LAMELLIBRANCHIATA. 363 



many individuals, it may be suggested that these are only old shells in which 

 the conspicuous markings have become obsolete. An approach to this condi- 

 tion is seen in fig. 8 of plate Ivii, which is referred to G. nodocostata. 



Formations and localities. In the arenaceous shales of the Hamilton group, in 

 Schoharie, Otsego, Chenango, Madison and Onondaga counties, and in the Che- 

 mung group at Ithaca, N. Y. 



Grammtsia erecta. 



PLATE LVI, FIG. 8 ; AND PLATE LVII, FIG. 10. 



Qrammyxia erecta. Hall. Pi-elim. Notice Lamellibranchiata, 2, p. 52. 1870. 



" magna. Hall, in error. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PI. 56, fig. 8 ; pi. 



57, tig-. 10. 1883. 



Shell of medium or large size, erect, sub-triangular ; length one-fourth greater 

 than the height ; basal margin gently rounded except where slightly sinuated 

 by the cincture near the middle of its length ; posterior margin abruptly 

 rounded below and recurving to the cardinal line, which is short. Anterior 

 end below the lunule, broadly rounded. 



Valves regularly convex below and gibbous above. 



Beaks sub-anterior, very prominent and strongly incurved. Umbo ven- 

 tricose ; umbonal slope rounded and arcuate. Cincture in the right valve, 

 consisting of a fold and shallow furrow on each side, beginning at the beak, 

 and extending in a curving direction to near the middle of the base. 



Surface marked by fine concentric striae, which become fasciculate on the 

 anterior half of the shell, and form strong angular elevations. These con- 

 centric undulations extend over the entire umbonal region, and are abruptly 

 sinuate in passing the cincture. Surface also marked by extremely fine 

 riuliating striae. 



This species differs from any of those having a cincture, in its erect form and 

 sub-triangular outline. The specimens are distorted and fragmentary, and 

 therefore unsatisfactory. 



Formation and locality. In the shales of the Hamilton group, at Fultonham, 

 Schoharie county, N. Y. 



