Correspondence— Dr. J. W. Gregory — Mr. F. R. C. Reed. 427 



" We have still to inquire into the causes which led to the Siberian 

 migration, and to ascertain the geological period during which it 

 took place. In order to arrive at a more satisfactory conclusion on 

 these problems, it is of some moment to study the extinct fauna of 

 Siberia." (p. 449.) 



" Since Tcherski has shown that Western Siberia is largely covered 

 by fresh-water deposits, the assumption that the Aralo-Caspian had 

 been in direct communication with the Arctic Ocean as recently aa 

 the Pliocene ejDOch can no longer be maintained ; but, as we shall 

 see presently, there is some evidence in favour of a European con- 

 nection between the two seas." (p. 453.) 



[To he continued in our next Number.) 



co:E^I^:ESI=035^3D IB liTGE. 



TRESPASSERS, BEWARE! 



Sir, — I am grateful to my '• kalikali " colleague, Mr. F. A. Bather, 

 for pointing out that (in common with the more learned palseon- 

 tologists who have recently prepared a Synopsis and a Eevision of 

 the Cystoidea) I had overlooked the fact of a new name having 

 been proposed for Hall's Echinoct/stis in the last edition of his 

 friend Mr. S. A. Miller's Catalogue. 



In regard to Discocystis, a defence of the name would involve 

 a greater trespass into the domain of the Cystoidea than I was 

 recently forced to make in relieving the term JEchinodiscus from 

 double duty in Echinoderra nomenclature. A review in the current 

 number of Natural Science helps me to resist the temptation ; for the 

 reviewer, whose information is apparently of the best, deplores 

 the brief treatment of the Cystoidea in the new Guide to the Fossil 

 Invertebrata in the British Museum, although " our National 

 Museum possesses not only a fine collection of those rarities, but an 

 officer well qualified to deal with them." J. W. Gregoky. 



TRINUCLEUS SETIGORNIS. 



Sir, — It is satisfactory and instructive to find in last month's 

 Geological Magazine Mr. Marr so clearly indicating his early 

 mistake about the range of Trinucleus seticornis, for he mentions 

 in his criticism of my remarks that in 1883 he had stated that 

 this species was nowhere found in the Upper Bala, while in 1885 

 he was led to call some Upper Bala beds in South Wales the 

 T. seticornis beds, on account of its abundance in them. After this 

 presumably conscious acknowledgment of an error, I am, therefore, 

 surprised to find Mr. Marr much troubled in mind because I naturally 

 considered that his statement of 1885 considerably qualified, or even 

 negatived, his earlier one of 1883. Perhaps Mr. Marr wishes to 

 make another correction in his opinions published in 1885. 



With regard to the identification of this protean species of tiilobite 

 I exceedingly regret that infallibility cannot be claimed as a pre- 

 rogative by eminent geologists, or even by " very competent palason- 

 tologists," at any time of their life, and that consequently Mr. Marr 



