CARBONIFEROUS FOSSILS OF IRELAND. 137 



like the C. senilis, Phil., the mesial fold is obsolete ; the dorsal and ventral valves are evenly convex ; cardinal 

 angles acute in the young, rounded in tlic old shells ; the stria: are coarse, round, and equal. Length two 

 inches four lines, widtli two inches ten lines ; height of cardinal area one inch three lines. 



Ctrtia laminosa. M'Cot/. (PI. XXI. fig. 4). 



Sp. Ch. — Semicircular, about twice as wide as long; cardinal area wide, triangular; surface with about 

 seven, prominent, angular, radiating ribs on each side the mesial fold ; mesial fold deep, wide ; entire sliell 

 crossed by close, waving, erect lamina?. 



This most beautiful Spirifer is distinguished from the other species by the singular, scale-like sculptur- 

 ing of tlie surface, from which it derives its name. Length seven lines, width one inch three lines. 



Ctbtia linguifera. 31' Coy. 



Spirifera ostiolata. Phil. Pal. Fos. (omit Synonymes). 



Sp. Ch. — Subrhomboidal, gibbous ; cardinal area large, triangular, concave ; mesial fold wide, rotmded, 

 well defined, in old shells produced in front into a tongue-shaped process, without ribs on either valve ; ten 

 rounded, smooth ribs on each side the mesial fold. 



The shell to which I have given this name appears to me identical with that figured by Professor Phillips, 

 from the Devonian rocks, considered by him as the Spirifera ostiolata of Bronn and Schlottheim ; that shell 

 has, however, a narrow cardinal area, with parallel sides, and the beaks Incurved, approximate ; the present 

 species has, on the contrary, a very wide triangular area, and the beak of the dorsal valve is not incurved ; 

 there are also several minute distinctions between the species; I have given, however, the most striking 

 points. The lateral ribs are rounded and smooth, about ten or twelve or each side the mesial fold. I have 

 a very singular specimen from the Kildare limestone, which has twelve ribs on one side the mesial ridge, and 

 but six on the other ; the mesial fold is very prominent, and rounded, the surface, particularly in old shells, 

 is marked by irregular, transverse Unes of equal growth. Length one inch, width one and a quarter inches. 



CyRTIA MESOGONIA. M'Coij. (PL XXII. fig. 13). 



Sp. Ch. — Semicircular, gibbous; surface smooth ; cardinal area wide, concave, triangular ; cardinal angles 

 acute ; mesial ridge very prominent, angular, both it and the angular mesial furrow without ribs ; eight or 

 nine strong, rounded, equal ribs on each side the mesial fold. 



This species is allied to the Spirifer distans, Sow., and the S. ostiolata, Phil., but is distinguished from 

 both by the very prominent, angular, mesial fold ; S. distans has also the mesial hollow ribbed, while it is 

 smooth in the present species. Length one inch, width one inch five lines. 



Ctrtia nitda. Sow. sp. 



Spirifer nudus. Sow. Geol. Trans. — Spirifera nuda. Phil. Pal. Foss. 



Sp.Ch. — Subrhomboidal, gibbous; ventral valve semicircular, width twice its length; cardinal angles 

 obtusely rounded ; cardinal area wide, curved, triangular ; mesial fold wide, rounded ; one or two obtusely 

 rounded ridges on each side ; surface with obsolete lines of growth. 



This obscurely marked species is in length seven hues, width ten Hnes. 



Ctrtia Semicircularis. Pliil. sp. 



Spirifera semicircularis. Phil. Geol. York. 

 Sp. Ch. — Front semicircular, width double the length ; cardinal area variable in width ; about four smooth, 

 radiated ribs are raised with the mesial fold, and there are about fomteen on each side of it. 



This shell is alHed to tlie S. distans, but is at once distinguished by the ribs on the mesial elevation. This 



2 M 



