new Species o/'Dipliypliyllum. 319 



The corallum is in dense masses, prismatic from mutual 

 pressure, and closely aggregated, witli corallites of various sizes. 

 Diameter of corallites from 3 to 5 millim. (fig. 1, A). Epitheca 

 delicate ; the calice is moderately deep, and the floor is occupied 

 by broad flat tabulffi. The septa are of two orders, and their 

 inner ends rest upon the superior face of the tabulas. In a coral- 

 lite 5 millim. in diameter there are thirteen primary septa, 

 converging inwards for 1^ millim., and these alternate with an 

 equal number of secondary septa, which extend inwards fully 

 half the length of the primary, and they are united by endo- 

 thecal dissepiments. The septa are bilaminate, and there are 

 minute interlamellar plates (" stereoplasm ") inclining inwards 

 and downwards. A fossula is indicated. In the longitudinal 

 section (fig. 1, B) the tabula) are numerous and broad ; they 

 occupy two thirds of the total diameter of the corallum, and 

 are sometimes bent upwards in the centre, as in those species 

 in which development is by fissiparity. Vesicular structure 

 is present near the wall, in the interseptal loculi. Acicular 

 plates are rare. 



Locality. Found at Carskey, south end of Kintyre, Argyll- 

 shire, in boulder-drift, associated with boulders of Arran 

 granite. 



As regards the affinities of the genus Diphyphyllum as 

 defined by Lonsdale, it presents characters of a distinct 

 and fundamental nature, and is surrounded by genera 

 which possess structural details and external resemblances 

 which are combined and represented in it. In the type, D. 

 co?icinnuni, Lonsd., there is no columella : there are, however, 

 occasional acicular plates, which here and there bisect the 

 tabulae. If such corallites were sectioned transversely, 

 the plane of those acicular points would induce such to be 

 regarded as belonging to the genus Lithostrotion^ Luid., and 

 in this resppct this species indicates a transitionary tendency and 

 near relationship to the latter genus. There is another inter- 

 esting character in D. ArgyUii. In all the other species of the 

 genus the septa extend inwards from the wall more or less into 

 the centre ot the corallum ; there is, however, in some of the 

 corallites of D. ArgyUii a departure from that condition, as 

 the septa are interrupted by vesicular tissue, and therefore do 

 not reach the wall, in this respect indicating a transitional ten- 

 dency in an opposite direction, and towards the genus Tliy- 

 sanophyUum, 'I'honis. & Nich. (fig. 2)-: in the latter the septa 

 are intercepted and never reach the wall ; in other respects the 

 structural details are similar to those of the genus Dii)hy- 

 phyllum. The question presents itself. How are we to con- 

 sider these modifications? — whether they are of sutficient 



