294 Mr. J. Thomson and Dr. H. A. Nicholson on the 



tion of Lonsdale [ = LonsdaJeia) to the genus Stromhodes, 

 Schweigger. (2) He accepted the genera StyJastrcea and 

 Diphyphyllum of Lonsdale. (3) He founded the genus Nema- 

 phylluni (subsequently changing its name to NematopliyUum) 

 for a group of corals of which N. arachnoideam is the type, 

 and which are clearly astrajiform species of Lithostrotion. 

 (4) He proposed the name of Styla.ris for corals which are 

 stated to differ from the preceding by their supposed fissiparous 

 development, and which are also clearly referable to Litho- 

 strotion as now understood. (-5) He proposed the name of 

 Siphonodendron for the corals referred by Phillips to Litho- 

 dendron^ which are now regarded as fasciculate species of 

 Liithostrotion. 



In 1850, M. D'Orbigny founded the genera Acrocyathus 

 and Lasmocyathus for forms subsequently referred by Edwards 

 and Haime to Lithostrotion. 



In 1850, Milne-Edwards and Haime (Brit. Foss. Cor. Intr. 

 p. Ixxi.) accepted the genera NematophyUum^ M'Coy, and Lifho- 

 dendron, Phill., separating the two principally by the alleged 

 presence of a well-developed accessory wall in the former, and 

 rejecting Stylaxis, M'Coy. They further applied the name of 

 Lithostrotion to the corals which we now term Lonsdaleia. 

 In 1851 (Pol. Foss. des Terr. Pal.) the same authors ac- 

 cepted the genus Stylaxi's, l^I^Coy ; they defined the genus 

 Lonsdaleia as at present accepted ; and they extended to the 

 genus Lithostrotion nearly its modern signification, placing 

 under it Lithodendron, Phill., Siphonodendron^ M'Coy, and 

 Nematophylhon , M' Coy . 



In 1851, Prof. M^Coy published his great work (Brit. Pal. 

 Foss.), in which he adhered to the views which he had pre- 

 viously expressed with regard to the affinities of this group of 

 corals. 



In 1852, Milne-Edwards and Haime still further expanded 

 their definition of Ltthosti-otion, to which they now referred 

 the genus Stylaxis, M'Coy (Brit. Foss. Cor. p. 191). At the 

 same time, they founded the genus Petalaxis for the corals 

 which they had previously described under the names of 

 Sty lax is M' Coy ana and S. Portlockt] and they further rejected 

 the genera Stylastrcea and Diphyphyllum of Lonsdale. 



In 1859, Mr. Billings gave reasons for retaining the genus 

 Diphyphyllum^ Lonsd., showing that it is properly separable 

 from Lithostrotion^ and that the absence of the columella, w^hich 

 forms one of its distinguishing characters, is not accidental, as 

 believed by Milne-Edwards and Haime (Can. Journ. new ser. 

 vol. iv. p. 133). 



In 1861, De Fromcntel (' Polypiers Fossiles ') restricted the 



