from the Carboniferous Limestone. 423 



posterior third of its length, much more gently arched in the 

 anterior two-thirds, so that the anterior lobe projects much 

 from the front margin; mesial hollow deep, corresponding 

 ridge moderately prominent; radiating ridges very large, 

 thick, angular, three strongly marked on the mesial hollow, 

 of which the middle is much the broadest and most depressed 

 on the shell ; the two lateral are imperfectly and obscurely 

 triplicated towards the margin ; corresponding sulci on mesial 

 ridge faintly marked ; on each side are about five great an- 

 gular radiating ridges, some of which show a faint tendency 

 to imperfect division towards the margin ; the narrow flattened 

 sides, or cardinal angles, when preserved, show five or six very 

 much smaller obscure radiating ridges. Width about 2 inches 

 6 lines, proportional length of receiving valve y^^^, of entering 

 valve yY^, width of cardinal area y§^, depth of sinus in front 

 margin j'^^^, depth of both valves y'^'^j. 



This is allied to the S. triyonalis of Martin, but differs from 

 it by its abruptly narrowed and attenuated sides, and by its few 

 very large angular ridges occupying the body of the shell, and 

 the abrupt diminution in size of the five or six outer ridges on 

 each side. A very young specimen, 9 lines wide, has the three 

 ridges in the mesial hollow distinctly marked, but nearly as large 

 as the lateral ones, of which there are three or four great ones 

 on each side, but scarcely a trace of any additional ones on the 

 flattened cardinal angles, which are strongly striated parallel to 

 the margins. 



Rare in the carboniferous limestone of Derbyshire, but com- 

 mon in the Irish limestone at Ardagh. 



[Col. University of Cambridge.) 



Spirifera paudcostata (M'Coy) , 



Desc. Globose, or very broad, ovate ; hinge-line slightly shorter 

 than the width of the shell ; cardinal angles slightly obtuse, 

 sides and front moderately rounded, very obtuse from the 

 meeting of the valves at a large angle, front abruptly raised 

 into a wide semielliptical sinus. Entering valve evenly con- 

 vex, sides tumid, with six or seven strong, rounded, obtuse 

 simple ribs on each side ; mesial ridge broad, prominent, very 

 strongly defined from the beak, having three ridges about the 

 size of the lateral ones, each of which dichotomizes close to the 

 margin. Receiving valve very gibbous, semicircularly arched 

 from the beak to middle of front margin ; mesial sinus deep, 

 strongly defined from the beak, having at first three, subse- 

 quently six small obscurely marked ribs ; beak very large, in- 

 curved ; cardinal area moderately wide. Width 9 lines, pro- 



