CARBONIFEROUS FOSSILS OF IRELAND. 125 



tlic width. I have never seen the O. Kellii more tlian two inches in length, while the O. crenistria is fre- 

 quently double that size, and is almost always larger than the former species. The striation is so variable in 

 those shells, according to the state of preservation of tlie surface, that it Is of little use in specific distinctions ; 

 the strlre, however, of the O. Kellii, M'Coy, although resembling In character those of the O. crenistria, 

 Phil., arc usually much liner, closer, and more nearly equal, than in that species. Length one inch four lines, 

 width one inch eight lines. 



Oethis latissima. M'Coy. (PI. XX. fig. 20). 



Sp. Ch. — Twice and a half wider than long, depressed, convex near the beak; margin slightly inflexed; 

 cardinal angles rounded ; surface regularly and closely marked with fine, rounded strina ; internal Impression 

 large, formed of two lobes on each side, the anterior of which Is dilated, and spatulate at the tip, that nearer the 

 beak suddenly pointed ; central septum extending only as far as the lateral impressions. 



This is the widest species of Orthis with which I am acquainted ; It is convex only near the beak, and the 

 long ears are rounded and slightly turned up as in the Lejdcena latissima; there is a narrow, inflexion of the 

 margin ; the radiating strlee are exceedingly fine, close, equal, rounded, and smooth ; the Internal supports are 

 very large, forming a double lobe on each side. Length eleven lines, width two inches two lines. 



Okthis longisulcata. Phil 



Orthis longisulcata. Pliil. Pal. Fos. 



Sp. Ch. — Transversely oval, rather more than twice as wide as long, depressed; surface radiated with very 

 fine, divaricating striae, increasing in number towards the margin, and In old specimens decussated by imbri- 

 cating lamina of growth ; cardinal teeth very long, straight, diverging. 



This species is allied to the 0. interlineata, but is more finely striated ; the long, straight teeth distinguish 

 it from any of the other species. Length nine lines, width one inch seven lines. 



Orthis orbicularis. Sow. 



Orthis orbicularis. Sow. Sil. Syst. 



Sp. Ch. — Orbicular, depressed; beak small; hinge-line nearly equal to the width of the shell; dorsal valve 

 convex, the other flattened, with a wide mesial hollow ; both valves finely striated. 



I have not seen the Internal structure of this species, which is almost necessary for its recognition. 



Orthis papilionacea. Phil. sp. 



Spirifer papilionacea. Phil. Geol. York. 



Sp. Ch. — Width rather more than twice and a half the length; front deflected In old specimens; surface 

 covered with exceedingly fine, undulating, equal striae ; cardinal area narrow, rhomboldal, transversely striated. 



This beautiful species with age acquires nearly the size of the Producta i/igantea, and nearly the same 

 form, in which state it has, perhaps, been ranked with the P. cojtioides. When young, however, it is flat, 

 transversely elUptical, very wide, and with very acute cardinal angles. 



Orthis parallel a. PJdl 



Orthis interlineata. Sow. (pars) Orthis parallela. Phil. Pal. Fos. 



Sp. Ch. — Longitudinally ovate, depressed; surface with strong, alternately larger and smaller, divaricating, 

 angular strlas, doubling In number as they approach the margin ; cardinal teeth lengthened, slightly curved, 

 approximate at their tips, enclosing two long, tongue-shaped impressions. 



This species is very distinct from the O. interlineata, both in form and internal structure; it approaches 



2 I 



