222 RUGOSA AND ALCYONARIA. 



In the Silurian Plasmopora, the corallum is very similar to 

 that of Heliolites, but the coenenchyma is more vesicular, 

 and its tubules are not so distinct. The g % enus Propora, 

 also Silurian, is very like the preceding, but the calices are 

 exsert. Lastly, we may mention the genus Polytremacis, 

 which hardly differs from Heliolites, save in its granular 

 surface, and which is remarkable in being found in rocks as 

 modern as the Cretaceous. 



LITERATURE. 



[In the subjoined list of some of the more important works treating of 

 the fossil corals, no distinction has been made as regards the different 

 orders, since most works of the kind quoted deal with members of two 

 or more of the orders.] 



1. " Manuel d'Actinologie et de Zoophytology." De Blainville. 



1834-37. 



2. " Klassen und Ordnungen des Thier-Reichs," vol. ii. ' Strahlen- 



thiere.' Bronn. 1859-60. 



3. " Histoire des Animaux sans Vertebres," vol. ii. Lamarck. (Ed. 2, 



1836.) 



4. " Histoire Naturelle des Coralliaires on Polypes proprement dits." 



Milne-Edwards. 1855-60. 



5. " Zoophytes." * Report of Exploring Expedition under Captain 



Wilkes.' Dana. 1848. 



6. " Polypiers Fossiles des Terrains Paleozoiques." Milne-Edwards 



and Haime. 



7. "Monograph of the British Fossil Corals." ' Palaeontographical 



Society.' Milne-Edwards and Haime. 



8. " British Fossil Corals." (Supplement to the preceding.) ' Palse- 



ontographical Society.' Martin Duncan. 



9. " Introduction a 1'etude des Polypiers Fossiles." Fromentel. 



1858-61. 



10. "Reports on the British Fossil Corals." < Rep. Brit. Assoc.,' 



1869-71. Martin Duncan. 



11. " On the Affinities of the Palaeozoic Tabulate Corals with Existing 



Species." ' Amer. Journ. Sci. and Art,' 1872. Verrill. 



12. " Affinities of the Anthozoa Tabulata." ' Ann. of Nat. Hist,' ser. 



4, vol. xviii. 1876. Lindstrom. 



13. " Monographic der Sclerodermata Rugosa aus der Silur-formation 



Estlands," &c. Dybowski. 1873. 



14. " Beitrage zur Kenntniss Fossiler Korallen." ' Deutsch. GeoL 



Ges.' 1870. Kunth. 



15. " Guynia and Haplophyllia." Phil. Trans.,' 1872. Martin Duncan. 



16. " Corals." ' Encyclopaedia Brit.' 9th ed., vol. vi. 1877. Nicholson. 



