Yol. 5 I.J ANNIVERSARY ADDRESS OF THE PRESIDENT. lxxXV 



of the recent Nebalia. Caryocaris of the Arenig series possibly 

 belongs to the same group ; and the Upper Silurian Geratiocaris 

 carries the form to a high degree of perfection ; but until we meet 

 with the Nebalia of to-day we have no tangible links in this series 

 in intermediate geological times. 



So also one of the oldest forms, Waleott's Cambrian Protocaris, 

 is quite susceptible of being regarded as a predecessor of the living 

 Apus. The Carboniferous Dithyrocaris and its allies stand pro- 

 bably in the relation of genealogical links. 



But much more research among these interesting lower crustacean 

 fossils is required before their phylogenetic relationship can be fully 

 elucidated. 



The Ostracoda, which have the entire body enclosed in a shell or 

 carapace composed of two valves united along the back by a mem- 

 brane (represented by such forms as Cypris, Cypridina, Oandona, 

 Beyricliia, Primitia, etc.), are chiefly dwellers in shallows, and occur 

 both in fresh and salt water ; they are usually of minute size ; but 

 there are deep-sea types which attain comparatively large dimensions 

 (an inch long). They are met with in rocks of almost all ages from 

 the Cambrian upwards. To speak of them here is to recall the 

 nearly lifelong labours (from about 1840) devoted to their elucidation 

 by Prof. T. Rupert Jones, who has described many hundreds of 

 these primitive Crustacea from rocks of every British formation as 

 well as from very many foreign countries. 



Great as are the transformations which these organisms have 

 witnessed in the long cycles of geological change from Lower Cam- 

 brian to modern time, they present, nevertheless, a general facies, 

 and (like the genus Lingula amongst the brachiopoda) must be 

 looked upon as one of those persistent types which possess enormous 

 power of multiplication, so that entire beds of rock may be said to 

 be composed of their microscopic tests. The living species also 

 possess exceptional powers of endurance and provision for the 

 preservation of their lives in periods of drought, often retaining their 

 vitality in a dormant state perhaps for years ; thus they have persisted 

 tbrough all the vicissitudes of geological time, represented by the 

 entire succession of the stratified rocks : ' all things changing, but 

 themselves unchanged.' 



Prof. T. Rupert Jones writes : — ' Among the Palaeozoic ostracoda, 

 the simply smooth and oblong bivalved carapaces of the early Apar- 

 chites lead to more or less Leperditioid forms, some with slight 



vol. li. g 



