CCELENTERATA : ACTINOZOA. 1 39 



entirely Palaeozoic, with the single exception of the genus Holo- 

 eystis which is represented in the Secondary Rocks by a single 

 species (viz., H. elegans, from the lower Greensand) and- a few 

 Tertiary forms. In the lower Palaeozoic Rocks the Rugosa 

 are especially abundant ; but in the Permian formation the 

 order is represented by the single genus Polycxlia. 



The Zoantharia Sclerodermata, though attaining their maxi- 

 mum at the present day, nevertheless are well represented 

 in past time, beginning in the Silurian period. One subdi- 

 vision of this group, the Tubulosa, is entirely confined to the 

 Palsozoic Rocks, and another, the Tabulata, is chiefly Palseo- 

 zoic. The Perforata and Aporosa, on the other hand, are more 

 abundant in the Mesozoie and Kainozoic Epochs. 



The Zoantharia Sclerobasica are hardly known as fossils, but 

 the Miocene deposits of Piedmont (Middle Tertiary) have 

 yielded a species of Antipathes. 



The Zoantharia Malacodermata, from the soft nature of their 

 bodies, are obviously incapable of leaving any traces of their 

 existence ; though we are by no means therefore justified in 

 asserting that they did not exist in past geological epochs. 



The Alcyonaria are very doubtfully represented in rocks 

 older than the Chalk; the Lower Silurian fossil called Pro- 

 tovirgularia being more probably referable to the Hydrozoa. 

 One of the Pennaiulidce (viz., Graphularia) has been found in 

 the London Clay (Eocene), and the same formation has like- 

 wise yielded two species of Gorgonidm (Mopsea and Websteria). 

 The genus Corallium has likewise been found in deposits of 

 Miocene age. 



The Ctenophora, being entirely destitute of any hard structures, 

 are not known at all as occurring in the fossil condition. 



Appendix giving a Tabular View of the Divisions of the 



Zoantharia Sclerodermata and Rugosa (after 



Milne-Edwards and Jules Haime). 



A. The Zoantharia Sclerodermata are defined by the possession of a 

 Eclerodermic corallum, the parts of which are arranged in multiples of five 

 or six. Septa generally well developed, but not combined, as a rule, with 

 tabulse. 



The following chief divisions of the Zoantharia Sclerodermata are, with 

 few alterations, those adopted by the above-mentioned authorities : — 



I. Tabulata. — Septa rudimentary or absent; tabulie well developed, 

 dividing the visceral chamber into a series of stories. 



1. Thecidm. — Corallum massive ; a dense spurious coenenchyma formed 



by the lateral union of the septa ; tabulae numerous. 



2. Favositidie. — Septa and corallites distinct; little or no true ccenen- 



chyma. 



