FOSSIL LAMP-SHELLS. 233 



conchological hedgehog), or the well-known Pro- 

 ducttis horridus of the Permian rocks the latter 

 found in good condition near Tynemouth. Another 

 feature about the valves of the Productus family is 

 that they are " auriculated," which means that the 

 shells are more or less drawn out on either side of the 

 hinge-line. The Productida have been extinct ever 

 since the close of the Primary or Palaeozoic epoch. A 

 microscopical examination of the shells of any species 

 of Productus would alone enable a student to identify 

 it, if only on account of the peculiar " canals " which 

 are present. 



Speaking of this group of fossils, Mr. Etheridge 

 says "The significance or importance of Productus 

 as a Carboniferous genus cannot be overlooked when 

 determining, through its species, definite horizons in 

 these rocks. It is ubiquitous ; in no region on the 

 globe, where Carboniferous rocks are developed, do 

 we not find this characteristic shell, and in vast 

 abundance in the Polar regions, Australia, New 

 Zealand, Van Dieman's Land, India, America (in 

 fifteen states), throughout Europe, and in Africa." 



The space in the hinge-line between the two 

 shells (deltidium) has to be taken into account in 

 the endeavour to identify species. This is largest 

 developed in Spirifera deltoidea of the Car- 

 boniferous limestone and is not an uncommon 

 fossil at Castleton, in the Peak District of Derbyshire, 

 surely, one of the most delightful for a young 



