chief Generic Tyjpes of Faloiozoic Corals. 125 



h, r^tude des Polyp. Foss. p. 304) . Prof, de Koninck, how- 

 ever, by his excellent description and figures of the type form, 

 D. concinnum, Lonsd., has thoroughly established the correct- 

 ness of Mr. Lonsdale's original views and the validity of the 

 genus (Nouv. liecherches sur les An. Foss., partie i. p. 36, 

 pi. ii. figs. 4-4 c?, 1872). We need only add that the forms 

 which we have examined from the Carboniferous rocks of 

 Scotland and the Devonian rocks of America agree in all points 

 of generic importance with the type form D. concinnwn. We 

 quite agree with Mr. Billings (Can. Joui-n., new series, vol. iv. 

 }). 134), as well as with M. de Koninck, in thinking that 

 Mr. Lonsdale was in error in making fissiparous division to 

 be one of the characters of the genus ; but this misconception 

 as to a single character is not of itself sufficient to invalidate 

 his definition or to lead to the abandonment of his name. 



It follows from the above that the genus LitJiostrotion is 

 sufficiently separated from Diphyphyllum by the presence in 

 the former of a well-developed and continuous columella, which 

 is wholly wanting in the latter. Hence transverse and longi- 

 tudinal sections will in all cases enable the palgeontologist to 

 at once separate the Diphi/phylla from the fasciculate species 

 of Lithostrotion^ in spite of the close external resemblance 

 between the two groups. 



From the typical species of Cyathophyllum the species of 

 Diphypliylluni are at once separated by the limitation of the 

 septa of the latter to the external portion of the corallum. In 

 no case do the septa in DiphyjpliyUum meet in the centre of the 

 visceral chamber, or become twisted together so as to form a 

 pseudo-columella. This distinction, however, is not available 

 as separating DipTiypliyUum from forms like Cyathop>]iyllum 

 paracidciy M'Coy, or C. [Caninia) giyanteum^ Mich., since in 

 these latter the septa fall short of the centre. In this case 

 the chief available characters are to be found in the fasciculate 

 growth of the former, and the strongly developed peripheral 

 vesicular zone of the latter. When we come, however, to such 

 forms as C. ccespitosum^ Goldf., it must be admitted that it is 

 almost impossible to draw a rigid line between this ani]. Diphy- 

 phyllum, since the septa in the former seem occasionally to 

 fall short of the centre, and the form and mode of growth of 

 the corallum are as in the latter genus. 



Dybowski has recently founded the genus Donacopihyllum 

 (Mon. der Zoanth. scler. rug. aus der Silurform. Esthlands &c., 

 p. 80) for corals which are said to differ from Diphyphyllum 

 only in the fact that the vesicles of the exterior zone are of 

 large size. We have seen no examples of the genus, and can 

 pronounce no opinion as to its value. 



