156 GEOLOGICAL DISTEIBUTION-. 



apparently, of this very numerous order having survived the Car- 

 boniferous period. Here, also, we have the almost final disappear- 

 ance of the two great groups of the rugose and tabulate corals, 

 which by their numbers so eminently characterise the limestone 

 deposits of the Paleozoic series, from the Silurian to its close. The 

 Permian flora is essentially that of the Carboniferous period, and 

 requires no special consideration. 



Paleozoic Faunas. — Briefly reviewing the more salient features 

 of the Paleozoic faunas, we find, as far as the invertebrate series is 

 concerned, that with few exceptions all of its recognised classes 

 have their representatives, or, at least, there are representatives of 

 nearly all those classes whose members could reasonably be expected 

 to have been preserved in a fossil state. Thus, of the Protozoa we 

 have the Foraminif era and Spongida ; of the Coelenterata, the Acti- 

 nozoa and Hydrozoa ; of the Echinodermata, the Echinoidea, Aste- 

 roidea, Ophiuroidea, Crinoidea, Cystidea, and Blastoidea ; of the 

 Mollusca (and MoUuscoida), the Polyzoa, Brachiopoda, Acephala, 

 Pteropoda, Gasteropoda, and Cephalopoda; and of the Articulata, 

 the Crustacea, Arachnida, Myriapoda, and Insecta. Of the classes 

 here enumeratedthere are wanting in the Cambrian the Actinozoa,* 

 and possibly also the Hydrozoa; the Echinoidea, Blastoidea, and 

 Ophiuroidea, among the echiuoderms ; and the Arachnida, Myria- 

 poda, and Insecta, among the articulates. In the Silurian the 

 number of missing classes is reduced by six, since we have here 

 representatives of both corals and hydroids, blastoids and brittle- 

 tars, insects and arachnids ; but the last two are represented almost 

 by single individuals. In the Devonian the number is further re- 

 duced by one, the class of the Myriapoda, likewise (as is also the 

 case with the insects) represented in almost solitary individuals; 

 only with the Carboniferous period do all the classes acquire for 

 the first time any marked development. We thus cannot fail 

 to remark the progressive evolution of new forms correlatively 

 with the advance of time. Of the vertebrate series the Paleozoic 

 deposits contain the remains of only three of the five recognised 

 classes, the fishes, amphibians, and reptiles, which appear serially 

 in the order of their progressive organisation, the lowest, or fishes, 

 in the Silurian (or, if the conodonts be fishes, in the Cambrian), the 

 amphibians in the Carboniferous, and the highest, or true reptiles, 



* Some forms have been doubtfully referred to this period in Scandinavia. 



