Prof. W. King on Spirifer cuspidatus. 11 



settled, there can be no doubt that the phenomenon sought to 

 be explained is the result of metamorphism ; and I hold this 

 to be completely proved by the fact that in metamorphosed 

 examples of the tests of other Palliobranchs the perforations 

 disappear just as they do in Spirifer cuspidatus. Of va- 

 rious shells which I have examined, such as Dielasma {Te- 

 rebratula) hastata^ Pygope dipliya^ &c., I may confine myself to 

 Sjpiriferina laminosa^^ M^Coy, which has afforded me the clearest 

 evidence in favour of the above conclusion. The latter species 

 occurs in various conditions of fossilization : some of my spe- 

 cimens have the test well preserved, others have it completely 

 destroyed, and many have it in an intermediate condition. 

 The best-preserved specimens (for which I am indebted to 

 Mr. G. Tate, F.G.S., of Alnwick) that have passed under my 

 examination are from Redesdale, in Northumberland. The 

 fibres are well displayed, twisting about more or less, and 

 separating or pushed aside by the intrusion of the perforations. 

 In general the perforations are well defined, so that their dia- 

 meter, which is y^ inch, can be tolerably well determined. 

 They occur pretty regularly at about -2-0-0 iiich from one an- 

 other; but occasionally a smaller perforation makes its ap- 

 pearance in the intermediate spaces : their contents consist of 

 translucent granules, a dark-coloured matter, or a dusky- white 

 substance. Under a magnifying-power of 120 diameters, the 

 dark-coloured matter resolves itself into a congeries of crys- 

 tals of pyrites. Here and there a section appears without any 

 perforations ; or some present themselves more or less obscurely, 

 either as ill-defined aggregations of granules or indefinite 

 dusky spots ; the former are occasionally somewhat enlarged. 

 From the less clear appearance of the fibres in such places, 

 the absence or the obscurity of the perforations is evidently 

 due to a change in the shell-tissue. It is noteworthy that the 

 fibres, where mere traces of the perforations occur, occasionally 

 display only faint or uncertain indications of their deflection ; 

 rather they appear to continue straight on in their course. 

 Specimens which I have examined from other localities differ 

 remarkably from those collected at Kedesdale. Mr. W. H. 

 Baily, Palaeontologist to the Irish Geological Survey, has 

 favoured me with some from Hook Point and Tipperary ; but 

 they are all so completely silicified that nothing more than the 

 fibrous structure is retained. I have also succeeded in obtain- 



* Mr. Davidson and others have placed this species in Spirifer ; hut it 

 imdouhtedly helongs to Spiriferina. All the localities from which I have 

 examined specimens have yielded me dorsal valves of it vv^ith the medio- 

 longitudinal plate characteristic of the latter genus. 



