Reports and Proceedings — Royal Mioroscopical Society. 377 



Several giant species of NummuUna occur in early Tertiary times. 



II. PoRiFERA (the Sponges). — The Lithistid and Hexactinellid 

 Sponges have existed since Cambrian times. The Calcispongia^ 

 appear in late Palaeozoic times, and only become important in the 

 Mesozoic period. 



III. CcELENTERATA : (1) Hydrozoa.— The Graptolites are. world- 

 wide in their distribution ia early Palaeozoic time ; they are 

 enormously abundant and varied, and disappear at the end of the 

 Silurian period. Dicti/onemn, a doubtful Graptolite, extends from 

 the Cambrian to the Devonian. 



(2) Anthozoa. — Of the Corals the Eugose and Tabulate corals are 

 confined to the Palaeozoic rocks. 



The Hexacoralla are first seen in the Trias and continue to the 

 present day. Zaplirentis, Petraia, Glisiophyllum, and Strephodes, 

 all simple types of Eugose corals, range from the Silurian to the 

 Carboniferous age. The same range is found for Ci/athophyllum 

 and Diphypliyllum, both of which are compound forms. Of the 

 Hexacoralla four genera range from Jurassic to Eecent. 



Of the Tabulate corals (among the Eugosa) Favosites and Syringe- 

 pora range from Silurian to Carboniferous times. 



The existing corals belong to the Madreporaria, the Fungida, and 

 Perforata, and have no Palasozoic representatives, but the Secondary 

 and Tertiary deposits have yielded a large number of these forms. 

 The composite Madrepora include a vast number of forms, and range 

 from the Eocene to the present day. 



IV. BoHiNODERMA. — Of the Echinoderma the extinct groups, the 

 Cystoids and Blastoids, only lived in the Palaeozoic period. Of 

 Cystoids 50 genera and 250 species are known, and of Blastoids 

 19 genera and 120 species are recorded. 



The Crinoids appear to have declined ever since their maximum 

 development in Palaeozoic times. Ichthyocrhms ranges from the 

 Ordovician to the Carboniferous. Taxocrinus has the same range. 

 Of later forms Pentacrinus, Extracrinns, and Antedon have persisted 

 from the beginning of the Mesozoic period with very little change. 



Starfishes range from the Cambrian to the present day. 



Echinoids : regular forms like Cidaris have existed since the Trias. 



EcJiinocorys and some other irregular forms appear in the Cre- 

 taceous, but many of the genera quickly became extinct. But both 

 regular and irregular forms have continued on to the present time. 



V. PoLTzoA ('Sea-Mats'). — The Polyzoa date back to the 

 Ordovician. Of the Cyclostomata, Stromatopora and Berenicea 

 range through the whole time to Ordovician. Many living genera 

 range back into Mesozoic times. 



The Monticuliporoids, a peculiar group, perhaps related to the 

 Polyzoa, were dominant in Ordovician and Silurian times, but 

 doubtfully survived the Palaeozoic period. 



Of the Cryptostomata such genera as Fenestella, Polijpora, Bhabdo- 

 mesoii, and their allies are Palaeozoic. 



The Chilostomata, forming the bulk of living Polyzoa, date back 

 to the Jurassic period. 



