214 



PEOCEEDINGS OP THE GEOLOGICAL SOCIETY. 



essentially characterize the lower members of the Carboniferous 

 group : such are Ilypodema and SyringotTvyris, neither of these 

 appearing in oldor strata. 



The spocific development of Productus has no precedent or parallel 

 in any other group of British strata. 44 species occur in the deposits 

 from the Calciferous Sandstone to the Lower Coal-measures, 5 species 

 in the Calciferous series, 16 in tho Lower Limestone Shale, 41 in 

 tho Carboniferous Limestone, 7 in the Yoredalo, 5 in the Millstone 

 Grit, 8 in the Lower Coal-measures, 1 in the Middle Coal-measures 

 (P. scabricidus), and none in the Upper Coal-measures ; the genus 

 (but no known Carboniferous species) passes to the Permian rocks, 

 and is represented by P. liorridus, its last appearance 



Tho genus Spirifera attains its highest development in this 

 horizon also ; 30 species range side by sido by with the Producti ; and 

 it is well to state also their numerical value in the several horizons : 

 Calciferous Sandstone 3 species, Lower Limestone Shale 17, Carbo- 

 niferous Linicstono 30, Yoredalc rocks 6, Millstono Grit 4, Lower 

 Coal-measures 4. 2 of the 30 species of Spirifera aro Devonian, 

 >S^:>. lineata and tip. Urii ; thus 28 species are new to Britain ; and 

 no less than ] 85 species (British, European, and American) have been 

 described. The Rhynchonellce of our Carboniferous rocks number 

 21 out of the 30 European species ; and 18 of them are now; the 

 3 derived from the Devonian aro II. pleurodon, li. pugnus, and 

 jR. reniformis. 



The gonus Terebratula begins here to be numerically abundant, 

 no species being known in the Silurian strata, and the Devonian 

 rocks yielding only 4 species, whilst 7 species are Carboniferous. 

 The great development of this genus in the Jurassic rocks surpasses 

 that of all other Clistenterata ; in our own area they apparently 

 nearly died out or migrated after the Carboniferous epoch, none 

 occurring in the Trias. The genus Athyris ranges from tho Cal- 

 ciferous Sandstones to tho Lower Coal-measures ; A. ambigua and 

 A. planosidcata arc tho only specios that transgress tho Carboni- 

 ferous Limostono. The genus Atrypa was formerly recognized as 

 a Carboniferous gonus with 20 species, which are now relegated to 

 fflvynchonella, Retzia, and Athyris, Camarophoria, with its 5 species, 

 belongs to the Carboniferous Limestone ; only C. crumena passes to 

 the Permian, omitting the 5 intermediate stages or horizons. 

 Chonetes, only in ono instanco (under tho species hardrensis), ranges 

 above tho Carboniferous limestone into the Lower Coal-measures, 

 tho whole 15 spocies being otherwise confined to tho limestone 

 and tho shale bolow. 



Tho significance or importanco of Productus as a Carboniferous 

 genus cannot be overlooked when determining through its spocies 

 definite horizons in these rocks. It is ubiquitous ; in no region on 

 the globe, where tho Carboniferous rocks aro developed, do we not 

 find this characteristic shell and in vast abundance — in the Polar 

 regions, Australia, Now Zealand, Van Diemon's Land, India, Ame- 

 rica (in 15 States), throughout Europe, and in Africa. 



The Carboniferous Erachiopoda consist of 20 genera and 175 



