124 Herieivs — Prof. Dr. Nicholson — British Stromatoporoids. 



gation rests on the study of the minute structure of the skeleton, 

 and this can only be known by means of thin microscopic sections. 

 Of these, the author states that he has made considerably over a 

 thousand with his own hands, whilst most of the specimens were 

 collected by himself, from the Palaeozoic strata of this country, 

 North America, Germany, and Russia. By thus comparing the 

 microscopic characters of all, or nearly all, the known forms of the 

 group, under the different conditions of mineralization, it has been 

 possible to obtain a more complete knowledge of these organisms 

 than heretofore, and many features of importance, both as regards 

 the structure and relationship of the group, have been discovered. 



The first part of the Monograph contains the " General Introduc- 

 tion," which is treated under the following heads : (I.) Historical 

 Introduction. (II.) The General Structure of the Skeleton. (HI.) 

 Systematic Position and Affinities of the Stromatoporoids. (IV.) 

 Sketch Classification. (V.) Families and Genera of the Stromato- 

 poroids. (VI.) The Nature of Caunopora. 



(I.) Under the first head an account is given in chronological order 

 of the various memoirs on the group. From this we learn that the 

 type-specimen of Stromatopora concentrica, Goldf. (now preserved in 

 the Bonn Museum), which is the type species of the genus, exhibits 

 a structure greatly different from that which has generally been 

 regarded by palaeontologists as characteristic of the genus Stromato- 

 pora. The typical figured specimen of Goldfuss is a large mass of 

 numerous thick concentric strata (" latilaminae"), more or less undu- 

 lating, from 1*5 to 3 mm. in thickness, and separated by narrow 

 interspaces. Microscopic sections show that the skeleton is essen- 

 tially a complex net-work of anastomosing calcareous fibres, so 

 disposed as to inclose correspondingly complex anastomosing canals. 

 The minute characters of this typical form had not previously been 

 subjected to microscopical examination, and consequently the forms 

 assigned to the genus by Bargatzky, Carter, and others, which 

 possess structures of a different character, must necessarily be 

 included in a new genus, which the author proposes to name Acti- 

 nostroma, and which forms the type of the group Actinostromidai. 



(II.) Treating of the general structure of the skeleton of the 

 Stromatoporoids, the author states that the typical form is that of a 

 hemispherical mass or a flattened expansion, attached by a narrow 

 peduncle, or directly to some foreign body, but having the under 

 surface covered by a concentrically wrinkled imperforate epitheca, 

 while the apertures for the emission of the polypites are carried 

 upon the upper surface. Certain forms are ramose or dendroid, and 

 some habitually encrust other organisms. The skeleton was 

 originally of granular carbonate of lime, probably in the form of 

 arragonite, but this is now replaced occasionally by silica and by 

 crystalline calcite. One distinctive feature of the whole group of 

 the Stromatoporoids is the constitution of the skeleton of super- 

 imposed concentric layers. In some cases these are very thick, 

 strata-like, and made up of a series of vertical rods ('•' radial 

 pillars"), which run from the top to the bottom of the stratum, and 



