102 PALEONTOLOGY OF KENTUCKY. 



subangular ridge. It differs from all other species of the Niagara and Lower 

 Helderberg groups, but approaches in some characters to Meristella (Atrypa) 

 crassirostrata of the Niagara group. From Meristina nitida, with which it is 

 usually associated, it differs greatly, and is therefore easily distinguished. 



Formation and Locality. Found in the Niagara strata in the quarries east of the city of Louis- 

 ville, Ky., where it is, however, somewhat rare, at least in well preserved specimens, while at Waldron, 

 Indiana, it occurs in great abundance, and of great beauty and perfection. 



Meristina nitida. HALL. 



Plate XXXIII.. figures 10 and 11. 



Atrypa nitida, Hall. Geol. of N. Y., Geol. Sur. 4th dist., Tab. of Org. Remains, p. 111848. 

 Atrypa nitida, Hall. Pal. N. Y., Vol. II., p. 268, pi. 651852. 

 Merista nitida, Hall. 12th Eep. St. Cab. Nat. Hist., p. 781859. 

 Meristella nitida, Hall. Trans. Alb. Inst., Vol. IV., p. 2261863. 

 Meristina nitida. Hall. Pal. N. Y., Vol. IV., p. 2991867. 

 Meristina nitida, Hall. 28th Eep. N. Y. St. Mus., Nat. Hist. Edit., p 1601879. 

 Meristina nitida, Hall, llth Geol. Eep. of Indiana, p. 3001881. 



Shell, as found in the neighborhood of Louisville, of small size ; those found 

 at Waldron, Indiana, of medium size, sub-triangular, with a sinuate base and 

 largely extended beaks ; most of the shell only moderately convex, but some 

 becoming very gibbous, even, in isolated instances, per-gibbous ; lateral and 

 basal margins broad and square, owing to the fact that in both valves the mar- 

 ginal borders inflect almost rectangularly. Only in few individuals do both 

 valves slope regularly without inflection to their edges, and meet under an 

 acute angle (see figures 10 and 11, plate 33). Ventral valve usually of equal 

 convexity with dorsal, showing in its basal third a slight depression, which 

 terminates in basal inflection or emargination ; the beak is much elevated above 

 and incurving over beak of the opposite valve 



Dorsal valve has no indication of a mesial elevation ; its beak is strongly 

 incurved into ventral valve. There are no surface-markings except a few con- 

 centric lines of growth. 



Formation and Locality. It occurs usually associated with Meristina maria in the Niagara strata 

 east of the city of Louisville, Ky.; it is, however, not as rare as that species, but is found pretty abundantly 

 and also in very small but well preserved specimens. Shells of this species from Waldron, Indiana, are 

 often of more than double size of even our largest individuals. This species is easily identified, inasmuch 

 as it differs considerably from all other species of the Upper Silurian formation. The shells figured are 

 different from the usual forms. 



