BLACK RIVER BRACHIOPODS 
69 
three simple, angular plications, which are finer and more crowded 
than those of the slopes. Postero-lateral slopes with a slight ver- 
tical flattening and obscuring of the plications. 
Brachial valve more convex than the pedicle ; beak abruptly in- 
curved into the delthyrium; postero-lateral slopes flattened to cor- 
respond to those of the opposite valve. Mesial fold high and 
sharply defined, bearing four strong, crowded, angular plications. 
Total number of plications on each valve ranges from thirteen to 
sixteen, the commonest being fourteen. Anterior portions of both 
valves marked by numerous lamellose growth-lines. 
The variety seems to be an intermediate between R. kentucki- 
ense and R. mercerense of this paper. Its affinity to the former 
is shown in the rounded postero-lateral margin, the tendency to- 
ward subovate shape, particularly in the young, the high propor- 
tion of width to length in young (very near that of R. kentucki- 
ense), and in the lamellose growth-lines. The relationship to the 
latter is found in the postero-lateral flattening, the crowding of 
plications on fold and sinus, and in the great height and angularity 
of the plications. 
Formation and Localities : Kimmswick Limestone, near Batch- 
town, 111., and Sulphur Springs, Mo. 
Holotype, No. 27,451, Walker Museum. 
RHYNCHO T REM A MERCERENSE sp. nov. 
Plate II, figs. 17-21. 
Shell of less than medium size; in the young specimens, longer 
than wide and acutely subtriangular; in the adults, wider than 
long, gibbous, and broadly subtriangular. Postero-lateral mar- 
gins straight and vertically flattened in young specimens ; slightly 
curved and convex in adults. Dimensions of cotypes : Length, 
9.9 mm. and 12.9 mm.; width 8.7 mm. and 13.1 mm.; thickness 
6.2 mm. and 10.6 mm.; width of sinus 5.1 mm. and 8.3 mm. 
Pedicle valve moderately convex in the umbonal region ; lateral 
slopes flattened. Beak sharp, slightly incurved, and projected be- 
yond that of the brachial valve. Mesial sinus originates 4 to 5 
mm. anterior to the beak ; in the young it forms a narrow, shallow 
depression which curves gently to the anterior margin; in the 
adults the curve is more abrupt. In the adult cotype the depth 
of the sinus at the anterior margin is 4.6 mm. 
Brachial valve more convex than the pedicle, with the postero- 
