218 MISSISSIPPIAN BRACHIOPODA 



Remarks. The specimens here described occur commonly in the cherts 

 of Callaway County, Missouri, the locality and horizon of the type of the 

 species described by Swallow as Rhyncho-nella ringens, and they conform 

 in general outline with the shell suggested by the original definition of 

 that species. However, 110 examples have been observed by the writer to 

 attain more than about one-half the size of Swallow's type and none of 

 the specimens exhibit a distinct mesial sinus, which, in the original defini- 

 tion of the species, is said to be broad and shallow 7 ; furthermore, the plica- 

 tions are more numerous. If the shell here defined should ev.er attain so 

 large a size as is indicated by Swallow, it is not improbable that a shallow 

 mesial sinus might be developed, but the number of plications ought 

 to be somewhat greater in the larger example rather than smaller. How- 

 ever, if this shell does not belong to Swallow 's species, and it is believed 

 that it does not, it must be an undescribed form. 



The species most closely resembles T. arctirostrata, but it is a larger 

 and more elongate shell, and in the specimens observed, lacks a mesial 

 depression in the anterior portion of the pedicle valve. The species may 

 further be differentiated by reason of the occasional intercalation of 

 plications, in some specimens, which has not been observed in 

 T. arctirostrata. 



Locality. Callaway County, Missouri (residual chert). 



TETRACAMERA SUBTRIGONA (Meek and "Worthen) 

 Plate XXIX, Figs. 1-13 



1860. Rhynchonella subtrigona' Meek and "Worthen, Proc. Acad. Nat. Sci. 



Phil., p. 451. 

 1860. Rhynchonella Parvini McChesney, Desc. New Foss., pt. 2, p. 83. 



1865. Rhynchonella Parvini McChesney, Plates 111. New Spec. Foss., pi. 



6, figs. 2a-b. 



1866. Camarophoria subtrigona Meek and Worthen, Geol. Surv. 111., vol. 2, 



p. 251, pi. 18, figs. 7a-c. 

 1868. Camarophoria subtrigona McChesney, Trans. Chicago Acad. Sci., vol. 



1, p. 31, pi. 6, figs. 2a-b. 

 1894. Camarophoria subtrigona Hall and Clarke, Int. to Study of Brach., 



pt. 2, pi. 45, figs. 1-2. 



1894. Rhynchonella subtrigona Keyes, Mo. Geol. Surv., vol. 5, p. 102. 



1895. Camarophoria subtrigona Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, 



pi. 62, figs. 38-43. 

 1895. Camarophoria ringens Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, 



pi. 84, fig. 45. 

 1910. Camarophoria ringens Greger, Am. Jour. Sci. (4), vol. 29, p. 71, 



figs. 7-8. 

 1910. Tetracamera subtrigona Wfeller, Bull. Geol. Soc. Am., vol. 21, p. 



504, fig. 5. 



Description. Shell of medium size or larger, broadly subtriangular or 

 subpentagonal in outline, wider than long, truncated in front, with broad, 



