130 SYNOPSIS OF THE CHARACTERS OF THE 



Spirifera calcaeata. Sow. 



Spirifer calcaratus. Sote. Geol. Trans. — Spirifera calcarata. Pkil. Pal. Fos. 



Sp. Ch. — Nearly three times as wide as long, convex; cardinal angles attenuated, smooth; mesial furrow 

 strongly defined ; surface round, with numerous sharp, equal, radiating ridges, rarely branched ; those on the 

 mesial furrow smaller, and less prominent. 



This species is very common in the carboniferous slate of nearly every district in Ireland. It resembles 

 the S. attenuata of the limestone in many points ; but is more depressed, has the mesial fold more strongly de- 

 fined, and has the ridges more equal and sharply marked. Length seven lines, width one inch seven lines. 



Spirifera choeistites. Von Buck. 



Choristites mosquensis Sowerbii. Fisher. Oryct. Mos. 



Sp. C/(. — Subquadrangular, gibbous; cardinal area wide, flat; beaks incurved, remote; mesial fold shal- 

 low, rounded ; ribs numerous, depressed, branched, about nineteen on each side the mesial fold, which has 

 about ten of the same size and structure as those on the sides. Length slightly exceeding the width. 



This species is distinguished from the Spirifera hisulcata by the beaks being so far apart, and by the great 

 number of its lateral radiations ; from the Spirifera attenuata it is distingmshed by its length being about equal 

 to the width. I do not know that this shell has been before detected in Britain, unless, indeed, Mr. Sowerby's 

 Spirifera disjuncta may be looked upon as a variety of it. Professor Pliillips' Spirifera bisulcata is, perhaps, 

 also nearly allied to it. Spirifera disjuncta of the Devonian rocks is a wider shell. The specimens which I 

 have referred provisionally to this species have the mesial fold more strongly marked than in the foreign exam- 

 ples. Length one and a half inches, width two lines less, depth one inch. 



Spieifera clatheata. M-Coy. (PI. XIX. fig. 9). 



Sp.Ch. — Semicircular, gibbous; sides slightly cuspidate, twice as wide as long; mesial lobe narrow, 

 rounded, prominent ; ribs nimierous, branched, three or four on the mesial fold, and about sixteen on each side ; 

 whole surface reticulated with very minute, longitudinal, and transverse strlaj. 



This interesting shell might be mistaken for one of the shorter varieties of the S. attenuata, were it not 

 lor the minute reticulation of the surface. Length seven lines, width one inch two lines. Grows very much 

 larger than the specimen figured, equalling the Spirifera gicjantea in size, to which species it is closely allied ; 

 the rcticidation of the surface, however, seems peculiar. 



Spirifera convoluta. Phil. 



Spirifera convoluta. PJdl. Geol. York. 



Sp. C/«.— Fusiform, depressed, width about four times the length; cardinal area concave, striated across; 

 surface radiated with numerous, obtuse, rounded, smooth ribs, three of which are elevated to form the mesial 

 fold. 



This species is easily known from all otliers by its excessive width. Length eleven lines, width four inches. 



Spirifera costata. Sow. 



Spirifer costatus. Sow. Geol. Trans. 



See S. spcciosus. Mr. Sowerby's shell, and some of the Irish carb. slate specimens, have the ribs narrower, 

 and the intervening spaces wider, than in the Elfel specimens. 



