r from the Oarboniferous Limestane. 427^ 



length of the combined mesial portion, but of slightly greater 

 width : two mesial septa of entering valve narrow, scarcely 

 one-third the depth of the mesial septum of the receiving 



.valve; anterior broad ends very obliquely truncated, but 



, reaching rather less than half the length of the valve. 



' Average width 1 inch 2 lines, proportional length of enter- 

 ing valve -^jf-Qy length of hinge-line y^/^, length of re- 

 ceiving valve valuing from -fi^^-^ to |gg, height of cardinal area 

 varying from y^^^^ in the former to yY^ in the latter, width of 



: mesial ridge and sinus in the front margin y^^^, depth of en- 

 tering valve j^-Q to -^-^Q, depth of receiving valve y^^°^ to -^jfj^. 



Some of the specimens of this species so nearly resemble 

 Spirifers, that it was not until I made sections in various direc- 

 tions of several specimens, demonstrating the invariable presence 

 of the two narrow longitudinal subparallel septa in the entering 

 valve, and the wide, extremely long mesial septum in the re- 

 ceiving one, with its internal divaricating portions flanking the 

 triangular opening in the cardinal area, perfectly agreeing with 

 Pentamerus, as well as the absence of spiral appendages, that I 

 was convinced of its true genus. I have had the pleasure of de- 

 monstrating those specimens to M. de Verneuil, who, like myself, 

 was fully satisfied of their being true Pentameri, and saw in them 

 the first example of the genus in carboniferous rocks {the. Pen- 

 tamerus Sella and P. plicatus of Kutorga being obviously Came- 

 rophorici). 



Not very uncommon in the impure lower carboniferous lime- 

 stone of Kendal, Westmoreland. 



{Col, University of Cambridge.) 



«js ^xt :^fioii 



bff?^ Leptcena {Chonetes) polita (M'Coy). ' n^it 



Desc. Transversely fusiform ; hinge-line exceeding the width of 

 the shell, forming narrow semicylindrical convoluted ears, each 

 bearing four or five small spines ; receiving valve nearly hemi- 

 spherical, very gibbous in the middle and towards the beak, 

 which is large, inflated, and seems considerably to overhang 

 the hinge-line from the abrupt contraction of the ears, which 

 are separated by an abrupt curve from the steeply sloped 

 , i^ides ; front margin slightly elevated into a broad wave ex- 

 . tending its whole width, no mesial furrow; entering valve 

 almost as concave as the receiving one is convex; cardinal 

 .area about ten times wider than high; substance of the shell 

 , jthick ; external surface of both valves perfectly smooth, or 

 g'y^der a strong lens, with minute concentric striae of growth 

 ^^ear the margin ; internal cast of receiving valve marked with 



