80 SYNOPSIS OF THE CHARACTERS OF THE 



gin, which, being interrupted by the scaly laminse of growth, form minute, adpressed spines at the intersec- 

 tions. 



This is one of the thinnest and most delicate of our fossil square Avicula, the concentric lamina of growth 

 are rather irreo-ular, shewing the fragile nature of the shell at all ages ; the narrow threadlike strias being 

 frequently interrupted by the lamince of growth, give an echinated character to the surface, there is a flat 

 space behind the hinge, about one line in breadth. Length one inch one line, width one inch one and a half 

 lines. 



MeLEAGRINA LiEVIGATA. M'Coj/. (PI. XII. fig. 5). 



Sp, CA.— Orbicular, oblique, convex, smooth ; posterior ear undefined, rectangular ; anterior ear very 

 small, deeply divided from the body of the shell. 



The smoothness of the surface will at once distinguish this species oi Margarita from all its congeners; 

 the surface is slightly but uniformly convex ; the hinge-line is half the width of the shell, its extremities rect- 

 ano-ular ; anterior car half the length of tha posterior ; the anterior side is dilated, so as to give a slight obliquity 

 to the outline. Length one inch six lines, width one inch nine lines. 



Meleageina pulchella. M'Coy. (PL XII. fig. 6). 



Sp. Ch Longitudinally ovate ; hinge short, slightly oblique ; ears obtuse ; radiating ridges in pairs, plain 



on the sides, decussated by concentric undulations, and nodulous in the middle. 



This pretty little shell may be known from the other mountain limestone species by its large ribs running 

 in pairs from the beak to the margin ; they are nodulous only on the convex middle part of the shell, where 

 also they are crossed by obtuse concentric furrows, becoming obsolete on the sides ; the number of longitudinal 

 radii about twenty. Length five lines, width five lines. 



This is a scarce fossil. The specimen figured is the only one I have seen. 



Meleageina quadeata. M'Coy. (PI. X. fig. 5). 



Sp. C7;.— Subquadrate, slightly oblique; hinge-line straight; posterior ear twice the length of the anterior 

 ear, scarcely defined from the body of the shell ; surface smooth, with obscure, concentric wrinkles. 



This species may be distinguished from tlie others of the genus by its quadrate form, rectangular ears, and 

 smooth, obsoletely wrinkled surface. Length five lines, width five lines. 



Meleageina kadiata. Fhil. sp. 



Avicula radiata. Phil. Geol. York. 



5^;. C/i.— Semicircular, hinge-line straight, ears acute; posterior ear undefined, twice the length of the an- 

 terior ear ; surface with about twenty-five narrow, radiating ribs. 



This species diffbrs from the M. tessvllata, chiefly in its smaller size, and the greater number of the radiat- 

 ing ridt^e, the posterior ear is also somewhat larger. Length four lines, width five lines. 



Meleageina eigida. MCoy. (PI. XIII. fig. 16). 



Sp. Ch. Longitudinally obovate, convex; anterior ear large, square; posterior ear about a third longer 



than the anterior, pointed ; surface with about sixty-five rather distant, narrow, rough, radiating ridges, crossed 

 by a few large, irregular, concentric wrinkles. 



This fine shell runs no risk of being confounded with any others of its genus. The specimens obtained 

 were of a brilliant, silvery white. The radiating ribs are narrow, rough, and separated by broad flat spaces. 

 Length one inch nine lines, width one inch ten lines. 



