ECHINODEEMATA. 31 



other fossils, and have been doubtfully referred to the modern 

 genera Discopora and Bcrenicea ; others, with slender branches, 

 and erect or creeping, are called Milleporas, Heteroporas, and 

 Escharinas. The genus Camites (fig. 3, 7), perhaps belongs 

 here. The magnesian limestone contains several large " lace- 

 corals" of the genera Fenestrella, Synocladia, and Phyllophora ; 

 and two branching species of Tliamniscus and Acanthocladia . 

 The oolites afford many small incrusting species related to 

 Biastopora, and branching forms like Terebellaria and 

 Chrysaora. In the chalk, the Escharas are most numerous, 

 and Lunulites and Capidaria first appear. Some thin beds 

 of the lower chalk are almost composed of Bryozoa, mingled 

 with Foraminifera. The coraline crag of Suffolk takes its 

 name from the great abundance of Bryozoa it contains, among 

 which Escliaro,, Cellepora, Fascicularia, Theonoa, Homera, 

 Idmonea, Flustra, and Tubuliptora are the most important. 



Class IV.— ECHIXODERMATA. 



(Star-Fishes, Sea- Urchins.) 



Char. — Marine ; commonly free, repent animals, with the 

 integument in most perforated by erectile tubular ten- 

 tacles, hardened by a reticulate deposit of calcareous 

 salts, and in many armed with spines. 



The fossil Radiata present a mine of comparatively unex- 

 hausted riches to the palaeontologist. More difficult of study 

 than shells, and less uniformly present in all strata, the 

 enduring remains of echinoderms and corals are unsurpassed 

 in beauty of form and structure, and in the value of the evi- 

 dence they afford. 



The present summary of the extinct forms of Echinoder- 

 ■mata will commence with 



