Prof. W. King 07i Spirifer cuspidatus* 13 



" the fibres could be clearly seen on each side of a perforation 

 deflected slightly to one side in passing as it were around it." 



Reverting to Spiriferina laminosa^ it cannot now for a mo- 

 ment be questioned that the changes which its shell-tissue, in 

 the Irish specimens, have undergone are caused by metamor- 

 phism. Is it right, then, to reject the same agent in Spirifer 

 cuspidatus^ because in this species (I contend, on account of the 

 miusually small size of the perforations) the evidences of its 

 action in a certain stage cannot be absolutely accepted as de- 

 monstrated ? 



Impressed with the preceding evidences and considerations, 

 I can only conclude that, wherever imperforate spaces occur 

 in Spirifer cuspidatus^ perforations were originally present in 

 them. And although Mr. Davidson's specimen (also, it must 

 be remembered. Prof. Harkness's) may be noted as " exhibit- 

 ing not the smallest trace of perforations," I have no hesita- 

 tion whatever in adopting the same simple conclusion in this 

 case as well, rather than seek for its explanation in any strange 

 morphological doctrine. 



Apophysary System. 



It has long been known that various Spiriferids are fur- 

 nished with a pair of dental plates, differently modified accord- 

 ing to species ; but it is not so well known that many of them 

 have these parts united so as to form an apophysis more or 

 less resembling the arch-shaped chamber characteristic oiPen- 

 tamertiSj Stricklandiniaj and CamaropJioriaj though in many 

 species its exact homology with the latter appears very doubt- 

 ful. In a number of the cases to which reference is made, the 

 apophysis, as will shortly be seen, is so small, or so obscured 

 by a deposit of shelly matter between its outer surface and th^ 

 inside of the umbonal cavity, as to render its individuality 

 difficult to make out, causing it to appear, in the latter case, 

 like a depression excavated in the substance of the umbone. 



Professor Phillips appears to have been the first who de- 

 tected the process in the Spiriferids ; for in his description, 

 published in 1835, of Spirifer septosus^ this species is stated 

 to have " the septa in the lower valve dividing it into three 

 parts, as in Fentamerus^""^ . It is now well known, through 

 Davidson's careful labours and excellent figures, that the spe- 

 cies above named has the dental plates curving inwardly to- 

 wards each other, and then uniting, so as to form a complete 

 arch. The plates, which do not separate again, as in a num- 

 ber of Spirifers, remain united, producing a well developed 



* Geology of Yorkshire, vol. ii. p. 216. 



