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PROCEEDINGS OP THE GEOLOGICAL SOCIETY. 



[Mar. 6, 



Myoch. costata, and T. Jieliciniis — are undoubtedly common to the Upper 

 Limestone and the TuUyconnell deposit, though likewise common to 

 the inferior beds ; and, had they occurred alone or with other species 

 also characteristic of the higher portion of the series, their evidence 

 woidd then have been more in favour of Prof. King's suggested 

 classification. But, as they are associated with other species, such 

 as Stem. MacJcrothi, Mis. Leighi, and Mil. pusilla, which, in all dis- 

 tricts where the succession of beds has been determined, are confined 

 to the lower and middle parts of the series, — and as they are them- 

 selves among the most common species of the lower beds in some 

 localities, it would appear pretty certain that the balance of palseon- 

 tological evidence supports a classification of the Cultra and Tully- 

 connell beds with the inferior rather than with the superior mem- 

 bers of the Permian series. 



§ IX. The Zechstein. — Timewill not allow myattempting compari- 

 sons with the groups of species found in the Zechstein of Germany; and 

 to do so would require a wider scope than the limit of this paper 

 permits. Comparisons, however, of this and of the other groups of 

 species found in the Permian strata of Britain with those of the 

 Zechstein would most assuredly bring to light many interesting facts 

 connected with the distribution of marine life, in time and space, 

 during the Permian era. The intimate relation which exists between 

 the marine fossils of the Permian rocks of Britain and Germany 

 proves them to be the remains of one fauna peopling the same geo- 

 graphical province or area of deposition. And to trace the various 

 phases in the histoiy of this fauna, its peculiarities of distribution 

 in space and in time, its development, and manifold relations, will 

 certainly be the work of some palaeontologist when our knowledge 

 of it and the strata containing it becomes more advanced. 



§ X. Conclusion. IHstributionofthe Permian Fauna in Time. — After 

 the deposition of the Lower Limestone and during that of the Small- 

 grained Dolomite, it would appear as if there had been a total with- 

 drawal of species from the South Yorkshire area. During the same 

 period in Durham the Permian fauna was at its maximum. Thus 

 we have another most remarkable instance of local difference in the 

 geographical distribution of Permian species. 



This exodus of species was in most cases permanent. Only two 

 are known to return during the deposition of the Brotherton Beds. 

 Others may certainly be undiscovered ; but so far as we know Axinus 

 dubius and Myalina Hausmanni, accompanied by one, or perhaps 

 two, species of AJgce previously unknown, are the only ones that 

 revisit the South Yorkshire area. During the early part of the same 

 period a few other species were associated with these in the nearly 

 adjoining region of Durham. But the Durham fauna, like that of 

 Yorkshire, was greatly reduced in number, both specifically and 

 individually, compared with its development in the preceding epoch. 

 Out of its 118 Shell-limestone species only 22 reappear in the Upper 

 Limestone, 6 new species appearing along with them. In the highest 

 portion of this member (at Roker and Hartlepool), the only species 

 that occur are the two Conchifers found in the Brotherton Beds, and 



