ANNIVERSARY ADDRESS OF THE PRESIDENT. XXXVU 



in the ornaments in tlie test, striation mainly preceding granulation. 

 Features, however insignificant, of this kind chiefly give a distin- 

 guishing facies to the fauna of an epoch. Well was it said by Von 

 Buch, that "the smallest difference acquires value by constancy." 



I shall not attempt an analysis of the elaborate general zoological 

 division, of M. Barrande's work, or of the complete treatise on 

 Trilobitic species that follows it. Suffice to say, that no student 

 of Crustacea can be absolved from a close perusal of this most admi- 

 rable monograph, and that every Silurian geologist should endeavour 

 to understand and master its luxuriant details. In justice to the 

 author, there is one section of this part of his work that cannot be 

 passed without a remark, and that is, his chapter concerning the 

 metamorphoses and modes of existence of Trilobites. 



For years, ever since 1828, palseontologists have dreamt of Tri- 

 lobitic metamorphoses, and some have pronounced definitely for, 

 some as definitely against, the probability of the Trilobite under- 

 going changes in the course of its existence as an individual. The 

 full discovery and statement of the fact was reserved for Barrande in 

 1849. In the same year Mr. Salter showed that the young indivi- 

 duals of Ogygia Portlockii presented 4-7 segments, and finally 8. 

 Milne-Edwards and Burmeister, naturalists thoroughly versed in 

 the history of living Crustacea, had previously speculated freely 

 from analogy on the probability of their transformations. M. Bar- 

 rande in the work before us demonstrates a metamorphosis in no 

 fewer than 16 genera and 28 species. The degree of change is 

 variable ; its intensity comparable with the phsenomenon in existing 

 Crustacea. The successive and progressive elaboration of all the 

 elements in the pygidium before becoming free and passing into the 

 thorax, holds good in all known metamorphosing Trilobites. The 

 number of species in which a change has been proved diminishes as 

 v/e ascend in time. Among other points M. Barrande has made out 

 the probable eggs of these animals. As to their mode of life he 

 opposes the conclusion of Burmeister and others, that Trilobites 

 lived in shallow water along the coast ; and distinctly pronounces 

 against the supposition of their parasitic nature. 



The Geology of the British Isles. 



The well and often explored mine of British geology has not yet 

 been worked out, and there are still rich lodes to discover, as well as 

 old workings, that yield profitable returns when re-examined. Our 

 Journal has had its full and usual share of papers on British strata 

 during the past year, and, judging from what I know of memoirs in 

 hand, the coming sessions are likely to be quite as well provided for. 



Our Palaeozoic rocks have received their usual share of attention. 

 Old though they be, they are as attractive as ever, and their warmest 

 admirers during pi-ecediug years remain constant to their antiquated 

 yet ever fresh charms. The often discussed question of their 

 classification has been made the subject of a communication by Pro- 

 fessor Sedgwick to the Geological Section of the British Associa- 



