ANNIVERSARY ADDRESS OE THE PRESIDENT. 



99 



trace whence came for the first time the 17 genera of Hydrozoa, the 

 17 genera of Crustacea, 5 Annelida, 3 genera of Brachiopoda, and 5 

 of other Hollusca, &c, all presenting a different facies, or an aspect 

 having little affinity with the previously existing fauna. The advent of 

 the 17 genera and 42 species of Hydrozoa and the 35 species of Crus- 

 tacea, all new forms and widely spread, has still to be explained. 

 The 13 species connecting the Upper Tremadoc with the Arenig 

 belong chiefly to the Crustacea and Brachiopoda, these two classes 

 yielding 13 out of the 16 species. The 6 Crustacea are Asaphus 

 affinis, M'Coy, A. Homfrayi, Salt., Cheintrus Frederici, Salt., Dionide 

 atra, Salt., Ogygia]scutatrix, Salt., and 0. Sdwynii, Salt.; and the 

 Brachiopoda, Lingula petcdon, Hicks, Lingidella Davisii, M'Coy, L. 

 lepis, Salt., Obolella plicata, Hicks, Orthis Carausii (Hicks), and 

 0. lenticidaris. With these are Theca simplex. Salt., Conidaria 

 Homfrayi, Salt., and Bellerophon midtistriatiis, Salt. 



The Table numbered VII. embraces or shows the numerical value 

 and stratigraphical distribution of the species through all the Lower 

 Cambrian divisions, or from the Longmynd and Harlech group to 

 the close of the Tremadoc, and also shows in the last column, headed 

 " Pass to Arenig," the number of species that pass to that forma- 

 tion, or the base of the Silurian as now recognized by many syste- 

 matists. It will be seen that 11 genera and 16 species (J J) pass 

 to the Arenig ; and this mode of expressing the connexion between 

 the lower and succeeding formations is carried through all the 

 Tables. Thus the right-hand column shows" the number of species 

 passing up to the succeeding formation, and the left-hand column 

 (in all the Tables but this) those that came from an older or lower 

 series. As this special Table, and also Table No. I., shows the 

 commencement of life in the lowest rocks of the British Islands, 

 there are no forms older than those expressed by the number 61 genera 

 and 182 species. Their ancestors we know not ; neither do we 

 know whence was derived the fauna given under the 11 classes. The 

 6 smaller Tables distinctly show the more immediate relation of the 

 several divisions of the Lower Cambrian rocks : nevertheless this 

 completer Table is of value, showing, as it does, the whole range 

 from the Longmynd rocks to the top of the Tremadoc. 



I have endeavoured in my analysis of this Table, as in all the 

 subsequent ones, to express in words the result of the figures, 

 without which the Tables would merely enumerate the facts of 

 occurrences of no value to the student of geology and paleontology ; 

 and although of necessity tautology must be frequent, yet the 

 explanation, it is believed, will be clear. Throughout the whole 

 of the Tables (and there is one for each epoch) the genera 

 and species are given in the simplest form — the upper figure 

 in each square (and under each formation) enumerating the num- 

 ber of genera in the respective horizons, and the lower figure 



demonstrating the number of species, thus : ^p ec ^ es • This at once 



gives the census both zoologically and stratigraphically ; i.e. there are 

 4 genera and 20 species in the given horizon or formation. In this 



