562 Revieivs — Nicholson's Tabulate Corals. 



microscopic method of investigation to elucidate the intimate struc- 

 ture of fossil corals ; and the results which he has obtained serve to 

 show in a striking manner the importance and necessity of micro- 

 scopic examination in determining the intimate structure of corals. 

 The great amount of material which the author has been collecting 

 for many years past from those localities in Britain, the Continent of 

 Europe and America, which have yielded most of the known fossil 

 Tabulate Corals, has enabled him to carry out the task of a critical 

 description of these forms with the great advantage of being able at 

 will to compare and collate the specimens in his own cabinet. 



Though this book treats of the Palaeozoic Tabulate Corals, the 

 author fully recognizes the necessity of abandoning this division as 

 a natural group, and distributing the various families and genera 

 included therein by Edwards and Haime amongst the other divisions 

 of the Actinozoa. The presence of Tabula? or horizontal diaphragms, 

 which constituted the basis of the " Tabulata," has been shown by 

 the researches of Louis Agassiz on the animal of Millepora, ofVerrill 

 on Pocillopora, and Moseley on Millepora and Seliopora, to be of very 

 limited value as a main ground of classification, this structure 

 appearing alike in organisms which undoubtedly belong to the 

 Hydrozoa, Actinozoa, and Polyzoa. This fact of the existence of 

 tabula? in organisms so widely separated in the zoological scale has 

 given rise to great differences of opinion as to the true affinities of 

 the animals which constructed the numerous and varied tabulate 

 corals of the Palaeozoic rocks. Agassiz, basing his conclusions on the 

 Hydrozoal nature of Millepora, would have relegated all the 

 Tabulata to the Hydrozoa ; but Verrill showed from the true Zoan- 

 tharian character of the Tabulate Pocillopora that there was no 

 ground for such a sweeping conclusion, and this opinion has been 

 further justified by Moseley's discovery that the Tabulate Heliopora 

 belongs also to the Actinozoa. The absence of a satisfactory basis 

 for a determination of the true position of these fossils is sufficiently 

 manifested, however, by the very varied positions to which different 

 genera are assigned by the most eminent writers on this subject. 

 One has only to consult the memoirs on Eossil Corals by Professor 

 Martin Duncan, Dr. Lindstrom, M. Dollfus, Dr. Nicholson, Dr. 

 Eominger, Professor Zittel, and others, to be convinced of the diffi- 

 culty and uncertainty attending this subject. No small amount of 

 this division of opinion probably arises from an incomplete know- 

 ledge of these fossils, and therefore the new facts respecting their 

 minute structure which are recorded in the present treatise ought to 

 have a great influence in reconciling opposite views. 



Dr. Nicholson regards the old division of " Zoantharia Tabulata " 

 of Edwards and Haime as comprising twelve distinct groups of 

 animals, viz. Milleporidae, Pocilloporidae, Favositidae, Columnariada?, 

 Syringoporidae, Auloporidae, Halysitidas, Tetradiidae, Thecidae, Helio- 

 poridae, Chaetetidaa, and Labechidas. Of these, all, except the first 

 two families, are represented in the Palaeozoic period. 



The Milleporidae and Pocilloporidse being of comparatively recent 

 origin, do not enter into the scope of this work ; but the author fully 



