140 SYNOPSIS OF THE CHARACTERS OF THE 



either the Sjnrifera oblata or Spirifera ohtusa, with both of which authors have confounded it. Mr. Sowerby 

 lays stress on the mesial elevation being flattened in the middle ; it is, however, very frequently rounded, but is 

 always very wide and imdefined, in which it differs from the next species. Length one inch six lines, width 

 two inches six lines. 



Martinia mesoloba. Phil. sp. 



Spiriiera mesoloba. Phil. Geol. York. 



Sp. Ch. — Orbicular, depressed; mesial fold round, prominent, sharply defined on both valves; surface 

 smooth, slightly imbricated ; cardinal area very short, triangular. 



This species is nearly allied to the preceding, but when once seen will run no risk of being confounded 

 with it, or indeed with any other fossil 1 know. In outline it is nearly circular ; the valves are smooth, de- 

 pressed, and sharp-edged ; the beaks and cardinal area small ; the mesial fold is very peculiar, it is narrow, 

 rounded abruptly fi'om the depressed surface of the ventral, or smaller valve ; it is bounded on either side by an 

 impressed line, which renders it distinct up to the beak. Professor Phillips' figure is a very good one, and 

 shews the character of the mesial fold extremely well. The slightly imbricated lines of growth scarcely diminish 

 the smoothness of the surface. Length one inch, width one inch two lines. 



Martinia oblata. Sow. sp. 



Spirifer oblatus. Sow. Min. Con Spirifera glabra. Phil. Geol. York. (pars). 



Sp. Ch. — Gibbous, obovate, smooth ; mesial elevation square ; seldom distinct more than half way to the beak. 



The depth of this species exceeds half the width ; in young individuals there is no mesial elevation, or it 

 is but slightly marked on the edge of the shell, in old specimens it rarely extends within half the distance be- 

 tween the front and the beak ; In finely-preserved specimens there are traces of very obscure, lateral radiations 

 towards the margin. It is a local species in Ireland, but where it occurs it is usually very common. Length 

 two inches, width two Inches five lines. 



Martinia obtusa. Sow. sp. 



Spirifer obtusa. Soje. Min. Con. 



Sp. Ch. — Transversely oval, very gibbous; depth half the width; sides tumid; mesial furrow narrow, 

 rounded, forming a very deep sinus in front; beak of the dorsal valve, and cardinal area large, surface smooth. 



This species is thought by many authors to be Identical with the Spirifer glaber of the Mineral Conchology. 

 It appears to me, however, to be distinguished, as Mr. Sowerby observes, by the greater size of the beak of the 

 large valve, and by the greater depth of the sinus in the front, to which I might add, that the mesial ridge is 

 much narrower than in the former species, that the width is never so great In proportion to the length, and the 

 sides, which In Spirifera glabra are always more or less depressed, are In the present shell remarkably 

 tumid, or gibbous. Length one Inch five lines, width one inch nine lines. 



Martinia pnALiENA. Phil. sp. 



Spirifera phaltena. Phil. Pal. Fos. 

 Sj). Ch. — Twice as wide as long; beaks very prominent; mesial hollow very wide, rounded, bounded by 

 two prominent ridges ; surface marked with small, rounded, concentric ridges. Length six lines, width one inch 

 five lines. 



Martinia plebeia. Sow. sp. 



Atrypa plebeia. Sow. Geol. Trans. — Spirifera plebeia. Phil. Pal. Fos. 

 Sp. Ch. — Orbicular, subrhomboldal, very gibbous; front produced Into a tongue-shaped elevation; mesial 

 ridge wide, indistinct on the ventral valve ; beaks small, approximate ; surface smooth. 



