TETRACAMERA 503 



ent order, as has been done by some students of the brachiopods. The 

 presence or absence of the pedicle median septum in the true Ehyncho- 

 nelloids is dependent solely upon the modification of certain elements, 

 the dental lamellae, which are present in all of the shells. The cruralium 

 of the brachial valve, on the other hand, as developed in the species of 

 Camarophoria, is a totally distinct morphologic element in the structure 

 of the shell, and its presence is well worthy of recognition as of more 

 than generic importance. 



Tetracameka n. gen.® 

 tetracamera subcuneata (hall) 



Among the rhynchonelliform shells possessing a pedicle median sep- 

 tum, and referred for the first time to the genus Camarophoria by Hall 

 and Clarke, is Rhynclionella subcuneata Hall. A series of cross-sections 



o O O o o o 



" 0)' ¥ w ¥. ¥/ 



7 



Figure 4. — Cross-sections of the 7'ostral Portion of Tetravamera siihcuneata (Hall) 



This series of ten cross-sect ious (x -Mj) is from a specimen from the Salem limestone of 



Indiana 



of this common species of the Salem limestone is shown in figure 4. 

 The median septum of the brachial valve is undivided at the apex of the 

 valve (figures 46, c. d), but before the articulation of the shell is reached 

 a median incision is formed internally which is at first arched over (figure 

 4e), but soon becomes open on the cardinal side by the incision between 

 the lateral divisions of the hinge-plate (figure 4/). This cruralium- 

 like or crural cavity^ is very short, not even extending anteriorly to the 

 articulation of the valves, although the median septum continues with 

 gradually decreasing height, sometimes to near the middle of the valve. 



8 Superfamily Rliynchonellacea Schuchert. 



8 Tills cavity Is morphologically different from the cruralium of Camarophoria, and 

 will hereafter be referred to as the crural cavity. 



