Lamellibranchiata. 289 



Pterinea dispanda. 



Pterinea dispanda, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: 

 PL 15, fig. 7. Jan., 1883. 



Shell large; body very broadly ovate, nearly erect; length greater 

 than the height ; anterior margin very convex ; basal margin flat- 

 tened, nob produced posteriorly. Left valve regularly convex, and 

 only moderately gibbous on the umbo. Right valve unknown. 

 Hinge-line straight, greater than the length of the body, extended 

 posteriorly beyond the margin of the valve. Beak anterior, nearly 

 rectangular, prominent, directed forward. Umbonal region ample. 

 Ear small, separated from the body of the shell by a broad unde- 

 fined sulcus, which is marked by several oblique folds. Byssal sinus 

 deep and abrupt. Wing very large, depressed-convex, broad-tri- 

 angular ; defined by the retral curving of the concentric striae; con- 

 cave on the margin ; extremity extremely produced and acute. 



Test ornamented with strong, unequal, rounded radii, which are 

 sometimes bifurcating on the anterior portion. The wing is marked 

 with similar smaller rays which are sometimes fasciculate. Entire 

 surface also marked by concentric lamellose strias, which at irregu- 

 lar intervals are crowded into fascicles, giving an undulating aspect 

 to the surface, and a low nodose appearance to the stronger rays. 



The specimen described has a height of 70 mm., lengch about 80 

 mm., and the length of the hinge-line about 90 mm. 



This shell bears some resemblance to the more extravagant forms of 

 Pterinea flabella, but it is larger than any known specimen of that 

 species, with a proportionally longer and less defined body, and dis- 

 tinctly different surface ornamentation. 



Formation and locality. In the upper beds of the Chemung group 

 at Mansfield, Tioga county, Pa. 



Pterinea Chemungensis. 



Avicula Chemung 'ensis, Conrad. Jour. Acad. Nat. Sci., Phila., vol. 8, p. 243. 



1842. 

 Avicula pecteniformis, Hall. Geolog. Surv. N. Y.: Rept. Fourth Dist., p. 262. 



1843. 

 Pterinea Chemungensis (Conrad), Hall. Pal. N. Y., vol. v, pt. 1. Plates and 



Explanations : PI. 16, figs. 3, 7, 10, 12. Jan., 1883. 



Shell very large, rhomboidal ; body of shell ovate, narrower above, 



nearly erect, or sometimes oblique ; length less than the height ; 



greatest length below the middle ; basal and post-basal margins 



rounded ; the anterior margin above the middle is nearly straight, 



[Sen. Doc. No. 38.] 37 



