizotretii] 
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 Iliver (Hudson River) group or Loraine shales near 
Spring Valley, Minnesota. Also in thie Trenton formation at Middlcville and Lowville, New York; 
Bellville and Ottawa, Canada. 
Collector. — Charles Schuchert. 
Genus SCHIZOTRETA, Kutorga. 
1848. Schizotreta, Kutokga. Verhandl. der russ.— Kais. Mineral. Gesellsch. zu St. Petersburg, 
pp. 272, 273. 
1890. Schizotreta, Hall. Palaiontology of Now York, vol. viii, abstract, p. 13.5. 
This subgenus is readily distinguished from Orbiculoidea " in having the perfor- 
ated valve very convex and the imperforate one depressed-conical or flat. 
" The pedicle-groove has essentially the character seen in Orhiculodea, 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. 
Schizotreta pelopea Billings, sp. 
l^LATE XXIX, FIGS. 26-28. 
1862. Discina pelopea Billings. Palaeozoic Fossils, vol. i, p. 52, flg. 56. 
1863. Discina pelopea Billings. Geology of Canada, p. 159, fig. 124. 
1892. Discina concordensis Sardeson. Bulletin of the Minnesota Academy of Natural Science, 
vol. iii, p. 328, pi. iv, figs. 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; 
