GIRTYELLA 273 



Remarks. The holotype of this species is a nearly complete internal 

 cast in which the dental lamellae of the pedicle valve and the median 

 septum of the brachial valve are clearly exhibited as slits. The species 

 is referred to the genus Girtyella because of the strong median septum of 

 the brachial valve, and, although the characters of the hinge-plate are not 

 clearly shown in the specimen, there can be no doubt as to the correct 

 generic reference of the species. The species is the largest member of the 

 genus here recognized, and seems to agree more closely with G. indianensis 

 than with any other, but the shell is proportionally broader and more 

 rotund in contour than that species. 



Horizon. Northview shale and upper Chouteau limestone of the Kin- 

 derhook. 



GIRTYELLA TURGIDA (Hall) 

 Plate XXXIV, Figs. 25-36 



1856. Terebratula turgida Hall, Trans. Albany Inst., vol. 4, p. 6. 



1882. Terebratula turgida Whitfield, Bull. Am. Mus. Nat. Hist., vol. 1, 



p. 54., pi 6, figs. 53-58. 



1883. Terebratula turgida Hall, 12th Ann. Rep. Geol. Surv. Ind., p. 336, 



pi. 29, figs. 53-58. 



1893. Dielasma turgida \Beecher and Schuchert, Proc. Biol. Soc. Wash., 



vol. 8, pp. 71-74, pi. 10, figs. 1-6. 



1894. Dielasma turgida Hall and Clarke, Int. to Study of Brach., pt, 2, 



pi. 53, fig. 11 (not figs. 10, 12). 



1895. Dielasma turgida Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, pi. 81, 



figs. 5-6 (not figs. 1-4, 7-8). 

 1906. Dielasma turgidum Beede, 30th Ann. Rep. Geol. Surv. Ind., p 1309, 



pi. 22, figs,' 53-58 (not pi. 19, figs. 5-5a). 

 1911. Girtyella turgida Weller, Jour. Geol., vol. 19, p. 443. 



Description. Shell small, subovate or subpentagonal in outline, the 

 anterior margin usually emarginate but sometimes straight, the greatest 

 width near or anterior to the middle, sometimes nearly at the front of 

 the shell, the valves more or less gibbous. The dimensions of two indi- 

 viduals, the larger one an exceedingly gibbous example, are: length of 

 pedicle valve 7.7 mm. and 8.3 mm., length of brachial valve 6.6 mm. 

 and 6.8 mm., greatest width 6.2 mm. and 6.1 mm., thickness 5.2 mm. 

 and 7.2 mm. 



Pedicle valve most convex posterior to the middle, the surface curving 

 abruptly from the umbonal region to the postero-lateral margins, be- 

 coming inflected towards the cardinal extremities, curving more gently 

 to the antero-lateral and anterior margins; mesial sinus originating in 

 or just in front of the umbonal region, of moderate width, its lateral 

 boundaries rounding into the lateral slopes, rounded in the bottom and 

 often becoming rather deep anteriorly ; the beak prominent, rather blunt, 



