322 On a remarkable Species of the Genus Lithostrotion. 



In 1836 Prof. Phillips, in his 'Geology of Yorkshire' 

 (vol. ii. p. 2), noticed several species of corals. Gyatho- 

 phyllum hasaltiforme^ which M. -Edwards and J. Hairae 

 subsequently relegated to the genus Lithostrotion y and the 

 fasciculate species are referred to the genus Lithodendron. 



Mr. Lonsdale in 1845 applied the name of Lithostrotion to 

 four species ; a reference to his figures and descriptions leaves 

 no doubt that they belong to the genus Lonsdalia^ M'Goy. 



In 1849 M'Coy (Ann. & Mag. Nat. Hist. ser. 2, vol. ii.) 

 described various corals and created several genera for their 

 reception, but which cannot be separated from Lithostrotion. 



In 1852 M.-Edwards and J. Haime still further expanded 

 their definition of Lithostrotion ^ to which they then referred 

 the genus Stylaxis, M'Coy (Brit. Foss. Corals, p. 191), and at 

 the same time founded the genus Petalaxis for the corals 

 which they had formerly described under the names of Sty- 

 laxis M^ Coyanum and S. Portlockii. 



In 1861 De Fromentel (' Polypiers Fossiles ') restricted 

 the name of Lithostrotion to those species of the genus which 

 have an astraeiform corallum, whilst he placed the fasciculate 

 varieties under the genus Diphy phyllum, and further sepa- 

 rated some of the astraeiform species of Lithostrotion ^ together 

 with the two species of Petalaxisj Edwards and Haime, and 

 placed them under the revived genus Stylaxis, M'Coy, upon 

 the mistaken ground that the septa are not continued into the 

 external vesicular area, a condition which I have elsewhere 

 suggested was probably due to the endemic tendency to 

 variation *. 



In 1872 Prof, de Koninck (Anim. Foss. Nouv. Eech. 

 p. 26) defined the genus Lithostrotion in all the external 

 points as done by Edwards and Haime. He correctly shows, 

 however, that Diphyphyllum^ Lonsdale, is to be separated 

 from Lithostrotion. 



The great diversity of generic names that have been 

 applied to this group of corals, in which specific distinction is 

 even sometimes diflScult to define, is highly suggestive, 

 inducing us to realize that the genus includes a series of 

 varieties of an extremely varied character. Many of them 

 are so dissimilar in their external aspects, and in their struc- 

 tural details approach so closely their nearest allies, that it 

 becomes difficult to define the boundary of specific distinction. 

 Some of the structural characters upon which specific identity 

 has been accepted for several of the species are represented 

 in difierent corallites in this little group at present under con- 



* ' Transactions Phil, Soc, of Glasgow,' 1883, p. 404. 



