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



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

 Schweigger. (2) He accepted the genera StyJastrcea and 

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

 phylhim (subsequently changing its name to Nematophyllum) 

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

 and which are clearly astrseiforra species of Lithostrotion. 

 (4) He proposed the name of Stylaxis 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 

 Lithostrotion. 



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

 and Lasmocyathus for forms subsequently referred by Edwards 

 and Haime to Lithostrotion. 



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

 p. Ixxi.) accepted the genera Nematophyllum^ M'Coy, andZtV^o- 

 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 Stylaxis, M'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 

 Nematophyllian, 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 Avith regard to the affinities of this group of 

 corals. 



In 1852, Milne-Edwards and Haime still further expanded 

 their definition of Lithostrotion, 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 

 Stylaxis M' Coyana and >S'. Portlocki', 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, Avhich 

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

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

 vol. iv. p. "133). 



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



