CARBONIFEROUS FOSSILS OF IRELAND. 141 



Tills is a very small species, rarely attaining three-quarters of an inch in length ; it has been taken for the 

 young o^ Martinia (fJabra, but is distinguished by its produced front, the smallness of its beaks, and the want 

 of the mesial sulcus in the larger valve. Mr. Sowerby's figure shews no cardinal area, but the shell, which I be- 

 lieve to be identical, as well as Professor Phillips's, has a distinct one resembling that of the M. obtiisa. Length 

 eight lines, width nine lines. 



Martinia protensa. PIdl. sp. 



Spirifera protensa. Pliil. Pal. Foss. 



The few imperfect specimens which I have referred to this species, appear to me to differ from the S. 

 obtusa. Sow., only in the stronger striatiou of the cardinal area, a character which depends very muchon the 

 state of preservation of the shell. I ha^•e not obserA^ed the radiated surface. 



Martinia RHOMBOiDALis. M'Coy. (Pl.XXII.fig.il). 



Sp. Ch. — Rhomboidal, gibbous, length and width equal; cardinal angles rounded; cardinal area very 

 small, triangular ; beaks small, incurved ; mesial fold very prominent, narrow, rounded ; mesial sulcus deep ; 

 sinus in the margin large, linguiform; surface radiated with numerous, obtusely-roiuided, nearly obsolete 

 ridges. 



This species is allied to the »S'. protensa, Phil., from which it differs in the length being equal to the width, 

 and in the very small size of the cardinal area ; from the A. plebeia. Sow., it differs in the great size of the me- 

 sial fold, and in the radiated surface. Length eight lines, width seven and a half lines, depth six lines. 



Martinia strigocephaloides. MCoy. (PI. XXII. fig. 8). 



Sp. Ch. — Suborbicular, gibbous; dorsal valve produced into a lengthened, acute beak; cardinal area nar- 

 row, acute, angular ; no mesial fold ; surface marked with regular, concentric lines. 



This remarkable shell seems to conduct to the Pentamerce by means of Striffocephalus, the external form of 

 which it exactly assumes, the gradation being rendered perfect by the present shell, on the one hand, and by Pro- 

 fessor Phillips's Striffocephalus brevirostris on the other, so like, indeed, are the two shells, that were it not that 

 the Devonian shell has a smooth surface, and this a concentrically lined one, tliey might be taken for the same 

 species. Professor Phillips's shell, however, has the same internal structure as the Strig. Burtoni, it, therefore, 

 belongs to the same genus, while my species has the internal structure of the group in which I have placed it. 

 As this species, from its external characters, appears to form the passage from the complex DeltheridcB or true 

 Spirifers to the more simply formed Pentamerida of the older rocks, it may be interesting to detail, as far as 

 I know, its internal anatomy. The dorsal or beaked valve exhibits, at about one-third of its length from the beak, 

 Fig. 23. the cicatrices of the upper pair of adductor muscles ; these are remarkably small, of a lengthened, 

 .-•' _ \ narrow, oval figure, the depth of each equal to about its own diameter ; they are separated from each 

 /linlflili'' other by a short, thin, shelly septum, which doesnot extend farther from thebeak than the muscles 

 ^'lfti4<lll'i ■"'^i'^'ii'^ separates. In the annexed cut (fig. 23) I have figured those parts of the natural size, toge- 

 \W^r^lw ther with the palleal impression, or attachment of the mantle of the animal. The ventral or smaller < 

 "'^^^rnnr:^'' valve has its beak divided by a thin, shelly septum, which, extending a short way towards the 

 margin, serves to separate the origin of the upper pair of adductor muscles ; the cicatrices produced by the 

 origin of those muscles in the ventral valve are much smaller, even than the origin of tliose in the dorsal valve ; 

 they are of the same lengthened shape, but each terminated at the end nearest the beak by a small, deep fora- 

 men, which serves for the insertion of the principal tendon ; they form little, sharp tubercles on the cast. The 

 spiral appendages arise each from a broad, flattened, triangular process, theu- bases being placed so as to diverge 



2 N 



