204 Mr. J. W. Kirkby on some additional Species 



them. And it should be mentioned that this is not my opinion 

 only, but that of Mr. T. Rupert Jones, to whom I submitted for 

 examination specimens of both the present species and the 

 preceding, each of which he referred to the Permian species 

 named. 



3. Fenestella retiformis, Schlotheim, 1816-17. 



Syn. Fenestella plebeia, M'Coy, 1844. 



Permian specimens, PL IV. figs. 13, 16, 17; Carboniferous 

 specimens, PI. IV. figs. 14, 15, 18. 



Among other Polyzoa that I have received from my Glasgow 

 friends are numerous specimens of a Fenestella, labelled F. ple- 

 beia, which so closely resembles F. retiformis of the Permian 

 rocks that I have no doubt as to both being the same species. 

 The specimens are from Beith, and occur, in a more or less frag- 

 mentary state, on the weathered surfaces of a hard dark-grey 

 limestone. Generally speaking, they are less robust than well- 

 developed Permian examples ; and many of them have scarcely 

 so many cells to the fenestrule as have normal specimens of the 

 latter. But some specimens have precisely the same number of 

 cells, which is about three to the fenestrule, or, rather, eleven to 

 the four fenestrules. Prof. M*Coy having described the species 

 from specimens possessing " four or five cells to the fenestrule," 

 this would seem to be a variable character, and one that cannot 

 be subjected to very exact comparison. In both Permian and 

 Carboniferous specimens the ribs or interstices have the same 

 relative strength compared with the dissepiments, and they 

 branch in the same way, and are connected by similar dissepi- 

 ments, which thus give to the fenestrules identity of form. 

 Both have the reverse or uncelluliferous face covered with mo- 

 derately coarse longitudinal striae ; and the cellule-apertures are 

 more or less circular in each. All the Carboniferous specimens 

 I have seen are somewhat worn, and do not show the raised 

 margins of the cellule-apertures, which well-preserved Permian 

 examples often retain, as represented in fig. 17: when worn 

 specimens of both are compared, no difi^erence is to be observed 

 in this feature. 



It is just possible that the Beith specimens may be erroneously 

 identified with Fenestella plebeia of M'Coy; for the figures of 

 that species in his 'Syn. Char. Carboniferous Fossils of Ireland' 

 certainly do not agree so closely with specimens of F. retiformis 

 as they. But, however this may be, there would scarcely seem 

 any doubt of F. retiformis being specifically undistinguishable 

 from the Beith specimens. 



