ME. J. THOMSON ON THE GENUS DIPHYPHTLLUM. 



33 



5. On the Occurrence of Species of the Genus Diphyphyllum, 

 Lonsdale, in the Lower Carboniferous Strata of Scotland, 

 with a Description of some new Species and Notices of 

 Varieties. By James Thomson, Esq., E.G.S., &c (Read 

 March 24, 1886.) 



[Plates IT. & V.] 

 (Abridged.) 



The object of this communication is to offer evidence in favour of 

 the recognition of the genus Diphyphyllum, which was defined many 

 years since by Lonsdale, and which has not been definitely accepted 

 by any palaeontologist, with the exception of ALCoy. It is proposed 

 to give a slight history of the genus and species, and then to notify 

 the occurrence of all the species with varieties in somewhat remark- 

 able deposits in the Lower Carboniferous series of Scotland, and to 

 describe two new species and a variety of one of them. 



The facts now brought forward clearly prove the truth of 

 Lonsdale's diagnosis of the gonus, which enters the family Cyatho- 

 phyllidae of the Rugosa, and also necessitate the introduction into 

 the generic diagnosis of the words " increase by gemmation and by 

 fissiparity." 



The genus Diphyphyllum was defined by Lonsdale in Murchison, 

 Keyserling, and De Yerneuil's ' Geology of Russia and the Urals ' 

 (appendix, p. 622), and the type of the species D. concinnum, Lonsd., 

 is in the collection of the Geological Society of London. The defi- 

 nition was as follows : — " A stony lamelliferous polypidom ; lamellae 

 exceeding 12, biplated ; branched, branches dichotomous ; internal 

 structure, triareal — 1, central area intersected by flat, convex, or 

 irregular diaphragms, no persistent axis ; 2, intermediate area tra- 

 versed vertically by lamellae, interspaces crossed obliquely or down- 

 wards by extensions of the diaphragms and subordinate plates ; 3, 

 outer area traversed by lateral extensions of lamellae, interspaces 

 crossed by arched or vesicular laminae inclined upwards and outwards : 

 stems not uniformly thickened by external secretions, but occasionally 

 united when in juxtaposition." In explanation Lonsdale notices 

 that acicular points arise from the upper surface of the diaphragms 

 (tabulae), and sometimes are continuous through the diaphragms 

 above for a short distance, but there is no persistence of this struc- 

 ture so as to form a columella. The corallites are in ramified masses. 



Diphyphyllum concinnum, Lonsd., is defined as follows in the 

 above-mentioned work, p. 624, pi. A. fig. 4 : — " Stems cylindrical, 

 nearly smooth ; crossed externally by close, fine, waved lines, and 

 stronger, unequal, distant bands ; lamellae numerous, variable ; inner 

 surface of plates furrowed strongly upwards and outwards ; central 

 area, diaphragms flat, convex or irregular : intermediate area, prin- 

 cipal lamellae exceeding 30, more or less waved ; intermediate very 

 unequal : interstitial prolongations of diaphragms inclined sharply 

 downwards, accessory plates nearly horizontal ; outer area, lamellae 

 U. J. G. S. Iso. 169. n 



