THE CAREOXIFEEOTTS FENESTELLIDiE. 



187 



Fexestella haekixexsis, sp. nov. 



JSp. char. — Polyzoarium a flat, oval, or circular expansion, folia- 

 ceons in its early growth, having a stem and expanded root-base. 

 Interstices flat, broad, very slightly rounded, keeled, the sides often 

 showing a flap or fringe. Dissepiments irregularly placed, very 

 thin in early stage, gradually thickening, rarely more than one 

 third of the thickness of the interstice. Fenestrules elongated, 

 becoming oval with increased growth, four in the space of two lines 

 measured longitudinally, and six in the same space transversely. 

 Fores small, round, often twice their diameter apart, three in the 

 length of a fenestrule, four and sometimes five in the later and 

 larger growth. Keel a narrow round wavy line, having three 

 nodes in the length of a fenestrule. 



This species at first sight would seem to have a strong resem- 

 blance to Fenestella plebeia, which, however, is soon dispelled by 

 careful scrutiny ; for it will be found to possess scarcely a feature 

 in common. Its broad flat interstices at once distinguish it from 

 the round or more often angular stem of .P. plebeia ; while the greater 

 distance between the cell-pores, and the thread-like nature of the 

 keel, complete the distinction. Again, the growth of F. plebeia is 

 noticeable for its regularity and smoothness, while T. TiaXkinensis is 

 by comparison coarse and irregular. The root-base of F. plebeia is 

 secured in position by numerous rootlets ; while F. JiaT/cinensis has 

 a broad, expansive and adherent base, which is further strengthened 

 by the interstices which, in favourable positions, directly adhere to 

 the rock by a similar flat calcareous base. Its expansion was not only 

 much smaller in size than that of F. jplebeia, but the last details would 

 seem to indicate a species of dissimilar habits, by attaching itself 

 to rock-surfaces which the rootlets of F. plebeia would fail to enter. 

 The affinities of this new species are, on the other hand, clearly with 

 Fenestella poly porata, Phill., rather than with F. plebeia. It has 

 very much the appearance of being a diminutive variety of Fenes- 

 tella polyporata, especially on the obverse face. 



Locality. Fairly abundant in the Cement-stone Quarries near Pen 

 yr Wylfa, Halkin Mountain, North Wales. 



It will be noticed that I have described only five species of 

 Carboniferous Fenestellce. I by no means wish it to be understood 

 that I do not believe in the existence of species other than those I 

 have described. Of these F. plebeia, M'Coy, F. nodulosa, Phill., 

 F. polyporata, Phill., and F. membranacea, Phill., are really the 

 principal and prevailing forms, and will be found in more or less 

 abundance in association with other Polyzoa, from the Calciferous 

 Sandstones of Scotland to the topmost beds of the Mountain- 

 Limestone series of North "Wales and elsewhere. The only partial 

 exception to the rule is Fenestella membranacea, Phill., which is 

 either absent or not so abundant at certain points and localities. 

 Having proved the existence and association of these species at 

 various horizons in the Carboniferous series, I speak confidently as 

 to the fact that the leading species of the Carboniferous Fenestellce 

 are few in number, while the reputed species are made up from the 



