THE BRITISH FOSSIL BRACHIOPODA. 249 



typical specimens, but we also meet with a number of ' intermediate forms,' specimens 

 ' not well marked,' with the specific characters ill-defined, and approaching an allied 

 type. Unfortunately these specimens are, as a rule, rejected by collectors as troublesome 

 and unworkable, and are therefore stowed away in boxes amongst the duplicates and lost 

 sight of. This is a most regretable custom, by which we have already lost a mass of 

 valuable material. The value of the work of separation of species and the discrimination 

 of their special characteristics are not likely to be underrated by the geologist and 

 naturalist, but the discovery of their relations to one another and the determination of 

 the positions they have occupied in the development of the great life-groups is likewise a 

 noble work, and a work not only of profound interest to the biologist, but one that we 

 may also hope to be of great value even to the geologist in determining the relative ages 

 of rock-beds. 



" The acquisition of large numbers of Brachiopods from the rich collecting-grounds of 

 Upware and Brickhill has furnished us with unusually good opportunities for working 

 out the meaning of these variations amongst the species of Terebratula, &c. At Upware 

 many of the species are well defined, as Terehratula TJpwarensis, Waldheimia Woodwardi, 

 Terebratella Met/eri, and Terebratella Davidsoni ; but some species are so freely connected 

 that an ordinary small collection cannot, to our satisfaction, be completely separated out 

 into its several species. Such are, for example, Terebratula depressa, T. pralonga, and T. 

 microtrema. But it is at Brickhill that these intermediate forms are most conspicuous and 

 important ; from this locality the Woodwardian Museum has accumulated upwards of 

 15,000 specimens of Brachiopoda, and from these I have selected a series of specimens 

 and arranged them upon tablets, to show the relations of the species to one another, as 

 shown by intermediate connecting forms in the following manner : 



" Genus — Terebratula. 

 " Terebratula Cantabrigiensis, Walker. 



7 * ( -^cyrta, Walker. 



— depressa < ■ ?■ , W n 



I ( —^unijuicata, Walker. 



— Seelegi, Walker. 



V o ( -*■ Dallasii, Walker. 

 * I 9 ' ' \—^Lankesteri, Walker. 



— microtrema, Walker. ( -f/™™> ^ey™. 



(. ...Me yen, Walker. 



— Moutoniana, d'Archiac. 



— sella, Sow. 



— Tornasensis, d'Archiac. 



\ 



— Ujncarensts, Walker. 



