ohopom the Carboniferous LimeatofieV^'^'^ 



tDj^ostepior third of its length, much more gently arched in the 



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



isifrom 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 



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



\rgular radiating ridges, some of which show a faint tendency 



* ^0 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 



^^ lines, proportional length of receiving valve -/q'^, of entering 

 ^jalve tVh, width of cardinal area yg^, dept^^of^s|n]ip, in fypnt 

 ^.margin ^'^%, depth of both valves ^%%. _^^^^^^ . ^^^ ^^^^^ 



This is allied to the >Si. 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 Derbyabire, but. com- 

 mon in the Irish limestone at Ardagh. ^ayij? iBaibiBa 

 i, {Col. University of Cambridge.) ...J?^^^- oU'sh lo 

 -OT > dibrff\i^W 

 e^vkv . Spirifera paucicostata (M'Coy). d-4 bnobioq 



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

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

 l>ii sides and front moderately rounded, very obtuse from the 

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

 t 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 

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

 3a strongly defined from the beak, having at first three, subse- 

 '^Inquently six small obscurely marked ribs ; beak very large, in- 

 ••^carved; cardinal area moderately wide. Width 9 lines, pro- 



