474 MISSISSIPPI AN BRACKIOPODA 



prouti, so the name cannot be used to designate the shell under considera- 

 tion. C. glenparkensis is perhaps most closely related to C. hirsuta, 

 but it is larger than that species and is proportionally broader and 

 thinner, with more crowded and thinner pectinated lamella 3 . It differs 

 from C. sublamellosa, which has sometimes been referred to C. roissyi 

 in being broader and thinner, and in having the valves subequally 

 convex. In size the species exhibits considerable variation, some examples 

 attaining a length of 30 mm. or more, but none of these larger individuals 

 have been observed in an undistorted condition. 

 Horizon. Fern Glen formation. 



CLIOTHYRIDINA PROUTI (Swallow) 

 Plate LXXIX, Figs. 13-16 



1860. Spirigera Proutii Swallow, Trans. St. Louis Acad. Sci., vol. 1, p. 649, 

 1881. Spirifera temeraria Miller, Jour. Cinn. Soc. Nat. Hist., vol. 4, p. 314, 



pi. 7, figs. 9-9b. 



1894. Athyris proutii Keyes, Mo. Geol. Surv., vol. 5, p. 91. 

 1909. Cleiothyris prouti "teller, Bull. Geol. Soc. Am., vol. 20, p. 314, 



pi. 14, figs. 12-15. 



Description. Shell transversely subelliptical in outline, the greatest 

 width near the mid-length of the shell, the hinge-line shorter than the 

 greatest width, the cardinal extremities rounded, the fold and sinus con- 

 spicuously developed. The dimensions of two individuals are: length 

 17.5 mm. and 16 mm., width 22.5 mm. and 21.5 mm., thickness 15 mm. 

 and 11 mm. 



Pedicle valve strongly convex, most prominent posterior to the middle, 

 the surface curving strongly from the umbonal region to the margins, 

 most abruptly to the cardinal margin ; mesial sinus large and deep, 

 originating near the beak and becoming proportionally more profound 

 anteriorly, rounded in the bottom, defined on each side by a rounded 

 ridge, in mature individuals produced anteriorly into a lingual extension 

 of greater or less length ; beak rather prominent, incurved, in close contact 

 with the umbo of the opposite valve, pierced by a circular foramen; 

 cardinal area obsolete except in old shells in which there is a more or 

 less conspicuous, flattened border or false cardinal area along the car- 

 dinal margin; delthyrium broadly triangular, nearly filled by the beak of 

 the opposite valve. 



Brachial valve strongly convex, the greatest convexity near or anterior 

 to the middle, the surface rather strongly convex from the cardinal to 

 the anterior margin ; mesial fold obscure or obsolete posteriorly, becoming 

 strongly developed anteriorly, especially in old shells, more or less ill- 

 defined laterally ; the beak strongly incurved, nearly filling the delthyrium 

 of the opposite valve. 



