LAMELLIBRANCHIATA. 359 



plications. In its general form it also somewhat resembles G. Canadensis of 

 Billings, but is otherwise very distinct. 



Formation and locality. In the Corniferous limestone, Delaware, 0. 



Gkammysia bisulcata. 



PLATE LIV, FIGS. 1-16; PLATE LVI, FIG. 1 ; and PLATE XCIII, FIG. 25. 



Pholadomya anmnala, Goldpuss. Pet. Germ., p. 272, pi. 157, fi^. 9. 1834-1840. 



Ptennea bisulcata, Cokrad. Geol. Surv. N. Y., Ann. Rep., p. 116. 1838. 



Cypricardites bisulcata, Conrad. Geol. Surv. N. Y., Ann. Rep., p. 52. 1841. 



Qrammysia Hamiltoiumgis, Db Vkrneuil. Bull. Soc. Geol., France, 2d ser., vol. iv, p. 096. 1847. 



Cardinia Hamillonensis, D'Orbigny. Prod. Paleon., vol. 1, p. 76. 1850. 



Qrammysia bisulcata (Cokrad), Hall. Prelim. Notice Lamellibranchiata, 2, p. 49. 1870. 



PS'l- N. Y., vol. V, pt. 1. Plates and Explanations : PI. 54, figs 1- 

 16 ; pi. 56, fig. 1. 1883. 

 Compare Nucida cingulata, Hisikger. Leth. Svecica, pi. 39, fig-. 1 ; supplement, p. 6. 1837. 



Shell large, ovoid ; length once and a half the height ; basal margin broadly 

 curved, with a constriction near the middle of its length ; posterior margin 

 abruptly rounded below and broadly curving or sub-truncate above. Cardi- 

 nal line nearly straight, more than half as long as the shell. Anterior end 

 abruptly rounded below the deep lunule. 



Valves regularly convex below and gibbous or ventricose in the middle 

 and above. 



Beaks sub-anterior, strong, incurved over the cardinal line. Umbo promi- 

 nent, gibbous, with a cincture consisting of a strong fold with a furrow on 

 each side, extending from the beak to the basal margin at about the middle 

 of its length ; this feature, alternating on the two sides, gives a sinuosity to 

 the line of junction of the valves. 



Entire surface marked by fine concentric striae, which, on some portions ol 

 the shell, are aggregated into fascicles ; and by strong, regular, persistent, 

 concentric ridges or folds, which are stronger upon the anterior part of the 

 shell and distinctly undulated in crossing the cincture. The undulations occa- 

 sionally become obsolete in the lower and posterior part of the shell, and 

 sometimes are to be seen only on the anterior and umbonal portion. In well- 

 preserved specimens the surface, especially in the umbonal region, is also 



