BLACK RIVER BRACHIOPODS 
73 
sions of three specimens, the third of which is the holotype : 
Length, 8 mm., 8.3 mm., and 9 mm. ; width, 9.8 mm., 8.8 mm., 
and 11.2 mm.; thickness, 5.1 mm., 4.8 mm., and 5.4 mm.; width 
of sinus, 5.2 mm., 4.9 mm., and 5.6 mm. 
Pedicle valve convex in the umbo but flattened on the slopes; 
beak sharp, incurved, and produced beyond that of the opposite 
valve. Mesial sinus broad, sharply defined, with three strong, 
simple, angular plications. Brachial valve more convex than the 
pedicle, due to its shortness, but as shallow as, or shallower than, 
the pedicle. Umbo slightly flattened ; beak sunk into the delthyri- 
um. Mesial fold broad, sharply defined but flattened, and bear- 
ing in all specimens examined four strong, simple, angular pli- 
cations. Surface of both valves marked by fifteen to twenty 
plications, the average being sixteen or seventeen. Growth lines 
present in but one specimen, that a deformed one. 
While this species seems to be characteristic of the Decorah 
shale in Iowa, it has not been collected in Ste. Genevieve county. 
Surprisingly enough, however, it occurs in its typical form in the 
lower portions of the Maquoketa stage in the neighborhood of 
Clermont, Iowa, sets being in the collections of both Walker Muse- 
um and the University of Iowa. 
Holotype, No. 25,632; Paratypes, No. 25,611, Walker Museum. 
RHYNCHOTRBMA MISSO URIBNSB sp. nov. 
U 
Plate I, figs. 22-26. 
Shell small, subovate to subtriangular, as wide as or wider than 
long; postero-lateral slopes with slight vertical flattening. Di- 
mensions of three specimens, the second and third of which are 
the cotypes: Length, 11.5 mm., 10 mm., and 9.3 mm.; width, 13.3 
mm., 10.2 mm., and 9.7 mm. ; thickness, 9.5 mm., 8.3 mm., and 6 
mm.; width of sinus, 5.7 mm., 5.8 mm., and 5.1 mm. 
Pedicle valve convex on the umbo ; flattened on the lateral slopes, 
and abruptly convex to the margins. Beak acutely angular, in- 
curved, and produced 1 to 1.6 mm. beyond that of the opposite 
valve. Mesial sinus broad, shallow, flat-bottomed, containing, 
in all specimens examined, three plications ; it originates 4 to 5 
mm. anterior to the beak, and curves with increasing abruptness 
toward the opposite valve. 
Brachial valve more convex than the pedicle; beak short and 
sharply incurved into the delthyrium ; region anterior to the umbo 
slightly flattened; antero-lateral slopes abruptly convex. Mesial fold 
