ANCIENT SEDIMENTS. 321 



to the genus. And, also, there is no doubt that Professor 

 J. W. Dawson's Naiadites is older than Salter's Anthra- 

 coptera, although Dawson's genus originally contained mem- 

 bers of all the oenera to be described in this work." Further 

 information concerning the synonymy of the group may be 

 obtained by reference to a paper by the present author pub- 

 lished in the Quarterly Journal of the Geological Society, 

 which contains a list drawn up by E. T. Newton, also 

 in a paper by Professor Amalitsky in the Quarterly 

 Journal for 1895, and in the report of the discussion 

 thereon. With regard to the conditions under which 

 the group lived, it is well known that Salter, in opposi- 

 tion to nearly all other authorities, upheld its marine 

 character. The author presents and weighs all the avail- 

 able evidence bearing upon this question, and decides es- 

 sentially in favour of a freshwater habitat. He sums 

 up as follows : " On the whole very little positive evidence 

 can be brought forward on behalf of a marine habitat for 

 these shells, while there is, to say the least, a fair amount 

 of presumption that they lived under freshwater conditions. 

 It may be, however, that we have in the occurrence of Car- 

 bonicola and Naiadites with various marine forms at the 

 base only of the Coal- Measures an example of a genus 

 changing its habitat. It is probable that all molluscan 

 forms were originally marine in habit, and that by modi- 

 fication and adaptation some few forms became able to 

 exist in fresh water ; and it is also probable that this 

 adaptation took place at different times, and is even going 

 on now, to wit, the discover)' of Hydrobia Jenkiusi in in- 

 land canals of late years, which shell had till that time been 

 only known under estuarine conditions." The author's view 

 is thus substantially in accord with that previously expressed 

 by Prestwich, John Young, Green, and others. The present 

 contribution to this Monograph contains a description of the 

 British species of the genus Carbonicola (Anthracosia). 



BIBLIOGRAPHY. 



(1) SUESS, E. Beitrage zur Stratigraphie Central Asiens. Denk. 

 Mat. Natur. CI. K. Akad. Wissen. Wien, vol. Ixi., p. 431. 



