Vol. 51.] anniversary address or the president. Ixxxvii 



from various shapes of the bivalved carapace, with its peculiar hood 

 and autero-ventral notch (for the free movement of the antennae), 

 more or less expressed, we have Cypridinads in the Lower (and 

 Upper '?) Silurian, Devonian, especially in the Carboniferous (very 

 many in the Mountain Limestone and several in the Coal Measures), 

 and rare in the Permian. Cypridince occur also in Cretaceous and 

 Tertiary formations. 



' Why some ostracoda of somewhat specialized structure such as 

 Leperditia should have come into existence in the Upper Silurian, 

 and continued in nearly the same form for a few millenniums only, 

 while others like Cypridina, also of good standing, should have 

 begun even earlier, and lasted on, with diverse modifications, through 

 many more millenniums, is difficult to explain, except on the hypo- 

 thesis that the latter genus was enabled to have more variations and 

 adaptations to fit it for changing conditions of the sea. In this case it 

 could not have been so highly specialized as its earlier cousin-german, 

 nor does it seem to have yet given up its more generalized structure 

 for the specialized advancement which precludes more marked and 

 fundamental changes.' 



I have endeavoured to depict on p. lxxi. the evolution of the 

 arthropoda in geological time, and also, by means of diagrams, to 

 illustrate some of the leading forms of which I have spoken. 



In concluding this brief excursion over the abysses of Palaeozoic 

 time, I have only been able to bring under your notice a few isolated 

 points of interest in the crustacean fauna which lies in the depths 

 of these ancient deposits. They may, however, serve to show that 

 this group of lowly existences is not destitute of interest for the 

 biologist. There may also be a possibility of connecting these 

 isolated observations so as to show their bearing upon the greater 

 question of the development of life. 



In order, however, to do this effectively I must ask you to accom- 

 pany me next year in a second excursion over the newer Palaeozoic 

 and Kainozoic seas, where, nearer land and in shallower waters, we 

 shall find a still greater variety of life-forms to study. 



Two conclusions may be drawn from our observations, namely, 

 (1) that the ancient faunas of the earth were far more widespread, 

 more simple and more uniform than are our recent faunas ; and (2) 

 if, as the researches of geologists seem to indicate, other sedimentary 

 rocks exist, older than the Lower Cambrian, then we may hope to 



