226 VINE : PALAEONTOLOGY OF THE WENLOCK SHALES. 
Mr. Etheredge delivered his address, much of the old material has been 
re-worked, and many new species have been added to previous lists, 
but only a few classes have been persistently overalled by the 
palneontological student, notably the brachiopoda by the late Dr. David- 
son, and the polyzoa, annelida, and entomostraca, by myself, Prof. 
T. Rupert Jones and Dr. Holl; if then we are to compare favourably 
the list of Wenlock shale fossils, now given at the end of this paper, 
we must except the genera and classes which have neither been added 
to nor reduced in number. The excepted genera, and their included 
species^ belong to the classes hydrozoa, lamellibranchiata, heteropoda, 
and cephalopoda, and this will reduce the genera dealt with to 58, 
and the species to 110. Taking the Upper Silurian fauna generally, 
as given by Mr. Etheredge, we find that though there may be an 
absolute unconformity of the Upper Llandovey beds to the strata 
below "the changes of species in the two horizons may be due to 
causes of which we have no positive proof," yet, as Mr. Etheridge 
suggests, " looking at the intimate connexion between the fauna of 
the Lower Llandovery and that of the Upper, we are led to suppose 
that it was not of sufficiently long duration to cause either the ex- 
tinction or migration of the older fauna or the introduction of a 
new one (only 4 genera seem to have appeared) : for . . the Lower 
Llandovery transmitted 45 genera and 104 species out of its fauna 
of 68 genera and 204 species to the Upper Llandovery. It is there- 
fore evident that upheaval and denudation must have been of com- 
parative short duration, and little physical change could have taken 
place in the area occupied by the Lower Llandovery after upheaval: 
this the physical geography and paLoontology of the two groups 
help to show."''' Of the transmitted groups of fossils from the one 
horizon to the other, many of the species are as common to our own 
rocks as to the Upper Silurian rocks of Gotland,! yet I find that 
many genera and species common to the Gotland groups are very 
poorly represented in our own Wenlock shales. The causes of this 
may be manifold, but one chief reason for the paucity may be ac- 
* Op. cit, p. 125. 
f Dr. Lindetrom's list of Fossils, 18&5, is before me while I write, 
