BRITISH UPPER SILURIAN FENESTELLTD^. 251 



fenestrules on the other — is so great that the error of making the 

 latter into a new species might be excused; it is an instructive 

 incident in the history of the Palaeozoic Polyzoa. Taken altogether, 

 we may claim for this species a premiership of beauty among 

 beautiful forms. 



Since writing the above I have ascertained that Hall mentions* a 

 species {Polypora incepta)^ from the beds of the Niagara group (the 

 Upper Silurian of North America), allied to the foregoing, only with 

 the PoZ?/pora-character still more developed by having the rows of 

 pores increasing from two to four instead of from two to three, as in 

 Fenestella intermedia. In this case he assigns, rightly, I believe, the 

 species to Polypora, on account of its having so many as four rows 

 of pores on the interstice. As to the question whether Fenestella 

 intermedia, with its three rows of pores, ought also to be included 

 with Polypora, it may fairly be left open for consideration. It is to 

 be borne in mind that the Po Zypora-features are not so strongly 

 marked in it as in the other case, and that the facies generally is 

 that of Fenestella ; to refer it to Polypora, therefore, would be to 

 ignore its leading character. It may be, and is, difficult in practice 

 to draw the line as to where Feiustella ends SiTidPolyjJora begins. The 

 genus Polypora was founded by Prof. M'Coy for that division of the 

 Fenestella family having more than two rows of cells on the 

 interstice ; the usual number of rows of cells in Polypora is from 

 three to ten. These intermediate or compound forms, as Polypora 

 incepta or Fenestella intermedia, were then unknown, and the 

 difficulty as to classification had not arisen. Fenestella intermedia 

 is clearly one of those connecting links between allied genera which, 

 while they serve to unite the family as a group, are somewhat difficult 

 to classify. Perhaps, on the whole, less violence will be done by 

 allowing F. intermedia to remain with the Fenestellce than by in- 

 cor])orating it with Polypora ; for I believe that Hall, in speaking 

 of his species, with its decided Po7//pora-affinities, is impressed with 

 its strong leaning to Fenestella. He says : — " It is the only species 

 of Polypora that has fallen under my observation in this geological 

 period ; and its characters are probably more analogous to those of 

 Fenestella than are those of the Carboniferous period. Polypora 

 incepta (Hall) probably shows the first departure from the character 

 of true Fenestella" '\. The latter position may now more truly be 

 claimed for Fenestella intermedia. 



Locality. Wenlock Limestone near Dudley. 



I may observe that, in describing these species of Fenestella, I 

 have endeavoured to do so from the best-preserved specimens 

 obtainable, and that, after the examination of some hundreds of 

 examples, I have not succeeded in procuring all the evidence with 

 regard to certain details of structure that I could wish. For instance, 

 I have no doubt that the keel of Fenestella reteporata possessed the 

 usual spiny appendage. As yet I have not succeeded in tracing it. 

 The same remark will apply to other details. A general caution is 



» Hall's Pal. New York, vol. ii. pi. 40 d. fig. 5. Ibid. p. 167. 



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