274 Proceedings of the Royal Physical Society. 



these specimens, I have endeavoured to obtain access to the 

 types of Lonsdale's species of Fenestella, forming a portion of 

 the collection formed by Dr Darwin, F.R.S., and described in 

 his work on "Volcanic Islands." Unfortunately these are 

 not now forthcoming, and appear to have been altogether lost, 

 so that for the future the determination of these species must 

 always remain on an unsatisfactory basis. An exception 

 to the unsatisfactory state of things amongst the Queens- 

 land Polyzoa exists in the form of a much crumpled, con- 

 torted, and curled polyzoarium of large extent, easily recog- 

 nisable by its strongly marked characters, when seen in the 

 form of casts. In this particular it is clearly allied to the 

 typical condition of Fenestella ampla (Lonsdale), . but differs 

 essentially in the perfectly circular form of the casts of the 

 fenestrules, their quincuncial arrangement, and wide separa- 

 tion from one another, thus denoting a large extent of inter- 

 stitial surface on the stems and branches. 



The next example in regard to the size of its constituent 

 parts is what at first sight might be taken for Lonsdale's F. 

 ampla, but on a critical comparison with the figures given in 

 Count Strzelecki's work, it will be observed that the casts of 

 the fenestrules are smaller and very much closer together 

 than in the latter. The difference between the size of the 

 fenestrules as represented by their casts and the distance of 

 one from the other in the two specimens will become ap- 

 parent at once. So far they are distinct, but there are in the 

 British Museum Collection intermediate forms so intimately 

 uniting these by insensible gradations that I hesitate to 

 separate them, notwithstanding the noteworthy points of 

 difference between the two extremes. It may not be out of 

 place to mention that the smaller form agrees very much 

 better with Professor De Koninck's representation of Fenestella 

 ampla than with the late Mr Lonsdale's, from which De 

 Koninck's figure differs in many particulars. 



The third and last form we have to deal with possessed a 

 frond still finer in the mesh than the preceding, the fenes- 

 trules being very much closer together and almost round. 

 As it stands by itself, it is quite separable from any of the 

 others, yet there are here, as in the former case, a number of 



