126 ON PERMIAN ENTOMOSTRACA FROM 



Mesozoic element in tins section of the Permian fauna, it being 

 more properly a Mesozoic and Cainozoic form, although it is 

 first met with in Palaeozoic rocks. As a connecting link with 

 the older rocks, the generic form typified by Kirkhya Permiana 

 and its varieties, may be noticed, as the representative of its more 

 ancient prototypes the Beijricliia and Leperditia, of the early 

 Palfeozoic rocks. This form appears to predominate in Russia: 

 three varieties occur there; another is found in Germany, and 

 two in Durham. According to our present knowledge, only one 

 other species is known as belonging to this genus, namely, an 

 undescribed form from the lower Carboniferous rocks near Glas- 

 gow. Consequently, it is pre-eminently characteristic of the 

 upper Palaeozoic deposits. Associated with the Permian species 

 belonging to the above groups, are a few forms which have been 

 referred to Cythere, Cytlweis ?, and CythereUa ?, all of which, with 

 one exception, are found in the upper Permian limestone of 

 Byers' Quarry, and some of which also occur in the Unter Zech- 

 stein of Germany. At Byers' Quarry these forms are in the as- 

 cendant, being seven in a list of twelve species (or varieties) 

 found therein. Species belonging to these groups have also 

 been found in the shell-limestone. 



As I have already suggested, the differences observed in the 

 generic affinities of the species of Entomostraca found in the 

 shell-limestone and the limestone of Byers' Quarry may indi- 

 cate some differences in the physical conditions pertaining to the 

 area of deposition of each. And from considerations independent 

 of the evidence offered by these fossils, I am inclined to ascribe 

 it to a difference in depth of the sea or seas of deposition. In 

 regard to the limestone of Byers' Quarry, there seem to be 

 sound reasons for considering it to have originated in water of 

 no great depth — at least not beyond the range of Algce, for from 

 the beds of the same quarry I have taken numerous vegetable 

 remains, which undoubtedly belong to that class. There are 

 other facts which appear to support this opinion — which is no 

 new theory, being already broached by Professor King — but 

 which it is needless to detail at present. So far as the origin of 

 the shell -limestone is concerned, there seem to be as good rea- 



