Mr, R. Etheridge on Carhonifei'ous Polyzoa. 31 



Genus Fenestella (Miller), Lonsdale, 1839. 



(Murcliison's Silurian System, p. 677 ; King, restricted, 

 Perm. Foss. England, 1850, p. 35.) 



Fenestella arctica^ Salter, var. scotica^ var. nov. 

 (Plate II. A. figs. 1 & 2.) 



Fenestella arctica, Salter, Belcher's Last of the Arctic Voyages, 1855, 

 vol. ii. p. 38o, t. 36. f. 8. 



Spec. char. " Portions of foliaceous plane fronds, which 

 must have measured several inches across. The branches are 

 thicker than broad, rounded on the non-poriferous face, 

 slightly but regularly zigzag, and fully a third of a line broad ; 

 they are regularly radiating and bifurcating over the general 

 surface ; in-egular, and some of them much thicker, below. 

 Fenestrules broad, oval, a line long, and fully twice the width 

 of the branches. They are very regular in size and shape, 

 those at the bifurcation of the branches being similar and 

 equal to the rest. Non-poriferous face very slightly striated, 

 appearing smooth to the eye ; pores ?" 



Obs. I have lately had an opportunity of examining some 

 examples of this species from the Arctic regions, collected by 

 Captain H. W. Feilden, R.A., naturalist to the late Arctic Ex- 

 pedition, which has enabled me to name certain examples of 

 a Fenestella from our Lower Limestone group which I had 

 placed on one side for investigation. The diagnosis given 

 within inverted commas comprises the characters assigned by 

 Mr. Salter to his species ; but when a description can be 

 drawn up from Captain Feilden's specimens the specific cha- 

 racters will have to be much augmented and better defined. 

 The essential characters of the species, however, as defined 

 by Salter, are the zigzag interstices, giving rise to hexagonal 

 fenestrules, and their extreme regularity and similar disposi- 

 tion. The variety has essentially all the characters of the 

 species [the Arctic form], but simply on a finer and smaller 

 scale ; the hexagonal fenestrules are much smaller, and per- 

 haps the interstices and dissepiments proportionally wider as 

 compared with the size of the former. These data are cer- 

 tainly not of specific value, but will serve well as varietal 

 characters. The fine striae of the non-poriferous face of the 

 Arctic form are not visible on the variety ; that surface of the 

 latter appeal's to be quite plain. 



Without doubt there is a close resemblance between F. 

 arctica, Salter, and F. {Retepora) prtsca, Goldfuss. However, 

 neither in the figure given by Dr. Goldfuss*, nor in that given 



* Petrefacta Qermaniae, vol. i. t. 36. f. 19. 



