206 



MISSISSIPPIAN BRACHIOPODA 



plate is undivided so that the crural cavity is closed internally, but ante- 

 riorly the hinge-plate is divided and the crural cavity is open as in 

 Camarotoechia, but the borders of the cavity are extended beyond the 

 hinge-plate and are somewhat convergent so that the opening into the 

 crural cavity is narrowed and slit-like. The crura are formed by the an- 

 terior extension of the inner margins of the two portions of the divided 



FIG. 15. A series of nine cross-sections of the rostral portion of the shell of 

 Rhynchotetra missourlensis (X 2y 2 ), showing the dental lamellae of the 

 pedicle valve joined to form a spondylium supported by a median septum; and 

 the median septum, crural cavity, and crura of the brachial valve. 



hinge-plate and the adjacent portions of the walls of the crural cavity, 

 and the median septum is extended conspicuously along the floor of the 

 valve beyond the anterior margin of the crural cavity. 



Remarks. The members of this genus have sometimes been included in 

 the pentameroid genus Camarophoria because of the presence of a distinct 

 median septum in each valve, with the spondylium in the pedicle valve, 

 but they lack entirely the cruralium in the brachial valve, which is so 

 characteristically developed in that genus, between the hinge-plate and 

 the floor of the valve. Some of the species have also been described as 

 members of the genus Paryphorhynchus because of the fine radiating striae 

 upon the surface of the shell, but the internal structure of the two genera 

 is entirely different. 



RHYNCHOTETRA CAPUT-TESTUDINIS (White) 

 Plate XXVII, Figs. 1-6 



1862. Rhynchonella caput-testudinis White, Proc. Boston Soc. Nat. Hist., 



vol. 9, p. 23. 



1894. RKymchonella sp. ? Keyes, Mo. Geol. Surv., vol'. 5, pi. 41, fig. 11. 

 1901. Camarophoria caput-testudinis Weller. Trans. St. Louis Acad. Sci., 



vol. 11, p. 196, pi. 19, figs. 1-4. 



