124 Mr. J, Thomson and Dr. H. A. Nicholson on the 



Foss. des Terr. PaL p. 446). On the contrary, there is abun- 

 dant evidence that no columella ever existed in any of the 

 corals properly referred to Dijjhyphyllum. 



Tlie septa are well developed; but the primary ones invariably 

 fall short of the centre, and leave the tabulae exposed over a 

 larger or smaller median space. Towards the circumference 

 of the visceral chamber the interseptal loculi become filled by 

 minute lenticular vesicles, formed by the development of nume- 

 rous dissepiments (PI. VIII. fig. 1). 



The epitheca is thin, with encircling stria;, and occasionally 

 accretions of growth. Sometimes there are horizontal out- 

 growths of the epitheca, uniting two adjacent corallites ; but 

 this is of rare occurrence. 



Mr. Lonsdale's original definition of the genus Diiiliy^jliyUum 

 is as follows {op. jam cit. p. 623, t. i.) : — "A stony lamel- 

 liferous polypidom ; lamella exceeding twelve, biplated ; 

 branched, branches dichotomous ; internal structure triareal : 

 (1) central area, intersected by flat, convex, or irregular dia- 

 phragms, no persistent axis ; (2) intermediate area, traversed 

 vertically by lamellas ; interspaces crossed obliquely or down- 

 wards by extensions of the diaphragms and subordinate plates ; 

 (3) outer area, traversed by lateral extensions of lamellae ; inter- 

 spaces crossed by arched or vesicular laminae inclined upwards 

 and outwards; stems not uniformly thickened by external secre- 

 tions, but occasionally united when in juxtaposition." The 

 type species, upon which the above definition is founded, is 

 D. concinnum^ Lonsd., from the Carboniferous rocks of 

 Russia. 



Prof. M^Coy (Brit. Pal. Foss. p. 87) followed Mr. Lonsdale 

 in all essential points, more es])ecially as regards the supposed 

 fissiparous mode of increase, and defined the gfenus as follows : — 

 " Corallum forming elongate cylindrical branches, dividing by 

 dichotomous fissure of the main stem ; no axis ; biareal ; the 

 large centi'al area occupied by strong, simple, transverse dia- 

 phragius, deflected at the circumference, surrounded by a naiTow 

 outer vesicular area ; outer wall thick, radiating lamellffi nume- 

 rous, not reaching the centre." He described two species, from 

 the Carboniferous rocks of Britain, viz. D. gracile and D. lati- 

 septatum^ the latter of these being apparently identical with 

 D. concinnum, Lonsd. 



Milne-Edwards and Haime consider that Dipliypliylluni 

 concinnum was founded upon a Lithostrotion in Avhicli the 

 columella had been accidentally destroyed, and they therefore 

 reject the genus altogether (Pol. Foss. des Terr. Pal. p. 446). 

 De Fromentcl adopts the same view, but retains the name of 

 DiphyjyhylUnn for the fasciculate species of Lithostrotion (Int. 



