418 PROCEEDINGS OP THE GEOLOGICAL SOCIETY. [Mar. 14, 



system. As an instance, I may refer to the Trenton Limestone of 

 the palaeozoic basin of New York, which contains 250 species, only 

 6 of which are received from underlying strata*. On the most liberal 

 estimate, the Permian species of Britain do not form so large an aggre- 

 gate ; and on an estimate which appears more in harmony with truth, 

 they only number 136 species t- It will be seen, therefore, that Car- 

 boniferous rccurrents form about 11 per cent, of the British Permian 

 species. As yet, nothing is known of the recurrency of Carboniferous 

 species in the Permian faunae of Germany and Russia. It may be that 

 these faunse contain no recurrents from an earlier era, in which case 

 the general percentage of such recurrents in the Permian fauna at 

 large may not appear so great ; but from analogy we should imagine 

 otherwise. Our knowledge of the Russian fauna can at the best be 

 but elementary ; and we may rest assured that, notwithstanding the 

 valuable researches of Sir Roderick Murchison and his coadjutors in 

 Perm, there cannot but remain a large mass of information to work 

 out. It is possible to get more or less correct ideas of a life-group 

 by a cursory examination of the rocks containing it ; but to acquire 

 a fidl and complete knowledge demands long-continued researches $, 

 for such a knowledge is the aggregate of a multiplicity of details 

 which can only be collected by years of observation. 



In respect to the appearance of new generic types during the 

 Permian period, I may add that the only genera of Mollusca which 

 are apparently met with for the first time are Myoconclia and Thecl- 

 dium, which are likewise accompanied by the subgenera Monotis and 

 Aulosteges : the rest of the Mollusca belong to genera which appear 

 earlier. A genus of Crustacea (Palceocrangon) appears for the first 

 time, and, so far as is known, the only time. The Polyzoa §, Echino- 

 dermata, Zoophyta, and Hhizopoda are all of Carboniferous or more 

 ancient genera. It seems questionable whether any new generic 

 forms of Fish appear during Permian time ; certainly none in Britain. 

 Indeed the only class of animal life that assumes generic characters 

 which appear to be peculiarly Permian are the Rept'dia. Some stress 

 has been attached to the specific distinction of the Permian flora in 

 Germany from that in Britain ; and attention has been drawn to the 



* Quart. Journ. Greol. Soc. toI. xiv. pp. 344 & 345, also table, p. 420. 



t In this estimate of the Permian fauna and flora as distributed in Britain, the 

 number of species in each class are as follows : Heptilia 3, Pisces 17, Cephalo- 

 podon 1, Gasteropoda 20, ConcMfera 20, Pteropodon 1, Brachiopoda 17, Poly- 

 zoa 7, Crustacea 22, Annelida 4, Echinodermata 2, Zoophyta 2, Amorphozoa 5, 

 Rhizopoda 5. Between this enumeration and one based on the views of Prof. 

 King, there would be a difference of about 30 species, — the latter authority regard- 

 ing as species about 30 forms which I believe to be only varieties at the most. 



\ It is not, of course, assumed that we can ever attain a full and perfect ac- 

 quaintance with any ancient fauna or flora, but only so far as its remains have 

 been preserved, and so far as it may be possible to examine them. In this sense 

 our knowledge of one fauna may be full and complete, owing to more elaborate 

 researches, in comparison to what we know of another fauna which has not been 

 so well investigated. 



| It was supposed by Prof. King (Mon. Perm. Foss. p. xix) that his genus 

 Synocladia was confined to the Permian rocks ; but a Polyzoan occurs in the 

 Mountain Limestone of Settle, which undoubtedly belongs to the same group. 



