434 MISSISSIPPIAN BRACHIOPODA 



valve 33 mm., length of brachial valve 27.5 mm., maximum width 37 mm., 

 length of hinge-line 22 mm., thickness 22.5 mm., height of cardinal area 

 4.5 mm. 



Pedicle valve rather strongly convex, the greatest convexity posterior 

 to the middle, the surface curving abruptly from the umbonal region to 

 the cardinal margin, less abruptly to the lateral and still more gently to 

 the anterior margin; mesial sinus shallow, rather broad, ill-defined, orig- 

 inating in the umbonal region; beak apparently of moderate size, in- 

 curved; cardinal area of moderate height, concave, the lateral margins 

 not defined, the surface curving into the lateral slopes of the valve with 

 no line of differentiation ; the delthyrium open, broadly triangular. Inter- 

 nally the hinge-teeth are supported by a pair of rather strong dental 

 lamella? of unknown anterior extension, between which is a median septum 

 whose anterior extension is also unknown; character of the muscular 

 scars and the internal configuration of the valve unknown. 



Brachial valve less convex than the pedicle, the greatest convexity pos- 

 terior to the middle, the umbo projecting somewhat beyond the cardinal 

 line, the surface curving abruptly to the cardinal margin and much more 

 gently to the lateral and anterior margins, somewhat compressed towards 

 the cardinal extremities ; mesial fold almost obsolete, only slightly distin- 

 guishable towards the front of the valve, where it is only slightly differ- 

 entiated from the general convexity; beak short and incurved; cardinal 

 area inconspicuous. The internal characters of the valve not observed. 



Surface of both valves marked by regular concentric bands from 2 to 3 

 mm. in width along the median line of the shell, the surface of each suc- 

 cessive band being slightly but abruptly depressed below the one imme- 

 diately preceding it; the concentric bands are marked by low, elongate 

 nodes about 1 mm. apart, which are arranged in more or less regular radi- 

 ating lines from the beak to the lateral and front margins and which are 

 more prominent towards the anterior margin of the concentric bands. 

 Upon some portions of the shell the anterior extremities of the nodes are 

 distinctly bilobed, showing that they were produced in double-tubed 

 spines. 



Remarks.- The type specimen of this species is a nearly complete ex- 

 ample with the beak of the pedicle valve slightly restored. The shell 

 surface is exfoliated so that the surface spines have nowhere been pre- 

 served, but the character of the nodes which represent the spine bases 

 are such as to indicate that the characteristic double-tubed spines of the 

 genus were present. The species differs from R. setigera, which occurs in 

 the same fauna, in the slightly developed or nearly obsolete fold and sinus 

 and in the much coarser surface spines. From R, pseudclineata of the lower 

 beds it differs in the much coarser spines, somewhat greater proportional 

 length, and apparently in the absence of the distinct internal radiating 

 costae. The internal characters of the shell are not clearly exhibited in 



