84 Reviews, — Nicholson and Lydehher' 's Paleontology. 



the Invertebrata. We can within the limits of this notice only 

 refer to some of the changes and additions which appear in this 

 new edition. In Foraminifera, for instance, there is introduced the 

 new arrangement into families proposed by Dr. H. B. Brady, in the 

 "Challenger" Report, in which the structure of the test as an 

 exclusive hasis of classification has been abandoned. Figures are 

 given of some of the peculiar forms of the recent Astrorhizidae, in 

 which the test consists of arenaceous tubes, and to these the peculiar 

 genus Girvanella, lately shown to occur in many limestones from 

 the Cambrian to the Jurassic, is thought to be allied. The group of 

 the Dactyloporidaa, formerly included with the Foraminifera, now 

 finds its place with the Algae. In an Appendix, several pages are 

 devoted to a consideration of the structure of Eozoon, which the 

 author has investigated for himself, and some excellent woodcuts, 

 drawn from the author's own sections, convey a very good idea of 

 the microscopic appearance of this peculiar substance. Professor 

 Nicholson by no means rejects as inadmissible the idea of its organic 

 origin, but thinks that " until mineralogists or penologists are able 

 to point, in some unquestionable mineral or rock, to a structure 

 strictly comparable with the ' canal system ' of Eozoon, they are 

 not entitled to assert positively that the latter has a purely inorganic 

 origin." But a similar argument is applicable to those who assert 

 its organic origin, although no organism is known with a canal 

 system strictly comparable to this alleged structure in this rock. It 

 is to be hoped that the active investigation now in progress as to 

 the origin of the rocks in which Eozoon occurs, may help to decisively 

 solve the problem as to its real character. 



In the chapter on Eadiolaria, an outline is given of Haeckel's new 

 classification, and mention made of the presence of these organisms 

 in Jurassic strata where they form beds of jaspery chert. As the 

 microscopic structure of the siliceous organic rocks is better known, 

 this group will most likely appear more important as a rock-former 

 than has hitherto been supposed. 



The Sponges, which in the last edition were included under 

 Protozoa, are now placed in a separate sub-kingdom — the Porifera — 

 intermediate between Protozoa and Ccelenterata. They are divided 

 into two classes : the Plethospongiae, embracing the siliceous and 

 horny forms, as well as those without any hard skeleton, and the 

 Calcispongiaa. Our knowledge of the organization and distribution 

 of the fossil Sponges has greatly extended within the last decade ; 

 but owing to the liability of their skeletons to break up, we are 

 still ignorant of the complete forms of many of the older types, 

 and these can at present only be determined by their scattered 

 spicules, which are numerous enough to form considerable thick- 

 nesses of rock, more particularly in the Carboniferous epoch. The 

 family of the Beceptaculitidaa is, on Hinde's determination, included 

 with the siliceous sponges ; but Dr. Eauff, as mentioned in the 

 Appendix, questions the correctness of this reference, though he is 

 unable to refer this puzzling group to any other division of the 

 Animal Kingdom. 



