500 S. WELLER MISSISSIPPIAN RHYNCHONELLIFORM SHELLS 



creasing width to near the middle of the shell, and is even extended some- 

 what beyond the anterior limit of the median septum upon the floor of 

 the valve. 



In the pedicle valve the hinge-teeth are supported by strong dental 

 lamellae which are joined to form a broad spondylium supported by a 

 median septum from the floor of the valve. Beyond the articulation of 

 the valves the inner margins of the lamellse become free. The spon- 

 dylium is much broader and deeper than the cruralium of the opposite 

 valve and is attached to the floor of the valve by a much lower median 

 septum; it rapidly becomes shallower and narrower anteriorly, termi- 

 nating before the cruralium of the brachial valve has reached its maxi- 

 mum expansion. The median septum continues a short distance beyond 

 the extremity of the spondylium, but quickl}^ disappears. Hall and 

 Clarke^ mention "two accessory supporting lamellae abutting on one side 

 against the outer surface of the converging dental plates, and on the other 

 against the interior cardinal surface of the valve,'^ but these have not 

 been observed in any of the specimens sectioned, although they are pres- 

 ent in at least two of the species referred to the genus Camarophoria by 

 the same authors, C. subcuneata and C. suhtrigona, neither of which 

 species possess the true cruralium of the brachial valve which is so con- 

 spicuously developed in C. schlotheimi. 



CAMAROPHORIA HAMBUROEN8IS N. 8P. 



Among the Mississippian species which have been investigated, only 

 two possess the essential characters of Camarophoria as exhibited by the 

 genotype, and neither of these were referred to the genus by Hall and 

 Clarke. The first is an undescribed species which may be designated as 

 C. hamhurgensis. It occurs commonly in the thin Hamburg oolite bed 

 near the base of the Kinderhook at Hamburg, Calhoun County, Illinois.^ 

 The species occurs for the most part as detached valves, and a series of 

 sections of both the pedicle and brachial valves is shown in figure 2. In 

 the brachial valve this species is essentially like C. schlotheimi except 

 that the lateral processes of the median septum, which are produced into 

 the cruralium, arise nearer the floor of the valve, and their distal margins 

 do not curve up sufficiently to become attached to the under surface of the 

 hinge-plate, but always remain free (figures 2/?, I). As in C. schlotheimi 

 the median septum appears to pass through the cruralium in the apical 

 portion of the valve as a support to the hinge-plate, and after it has 

 ceased to render this support it is continued as a gradually disappearing 



^ Paleontology of New York, vol. vili, part 2, p. 213. 



« Transactions of the Academy of Science of Saint Louis, vol. xvl, p. 465. 



