CARBONIFEROUS FOSSILS OF IRELAND. I45 



Brachythybis hemisphyErica. M'Coy. (PI. XIX. fig. 10). 



Sp. Ch. — Orbicular ; dorsal valve hcmisplierical ; ventral valve flat, slightly convex towards tlie beak ; car- 

 dinal area an equilateral triangle ; mesial fold broad, flat ; about ten broad, flat, entire ribs on each side. 



The only species this at all resembles is the S. planata, Phil, from which it is easily distinguished by the 

 peculiar proportions of the cardinal area and dorsal valve. In some specimens the mesial fold is smooth, in 

 others obscurely divided by two or three lines, but in all the specimens it is perfectly flat, and not raised above 

 the surface. Length one inch, width the same. 



Brachythyris integbicosta. Phil. sp. 



Spirifera integricosta. P/iil. Geol. York. 



Sp. Ch. — Transversely oval, gibbous, mesial fold, defined on each side by a furrow deeper than the rest; 

 ribs very prominent, rounded, entire ; beaks closely approximate. There are about ten very prominent, round 

 ribs on each side the mesial elevation, which latter is prominent, well defined, and formed by the elevation of 

 three of the ribs, slightly flattened on their summits. The beaks are nearly in contact, the cardinal area con- 

 sequently narrow, much curved. I have seen fragments of a species closely allied to this, but having only 

 half the number of lateral radiations, the spaces between them equal to their breadth, and the cardinal area 

 much shorter. The B. integricosta usually measm-es one and a-quarter inches in length, and one and a-half in 

 breadth ; depth three-fourths of an inch. 



BrACHYTHYRIS LINGUIEERA. Phil. SP. 

 Spirifera linguifera. Phil. Geol. York. 



Sp. Cli. — Rotundato-quadrate, gibbous; mesial fold very prominent, rounded, smooth; about ten broad, 

 faint ribs on each side near the margin ; length nearly equal to, or slightly exceeding, the width ; depth equal 

 to the length of the ventral valve. 



This is the most aberrant species of the genus, leading to Martinia, or the smooth Spirifers ; we accord- 

 ingly find the lateral ribs exceedingly obscure, even at the margin, and almost totally effaced near the beak ; 

 assuming much of the character of the true Martinia. The mesial elevation and corresponding hollow are, in 

 general, free from sulci ; the cardinal area is very short ; the beaks tumid, much incurved, but not close. Length 

 one inch four lines, width one inch three lines. 



BrACHYTHYRIS OVALIS. Phil. SP. 

 Spirifera ovalis. Pliil. Geol. York. 



Sp.Ch. — Longitudinally oval, beaks approximate; cardinal area narrow, triangular; seven or eight ob- 

 tusely rounded ribs on each side the mesial fold, which is prominent, rounded, smooth, and without plaits. 



This is one of the very few Spirifers in which the length exceeds the breadth ; in the present species the 

 length exceeds the width by only one-twelfth, yet it nevertheless gives a remarkable outline to the shell, 

 which is commemorated in Professor Phillips' specific name ; it is, in fact, almost perfectly oval, the long axis 

 being in the direction of the length of the shell ; the mesial fold is broad, rounded, and perfectly smooth. 

 Length one inch, width eleven lines, depth seven lines. 



BrACHYTHYRIS PINGUIS. SoW. SP. 

 Spirifer pinguis. Sow. Min. Con. 



Sp. Ch. — Globose, beaks very approximate ; mesial fold round, prominent, distinctly defined, and without 

 plaits; length and width equal, depth exceeding the length of the ventral valve. 



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