IDl) 



XX!. On a New Species of Grammysia from the 

 Chemung Group 



BY WILLIAM II. riTT. 



[liead before tJds Society, Decemher 2^ 1873.] 



Genus Cxraniniysia, DeVeriwuil, 

 Bulletin de la Soc. Geo!, de France, Vol. 4, p. 69G, 1847. 



M. De Verxeuil's generic description has been lately modifif d 

 by Professor James Hall, so as to inclnde the species which naturally 

 belong to the same group, as follows : 



Generic Characters. — Shell equivalve, inequilateral, varying from sub- 

 quadrate to transversely elliptical. Valves ventricose, sometimes inflated : 

 beaks strong, prominent and incurved ; binge line shorter than the shell, pos- 

 terior to the beaks. Dentition obscure, or represented onl_y by irregular folds 

 on the cardinal line : ligament external, prominent, extending from beneath 

 the beaks to nearly one-half the length of the hinge line. Cardinal margin 

 bordered by a deep, well-marked escutcheon; anterior end marked by a small, 

 deep an<l strongly defined lunule. Anterior and posterior muscular impres- 

 sions faintly marked, the latter much the larger: palleal line not sinuate, but 

 broken into points or ridges, strongly rounded posteriorly, and uniting with 

 the large muscular scar near its anterior border. 



Surface of shell often marked by an oblique mesial rib or fold, extending 

 from the beak to the basal border, and by numerous strong concentric folds 

 or ridges, which are frequently obsolete on the posterior part of the shell. 

 The shells appear to have been thin and fragile, and are usually much crushed 

 and distorted from compression ; but most of the species occurring in the New 

 York rocks are well marked, and not readily mistaken, since their specific 

 characters are easily distinguished. 



Notice of Lamellihranchiate Shells, Part 2, p. 48 [preparatori/ for the Paleon- 

 tology of New Tork^. 



Grammysia Chemungensis (n. s.), Plate 6. 



Shell attaining medium size, and, transversely, decidedly elliptical ; valves 

 ventricose; beaks strong, -incurved, and somewhat flattened; hinge line (as 

 near as can be determined from the specimen, which is a cast, left valve) less 



