CARBONIFEROUS FOSSILS OF IRELAND. 117 



ments of the principal pair ofadductor muscles, form two hemispherical smooth cicatrices (a a fiw. 12), about half the 

 size of those in the dorsal valve; they are nearly half their diameter dis- Fig. 12. Fig. 13. 



tant from the hinge-line ; considerably anterior to them are the two elon- 

 gated, pear-shaped origins of the lesser pair of adductors (b b) ; they 

 differ from those in the dorsal valve in being smaller, and having their ItJ^^ 

 attenuated extremities directed anteriorly instead of posteriorly ; they ' 

 are divided by a thin, shelly septum ; figure 13, A A, shews the perfect 

 form of the cardinal teeth in the next species. 



Leptagonia analoga. Phil. sp. 



Producta analoga. Phil. Geol. York Leptsena analoga. Sow. Geol. Trans. 



Sp. Ch. — Rostral portion flat, slightly convex in the middle; about fourteen irregular, concentric rugae, 

 crossed by rather coarse, straight striae from the beak ; front short, flattened in the middle. Length about one 

 inch, width two inches. 



This species has been well separated from the Producta depressa, Sow., by the accurate author of the 

 Geology of Yorkshire, although many observers still confound the two. It differs from the Producta depressa 

 in having the flat part of the valves much less depressed than in that species ; the concentric rugae are double 

 the number, and the size nearly twice the usual dimensions of the Producta depressa of the Silurian rocks ; the 

 front, or deflected portion, is flattened, or even concave in the middle, and in well preserved specimens extends 

 beyond the hinge-line, forming smooth, rounded ears ; the concentric wrinkles are rounded, irregular ; the two 

 valves are aUke ; the cardinal area about a line in width, transversely striated ; the triangular foramen is 

 large. 



Leptagonia depbessa. Sow. sp. 



Producta depressa. Sow. Min Con. — Leptsena depressa. Sow. Sil. Res. 



Sp. Ch. — Subquadrate; flat part of the valves very much depressed ; about ten irregular concentric wrin- 

 kles, crossed by straight, radiating striae. 



The specimen above described is the first I have known from the mountain Hmestone. Professor Phillips' 

 specimen, to judge from the figure, looks more like the L. rugosa. The present species is smaller, and nar- 

 rower in proportion than the foregoing ; the flat portion of the valves is also much more depressed, so much 

 so, that the angle which separates it from the descending front forms a prominent border to it all round ; 

 the front is flattened in the middle, and at the sides, thus giving a quadrangular contour to the shell. Length 

 five lines, width seven lines. 



Leptagona multieugat^. M'Coy. (PI. XVIII. fig. 12). 



Sp. Ch. — Top of the upper valve flat ; closely striated, with about twenty- two concentric rug^, which 

 frequently unite in pairs as they approach the hinge-line ; hinge-line straight, equal to the breadth of the shell ; 

 length, three-fifths the breadth. 



This shell, as well as the Producta analoga of Professor Phillips, has been frequently confounded by 

 geologists, with the L. depressa of the Silurian rocks ; this latter, however, I have seen very rarely in undoubted 

 mountain limestone, nor do I know that either of the former have been found in any of the Silurian range. 

 The present shell is distinguished from the nearly alhed species, L. depressa, L. analoga,^vAL,. tenuistriata, 

 by having the top of the upper valve perfectly flat, neither sensibly convex nor concave, as in those species. 

 The concentric furrows are greatly more numerous in the present shell ; these in Leptcena analoga are about 

 tliirteen or fourteen, in Leptana tenuistriata twelve, and in L. depressa muchless. Breadth of the shell about 

 an inch. 



2G 



