CARBONIFEROUS FOSSILS OF IRELAND. 131 



Spirifeba Crispa. So/v. 



Spirifer crispus. Sow. Sil. Syst Delthyris erispus. Dal. Act. Holm. 



Sp. Ch. — Semicircular, gibbous; lilngc-line equal to the widtli of tlie slicll; cardinal area large; three or 

 four large plaits on each side of the mesial ridge ; surface crossed by concentric, imbricating laminse of growth. 



This beautiful shell is alUed to the C. insculpta, Phil., and S. octoplicata, Sow. Length six lines, width 

 nine lines. 



Spirifera decemcostata. M'Coy. (PL XXII. fig. 9)- 



Sp. Ch. — Semicircular, gibbous, smooth, twice as wide as long; front rounded; sides suddenly attenuate, 

 cuspidate ; mesial lobe large, round, projecting, with five large, rounded ribs on each side, leaving a broad space 

 at the cardinal angles smooth, or only striated transversely. 



This species is so very distinct from every other Spirifera with which I am acquainted, that it would be un- 

 necessary to point out any particular difference ; the whole surface is smooth, except the cuspidate sides, which 

 are marked with strong lines of growth. 



& 



Spirifera disjuncta. Sow. 



Spirifer disjunctus. Sotc. Geol. Trans Spirifer disjuncta. Phil. Pal. Fos. 



Sp. Ch. — Semicircular ; twice, or twice and a half as wide as long, gibbous ; cardinal area broad, flat, 

 beaks remote ; mesial furrow strong ; surface with numerous, narrow, radiating ridges. 



This species is more gibbous and less transverse tlian the S. attenuata, and has a much wider cardinal 

 area. Length one inch, width two inches three lines. 



Spirifera Extensa. Sow. 



Spirifer extensus. Sow. Geol. Trans. 



Sp. Ch. — Width five times the length, convex; cardinal area narrow, with parallel sides; cardinal angles 

 very acute ; mesial fold prominent, defined ; surface radiated with narrow, rounded, equal ribs. 



A few imperfect specimens of this species have occurred; it is allied to the S. ainvoluta, Phil., but is dis- 

 tinguished by its more numerous and slender radiating ridges. Length six fines, width two inches six Unes. 



Spirifera furcata. M'Coij. (PI. XXII. fig. 12). 



Sp. Ch. — Semicircular, gibbous; length three-fourths the width ; sides rectangular; mesial fold defined, 

 prominent, rounded, with about six thick, rounded ribs, two of which reach the beak; sides with about five 

 strong, radiating ridges on each side, near the beak, each of which branches into two or three strong, rounded 

 ribs, as they approach the margin. 



Distinguished from Sp. {Brachythyrls) dupUcicosta, Phil., by the long hinge-line and cardinal area, 

 which place it in the present genus as strictly defined, and by the greater thickness and less number of radiat- 

 ing ribs ; and from the S. laxa, Portk., by the strongly ridged mesial fold. Length eleven fines, widtli four- 

 teen lines, depth six lines. 



Spirifera fusiformis. Sow. 



Spirifera fusiformis. Phil. Geol. York. 



Sp. Cli. — Transversely elongate ; width nearly four times the length ; sides rapidly tapering, conical ; 

 mesial hollow wdde, smooth ; mesial ridge with three ribs ; eight round, smooth ribs on each side the mesial fold ; 

 it has a wide and greatly hollowed cardinal area, the beaks are much incurved and approximate ; the sides 



