120 SYNOPSIS OF THE CHARACTERS OF THE 



Lept^na multidentata. M'Coy. (PI. XX. fig. 8). 



Sp. Ch. — Semicircular; dorsal valve convex; ventral valve slightly concave ; hinge-line straight, furnished 

 with about twenty-six short, toothed spines ; cardial area triangular, narrow, smooth ; both valves coarsely striated 

 longitudinally ; strise often dichotomizing ; the intervening sulci regularly punctured. 



This fine species is distinguished from every iejotena I know, by the gi-eat number of short, strong spines 

 on the hinge-line ; the dorsal valve is convex towards the beak, flattened towards the cardinal angles ; the lon- 

 gitudinal strise are coarse, rounded, and frequently branching as they approach the margin ; they are separated 

 by very narrow sulci regularly punctured. Length eleven lines, width one inch five lines ; height of cardinal 

 area one line. 



LePT^NA PAPYEACEA. M'Coi). (PI. XXII. fig. 2). 



Sp. Ch. — Truncato-orbicular, length two-thirds the width, flat; hinge-line less than the width of the shell, 

 spinous ; cardinal angles obtuse ; surface radiated with sharp, filiform, unequally-branched strise, divergingly 

 arched at the sides ; sides of the shell concentrically wrinkled. 



This singular species is common in one or two localities. It is distinguished from all others of the genua 

 by the corrugated sides ; it is perfectly flat, and as thin as paper ; the hinge-line is considerably less than the 

 width of the shell, and is closely set with long, hooked, slender spines. Length ten lines, width eleven 

 lines. 



Lept^na perlata. M'Coy. (PL XX. fig. 9)- 



Sp. Ch. — Semicircular; nearly twice as wide as long, convex; front margin nearly straight; surface 

 marked with very fine, longitudinal, slightly flexuous strias ; hinge-line with about eight long, slender spines, 

 set nearly at right angles. 



This species is very closely allied to the L. lata of the Silurian strata; but on comparison of specimens 

 the present shell is found to have the radiating stris very much finer than either the Silurian species, or the O. 

 Hardrensis of Phillips, and that they are slightly flexuous, nor is there any mesial depression in the present 

 shell. Length three lines, width five and a half lines. 



Lept^na plicata. Phil. sp. 



Orthis pHcata. Phil. Pal. Fos Orthis plicata. Sow. Geol. Trans. 



Sp. Ch. — Transversely elliptical; width more than twice the length, extremities rounded, depressed; sur- 

 face with about thirty coarse, sharp, radiating ridges, which become doubled in number as they approach the 

 margin. 



This species seems closely allied to that which I have figured under the name o^Leptana serrata, but is dis- 

 tinguished by its angular plaits, and rounded extremities ; the radiating ridges are striated transversely. Length 

 three lines, width seven lines. 



LePT^NA SEEICEA. SoiV. (?) 

 LeptKna sericea. Sow. Sil. Syst. ? — Leptisna interstrialis. Pkil. Pal. Fos. 



Sp. Ch. — Semicircular, gibbous; very finely striated every fifth or sixth line, forming a sharp sulcus. 



The few specimens of this shell which have occurred to me are obviously identical with the Leptcena 

 ?'w<er«<r/a?/s of Phillips. That author states, that on comparison with specimens oi Xhe L. sericea, his shell 

 seemed distinct. I do not, however, see any very clear distinction in the Irish specimens, and they are referred 

 to that species for the present, until more perfect specimens may occur. Length about seven lines. 



