'FOSSIL LAMP-SHELLS. 233 



conchological hedgehog), or the well-known Pro- 

 ductiis horridus of the Permian rocks — the latter 

 found in good condition near Tynemouth. Another 

 feature about the valves of the ProditcUis 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 Productidcs 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 



