826 Report oF THE STATE GEOLOGIST. 
substance of the valve. Deltarium very conspicuous, convex, 
the component plates, in their later development, being anchy- 
losed along the median suture. Dental lamellz vertical, resting 
on the bottom of the valve and inclosing a deeply impressed 
muscular scar; diductor scars elongate-flabelliform, divided by 
oblique ridges into anterior and posterior members; adductor 
impression central, elongate and very small. The brachial 
valve bears a median septum which extends for one-half the 
length of the shell, is divided toward its posterior extremity, 
each branch supporting one process of the divided hinge-plate. 
The crura are long, slightly curved and somewhat expanded at 
their tips; between these there is a small, simple, cardinal 
process. 
External surface covered with exceedingly fine, rounded, fili. 
form, concentric lines. Shell-substance fibrous, impunctate. 
Type, Rhynchotreta cuneata, Dalman (sp.). 
Distribution. Lower — Upper Silurian. 
Stenoschisma, Conrad. 1839. 
(Plate 42, figs. 22-24.) 
Subtrihedral, coarsely plicate shells ; teeth supported by parallel 
vertical lamellz ; median septum of the brachial valve obscure or 
absent; median subcardinal cavity such as is found in Camaro- 
TaCHIA, wanting, the hinge-plate being divided by a median 
fissure which extends to the bottom of the shell and contains a 
slender longitudinal cardinal process; crura long, recurved and 
expanded at their extremities; surfaces of the dental sockets not 
crenulated. 
Type, Stenoschisma formosa, Hall (sp.). 
Distribution. Lower Helderberg. 
Camaroteechia, Hall. 1892. 
(Plate 43, figs. 1-9.) 
Shells somewhat variable in exterior though usually main- 
taining a full trihedral contour with shallow pedicle-, and convex 
brachial valves, evincing little, if any, evidence of a reversal at 
maturity of the relative convexity of early growth, a feature 
apparent in some of the other groups of the rhynchonelloids. 
The median septum of the brachial valve is divided posteriorly 
78 
