CARBONIFEROUS FOSSILS OF IRELAND. 129 



Spirifera attenuata. Sow. 



Spirifer attenuatus. Soic. ]Min. Con. — Spirifera attenuata. Phil. Geol. York. 



Sj). Cli. — Convex, width exceeding twice the length, cardinal angles attenuated; mesial fold rounded, 

 defined, cardinal area flat, with parallel sides ; beaks incurved, but not close ; radiating ribs numerous, some- 

 times simple, sometimes branched. 



This is, perhaps, one of the most difficult species to characterize, so numerous are its varieties ; the type of 

 the species is about three times as vfide as long, the depth equal to about the length of the smaller valve ; the 

 mesial ridge and corresponding hollow rounded ; the ridge defined on each side by a sulcus deeper than the 

 rest ; the surface covered with exceedingly numerous, thin, branched ribs. But the greater number of specimens 

 differ in .some particular or other. Thus, many specimens have no mesial elevation, in others the width is 

 little more than twice the length ; the depth varies greatly, and as to the radiating ribs we have every variety, 

 between those specimens having seventy very thin, branched, ribs, and those possessing but half the number of 

 thick, romided, simple, or undivided ribs. With respect to these latter varieties, I should remark, that some 

 authors have lately separated those with branched, and those with simjsle ribs, into two distinct species, but it Is 

 not by any means imfrequent to find the ribs on the dorsal valve branched, and those on the ventral valve sim- 

 ple, in the same specimen ; and where a large n amber of specimens can be compared, the passage from one ex- 

 treme to the other may In general be traced In the most perfect manner. In all these varieties the cardinal 

 angles, when perfect, are extended Into long, smooth spines. Length one and a quarter inches, width three 

 inches, depth one Inch. 



SpmrFERA BICARINATA. M'Coy. (PI. XXII. fig. 10). 



Sp. Ch. — Rhomboidal, width more than twice the length, very gibbous; sides cylindrical; mesial fold 

 wide, smooth, concave on both valves, bounded on both valves by two large, rounded keels ; about twelve 

 rounded, entire ribs on each side; cardinal area with parallel sides, very wide and hollow. 



This curious species Is easily recognized by the mesial fold being concave, and bounded by large keels 

 on both valves. Length eight lines, width one Inch six lines. 



Spirifera bisulcata. Sow. 



Spirifer bisulcatus. Soic. Min. Con. 



Sp. Ch. — Semicircular, gibbous; about ten or twelve strong, roimded, entire ribs on each side of the mesial 

 furrow, which Is strongly defined, round, and prominent, with slightly smaller, dichotomous ribs ; cardinal area 

 narrow, beaks almost In contact; width very little greater than the length. 



Although this is found in almost every list of mountain limestone fossils, I have found It exceedingly scarce 

 in every locality In Ireland, the fossils of which I have had an opportunity of examining, except the lime- 

 stone of Blackllon near Emilskillen ; the specimens most usually seen In Irish collections imder this name, 

 being Imperfect Individuals of Spirifera attenuata, having their cardinal angles broken off, so that the length and 

 width may be about equal. Besides having its length and breadth nearly alike, the present species may be dis- 

 tinguished from the Spirifera attenuata by the small number of Its simple, lateral ribs. Von Buch, and most 

 continental Oryctologists, consider this species as Identical with the Spirifer aperturatus of Schlottheim ; but as 

 Mr. Londsdale has already remarked, the beaks of the Spirifera aperturata are widely separated by an obtusely 

 triangular, cardinal area, while the present shell has the beaks in contact, and a cardinal area with parallel sides. 

 Professor Phillips's figure does not appear to belong to this species, It bears a closer analogy to the Spirifera 

 disjuncta, and to the next species. Length one Inch, width fourteen lines, depth nine lines. 



2K 



