BLACK RIVER BRACHIOPODS 
71 
tinues to the anterior margin as a broad, shallow depression oc- 
cupied by four to eight strong, angular plications. 
Brachial valve more convex than the pedicle, depressed in the 
umbonal region and abruptly downcurved in the anterior. Mesial 
fold originates 5 to 6 mm. anterior to the beak ; it is. a broad, low 
elevation bearing one more plication than does the sinus. Surface 
of both valves marked by fifteen to twenty-five simple, subangular 
plications, with no growth lines in the specimens examined. 
This species was described by Sardeson from the upper Platte- 
ville (“Trenton”) of Minnesota; Winchell and Schuchert fail 
to distinguish it from “ Rhynchotrema inequivalvis” and probably 
refer to it forms that do not properly belong there. The collec- 
tions in Walker Museum contain sets from the Platteville at Min- 
neapolis and at Ellsworth, Wisconsin, the latter having been iden- 
tified by Mr. Sardeson, and a single pedicle valve from the De- 
corah Shale at Ste. Genevieve, Missouri. The Ellsworth speci- 
mens, from which are selected the plesiotypes, are narrower, with 
fewer and coarser plications than the two Minneapolis specimens 
and the one from Ste. Genevieve. From R. wisconsinense of this 
paper they may be distinguished by their greater size, more nu- 
merous plications, and lack of lamellose growth lines. 
Plesiotypes, No. 27,443, Walker Museum. 
RHYNCHOTREMA WISCONSINENSE sp. nov. 
Plate I, figs. 6-8. 
Shell small, subovate, wider than long, with the postero-lateral 
• margins curved and slopes without vertical flattening. Dimen- 
sions of two specimens, the first of which is the holotype : Length, 
11 mm., and 9.6 mm.; width, 12.7 mm., and 11.6 mm.; thickness, 
8.6 mm., and 7.8 mm. ; width of sinus, 5.8 mm., and 5.8 mm. 
Pedicle valve moderately convex, with the slopes flattened. 
Beak sharp, prominent, slightly incurved, with the delthyrium 
partly occupied by the brachial beak. Mesial sinus originates 3 
to 4 mm. from the beak, extending as a broad, flat-bottomed 
trough to the margin; it is marked by three (rarely four) strong, 
angular plications. 
Brachial valve more convex than the pedicle ; umbo slightly de- 
pressed ; beak abruptly incurved. Slopes curve abruptly to the 
anterior margin; less so to the postero-lateral. Mesial fold high, 
flattened, sharply defined, its plications numbering one more than 
. those of the sinus. Surface of both valves marked by twenty 
