22 THE INDIGENOUS FAUNA. 



On Varietal and Intermediate Forms amongst the species of 



Brachiopoda. 



It is a matter of general experience in working amongst the 

 more prolific families and genera of organic types that the bound- 

 aries of our recognised species are found to be most shadowy and 

 evanescent. In any particular species we have the well-marked 

 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 have 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 Terehratida Upwarensis, 

 Waldheimia Woodwardi, Terehratella Meyeri, and T. 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, prcelonga, 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 Brachiopods, and from these I have selected a 

 series of specimens and arranged them upon tablets, to shew the 

 relations of the species to one another, as shewn by intermediate 

 connecting forms, in the following manner: — 



