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been decvoasincf in number to the present period. They might 

 leave out of the question the species, for they varied so little that 

 it was often very difficult to trace really good distinctive characters 

 between them, it was different with genera as they were, or 

 should be, founded on much greater and permanent distinctions. 

 Thus, for example, the family of Sjnriferidce included genera . 

 characterised by calcified spiral lamina for the support of the 

 brachial appendages, and however varied they might be tbey always 

 retained the distinctive characters of the group from their first ap- 

 pearance to their extinction. The Brachiopodist laboured under the 

 difficulties of not being able to determine what are the simplest, or 

 which are the highest, families into which either of the two groups 

 of his favourite class was divided, so far, then, he was unable to 

 point out auy evidence favouring progressive development in it, 

 But, confining himself to species he had often before him great 

 varietal changes, so much so, as to make it difficult for him to 

 define the species ; and it led him to the belief that such groups 

 were not of independent origin, as was universally thought before 

 Darwin published his great work on the origin of species. But in 

 this respect tlie Brachiopoda revealed nothing more than other 

 groups of the organic kingdom. All the Produdidoi had their 

 permanent and constant characters, and so on. It would appear 

 that the earliest forms among the Brachiopoda are referable to the 

 division Tretenterata, which included the genera lingulella, lingula, 

 discina, and obolella. Of these, lingula and discina only had lived 

 on with but slight modifications in external shape, during the 

 entire sequence of geological time, and they were still represented 

 by several species, but in rocks, somewhat later in age, the 

 Menevian group, or lower lingula flags, there occurs a sx^ecies of 

 orthis, the first representative, as far as they were aware, of the 

 division Clistenterata, but there was not the slightest evidence 

 that orthis was ever derived from any of the four genera of 

 Tretenterata above named. Since that period both divisions 

 continued to be represented, without ever showing a tendency to 

 pass one into the other. Now, although certain genera, such as 

 Terebratala, Splrifer, Bijnchonella, Crania, Discina, and Lingula, 

 had enjoyed a very considerable geological existence, and had 

 varied very little since their first appearance, and might be looked 

 upon as among the earliest Brachiopoda, there were genera such 

 as String ocephalus, Uncites, Porambonites, Konincldna, &c., which 



