On a new Species o/Diphyphyllnm. 317 



Hob. ? 



The nuclear whorls in tliis species are rather large in pro- 

 portion to the size of the shell. The longitudinal ribs are 

 but slightly developed, and at the first glance the surface 

 appears nearly smooth. 



XXXIX. — On a new Species of Diphyphylluin, and on a 

 remarkable Form of the Genus Lithostrotion. By James 

 Thomson, F.G.S. 



The object of the present communication is to describe a new 

 species of the genus Diphyphyllum, Lonsdale, and a 

 remarkable form of the genus Lithostrotion , Luidius. The 

 discovery of the former is due to His Grace the Duke of 

 Argyll, whose attention was directed to a remarkable 

 boulder that was exhumed by a farmer while digging a drain 

 in the boulder-drift on the farm of Carskey, near the south 

 end of Kintyre, Argyllshire. Notably, amongst other 

 erratics, there are numerous fragments and boulders of 

 granite, traceable to the island of Arran, situated to the east. 

 This boulder, so unlike the others, when more carefully ex- 

 amined, was found to be a mass of Carboniferous coralline 

 limestone. This species of Diphyphyllum * was noticed in 

 my paper on that genus published in the ' Quarterly Journal 

 of the Geological Society,' February 1887 ; it was not, 

 however, included for reasons that will be noted further on. 



The species of Lithostrotion I discovered at Blackridge, 

 Dumfriesshire, since the publication of my paper on that 

 genus (' Transactions of the Edinburgh Geological Society,' 

 February 1887). _ 



The genus Diphyphyllum was defined by Lonsdale in 

 Murchison, Keyserling and de Verneuil's 'Geology of Russia 

 and the Urals ' (Appendix, p. 622) . Lonsdale's definition 

 was fully reviewed in the above-mentioned communication, 

 and therefore need not be recapitulated. Briefly, he rests 

 his definition of the genus principally upon the mode of 

 reproduction, i. e. fissiparity, and the dichotomous branches. 

 In the present species the mode of reproduction is by calicular 

 gemmation, and the corallites are in dense masses and united 

 — characters unlike those of any of the then-known species of 

 the genus ; consequently its publication was deferred, and the 



* To His Grace I oifer my thanks for permitting me to add it to tlie 

 list of Carboniferous corals. 



