2 DAY, Variation in a Carboniferous Brachiopod. 



possess the parallel dental lamellae which, together with 

 the reticulation, characterise McCoy's genus, Reticularia. 

 (A Synopsis of the characters of the Carboniferous Lime- 

 stone Fossils of Ireland, 1844, p. 143, and PI. XIX., 

 Fig. 15.) An enlarged view of the characteristic reticulate 

 ornament is given on PL 1, L. 



The whole question of the genetic relationships of the 

 Carboniferous Spiriferids is obscured by a complicated 

 synonymy, but still more so, as Buckman has shown 

 ("Brachiopod Homceomorphy": " Spirifer glabcr" Q.f.G.S., 

 1908) by heterogenetic homceomorphy. 



He shows, for example, that the "species" Spirifer 

 giaber is really a group name, and that under it several 

 different species and even genera have been included, 

 which have attained their very similar smooth appearance 

 "by the loss of different distinctive features, pointing to 

 polygenetic origins." 



It is therefore evident that a revision of the brachiopod 

 genera of the Carboniferous is very necessary, and such 

 revision has already entailed the institution of several 

 genera and species out of types formerly included under 

 one specific name. On the other hand there is always 

 the danger of carrying this process of revision to an 

 extreme, and needlessly instituting species upon what are 

 merely variations. 



In view of the above danger it was proposed to pursue 

 a careful investigation into the range and character of the 

 variation in one well-defined species of these Spiriferids, 

 with the object of indicating what range of variation 

 might be expected in other members of this family. 



The collection of shells upon which the following 

 results were based numbered one thousand individuals, 

 and was made from one spot in the limestone near Peaks- 

 hill Farm, Rushup Edge Valley, Castleton. 



