1864.] TATE CEETACEOITS ROCKS OE IRELAND. 39 



C. cassis, D'Orb., and some others, but is easily distinguished by its 

 chain-like punctations in the narrow sulci between the flat and broad 

 longitudinal ribs. It is closely allied to C. ArcJiiaciana, D'Orb., from 

 which it is distinguished by the absence of the fine strise upon the 

 ribs, which characterize that species. There is also a marked diifer- 

 ence in the form of the punctations ; in C. catenata they are elliptical 

 and large, in G. ArcJiiaciana minute and circular. C. catenata is 

 also a much larger and more globose shell. 



The cast shows the broad flattened ribs, which enable one to dis- 

 tinguish it even in that condition from C. cassis, C. incrassata, and 

 others. 



Dimensions. — Length |- inch ; height of last whorl | inch. 



Locality. — This species is not uncommon at Kilcorig, Lisbuni, in 

 the " flinty flag" of the White Limestone (LTpper Chalk). 



9. Plicattjla DELTOiDEA, spec. nov. PI. III. figs. 5a, 5h. 



SheU ovato-triangular, oblique, very depressed, nearly equivalve ; 

 superior valve nearly flat, inclined to convex, with numerous im- 

 bricated lamellse coincident with the contour of the valve ; inferior 

 valve slightly convex, ornamented with concentric lamellae, which 

 are produced into spines, the spines disposed in seven rays, with 

 one or two intercalated towards the margin. Adherent by the apex. 



Affinities and Differences.- — This shell in its depressed form is 

 allied to P. clatlirata, E. Deslong. ; but it differs from that species in 

 the character of its ornamentation. P. clathrata is furnished with 

 numerous radiating dichotomous ribs, which are not spinous. In 

 the character of the spinous rays of the lower valve, P. deltoidea re- 

 sembles P. radiola, Lam., and P. gurgitis, Pictet & Roux. Prom 

 these species it is distinguished by the absence of the rounded, very 

 slightly elevated, feebly spinous rays of the upper valve, and by being 

 depressed ; for in these species the superior valve is concave, and 

 the inferior very convex. 



Locality. — This species I obtained from the Glauconitic Sands at 

 Whitehead, during the construction of the raihvay. It is very rare. 



10. Caedittm: gibbosxtm, spec. nov. PL IV. fig. 6. 



Shell equilateral, oblong, compressed, remarkably inflated at the 

 umbones ; ornamented by about twenty flat radiating ribs ; the sulci 

 about equal in breadth to the ribs; interspaces between the ribs 

 crossed with transverse bars. 



The remarkably gibbous character of this shell is very distinctive, 

 and the oblong form further distinguishes it from any other species. 



Dimensions. — Length -j^ inch ; height -^ inch. 



Locality. — I am acquainted with only five specimens of this species, 

 all from the Zone of Exogyra columba of the Hibernian Greensand 

 of Colin Glen. 



11. Pecten GLAtrcoNETjs, spec. nov. PI, IV. fig. 5. 



Shell equivalve, equilateral, ovate-orbicular, slightly convex ; 

 ornamented with from fifteen to twenty convex and elevated radi- 



