34 



MR. J. THOMSON ON THE OCCURRENCE OF DIPHYPHYLLTJM 



variable in strength and range, interstitial folates largely vesicular ; 

 terminal cup deep, lined by edges of the lamellae, no central boss." 

 Relative proportions of areas not constant. Diameter of corallites 4 

 to 4*5 lines. 



Localities. Carboniferous limestone, Kamensk, Siberian side of 

 the Oural, and Bristol, England. 



M'Coy found species of the genus and recognized the increase by 

 fission or fissiparity ; he published his definitions in Ann. & Mag. 

 Nat. Hist. ser. 2, vol. iii., and subsequently in his ' Palaeozoic Fossils 

 of Great Britain/ p. 88 (1855). Diphyphyllum latiseptatum and 

 D. gracile were there added to the English coral-fauna. 



M'Coy notices how rare dichotomous branching is amongst the 

 Cyathophyllidge, and that this form of increase distinguishes Diphy- 

 phyllum from Cyathophyllum. He states that there is no axis, and 

 that the corallites are biareal, the large central area being occupied 

 by a strong simple transverse diaphragm, deflected at the cir- 

 cumference, surrounded by a narrow, outer vesicular area. Outer 

 wall thick, radiating lamellae numerous, not reaching the centre. In 

 D. latiseptatum there are 28 primary septa and 28 smaller ones ; 

 D. gracile, which is a small form, has not one half the septal number 

 of the other species. There is no doubt that M'Coy thoroughly 

 understood Lonsdale's definition, and that his own specific diagnoses 

 are correct. 



Erom the time when M'Coy wrote, down to the present day, 

 nothing but doubt and denial have been associated with the genus so 

 well distinguished by Lonsdale. Milne-Edwards and Jules Haime 

 (Hist. Nat. des Corall. vol. iii. p. 434, 1860), considered Lonsdale's 

 species to be the same as M'Coy's D. latiseptatum, and that the genus 

 was founded upon specimens of Lithostrotion in which the axis had 

 been lost. They do not mention the fissiparous increase of the coral- 

 lites at all. Prof. Hall (Pal. New York, vol. ii. p. 113) describes 

 Diplophyllum and separates it from Diphyphyllum, recognizing the 

 affinities of the genera. 



Billings (Canadian Journ., March 1859) debated the fissiparous 

 method of increase in Lonsdale's genus, and yet separated it from 

 Lithostrotion on account of the defective axial structures. He, 

 moreover, considered Hall's genus to be synonymous with Lonsdale's, 

 which it is not. 



De Koninck gives an excellent history of the genus in his Eech. 

 sur les Anim. foss. du Terr. Carb. de la Belg. pt. 1, p. 33 (187 4). He 

 shows how Lonsdale separated the genus from Lithostrotion on account 

 of the absence of a columella, and criticizes Milne-Edwards and 

 Jules Haime. He does not, however, admit that fissiparity occurs, 

 and maintains that the appearance is due to the rapid coalescence of 

 young individuals which have been really produced by gemmation. 

 He agrees in this respect with M. Ludwig (Zur Pal. des Ourals, 

 p. 14, pi. ii. figs. 4, 5, 7). He Koninck, however, considers that 

 Milne-Edwards and Jules Haime have admitted the fissiparity, as did, 

 of course, M'Coy. He reflects upon the mistakes of D'Orbigny and 

 De Fromentel in using the generic name given by Lonsdale for very 



