SOME BLACK RIVER BRACHIOPODS FROM THE 
MISSISSIPPI VALLEY 
CARROLL LANE FENTON AND MILDRED ADAMS FENTON 
This study originated in the attempt to identify a number of 
Rhynchotremas and Zygospiras from the Plattin and Decorah 
formations of Ste. Genevieve county, Mo. Comparisons were 
made with sets from several other localities in the Mississippi val- 
ley, and thus considerable additional material was examined, in- 
volving not only Black River horizons, but the Kimmswick and 
Maquoketa as well. The results of the study may be summarized 
in three conclusions: 
1. It has become customary to apply the terms Rhynchotrema 
inequivalve and Zygospira recurvirostris indiscriminately, 
to specimens from numerous horizons and localities. 
2. Rhynchotrema inequivalve was not recognizably described 
and illustrated by Castelnau, and later authors have used 
the name without redescribing the original types. 
3. Among the forms of the genera Rhynchotrema and Zygo- 
spira commonly referred to the two species here named 
there are several heretofore undescribed species and varie- 
ties. 
In the following pages are descriptions and illustrations of such 
of these forms as have come into the hands of the authors. 
RHYNCHOTREMA KENT U CKIENSE sp. nov. 
Plate I, figs. 4-5; 18-22 
Shell of medium or smaller than medium size, wider than 
long, and with postero-lateral margins curved and without notice- 
able flattening. Dimensions of three specimens, the first of which 
is the holotype : length, 12.6 mm., 12.8 mm., and 10.1 mm.; width, 
14.9 mm., 15.7 mm., and 10.5 mm.; thickness, 11.2 mm., 10.4 
mm., and 5.7 mm.; width of sinus, 7.7 mm;., 8.5 mm., and 5.1 mm. 
Pedicle valve convex in the umbonal region ; flattened on the 
lateral slopes. In young specimens the slopes reach the margins 
without an increase in convexity; in adults such as the holotype 
the convexity is very abrupt, being accomplished by numerous 
