COASTS VISITED BY THE ARCTIC EXPEDITION. 623 



their constant occurrence together in close proximity, and also that 

 some of the fragments are so fractured as to show the gradual pas- 

 sage from the broad flat interstice of the obverse to the narrower 

 and more convex stems of the reverse. The broad depressed inter- 

 stices are well shown in the enlargement of Count von Keyserling's 

 figure and in that given by Dr. Geinitz. The fenestrules, as seen on 

 the obverse face, are nearly elliptical ; but there is apparently a ten- 

 dency to close up caused by a widening-out of the depressed inter- 

 stices, so that their form becomes more and more contracted laterally 

 and slit-like, till at last almost complete coalescence of the inter- 

 stices takes place and the fenestrules nearly disappear. Further- 

 more, on some parts of the polyzoarium the apertures of the cells 

 appear to close up ; and when this takes place, in addition to the 

 impinging of the interstices on the fenestrules, we have presented to 

 us a surface unbroken except by the remains of a few obscure slits 

 arranged in vertical lines. On the other hand, when the cells remain 

 open, the apertures are clear and well marked, but without raised 

 margins. The dissepiments on the obverse are very short, and as 

 the gradual closing of the fenestrules takes place, their individuality 

 is quite lost ; they are sometimes celluliferous to the extent of one 

 or two cells. 



Now many of the points here mentioned, although not described 

 by Keyserling and others, are nevertheless to be seen in their figures. 

 Eor instance, the broad, almost flat interstices, the gradually disap- 

 pearing dissepiments, and the obscured fenestrules are all, to a 

 certain degree, discernible in the before-mentioned enlargement of 

 Keyserling's figure. After a lengthened examination of the speci- 

 mens, and careful consideration of all the facts, I believe Polypora 

 biarmica is better fitted for the reception of several of the Arctic 

 Polyzoa possessing the above characters than any other figured 

 species known to me. The specimens in question resemble P. biar- 

 mica in the breadth of the interstices being equal to and sometimes 

 greater than that of the fenestrules, in the number and arrangement 

 of the cells and in their plain margins, in the oval form of the 

 fenestrules, and, lastly, in the fact that, as Keyserling remarks, the 

 latter are sometimes so narrow as to be almost overlooked, a 

 point which I consider quite coincides with the closing of the fenes^ 

 trules which I have above described. On the other hand, the sides 

 of the fenestrules are certainly rendered irregular by the impinge- 

 ment over them of the lateral row of cell- apertures on each side, 

 which I do not find mentioned or figured by those authors who have 

 written on this species. Again, in our specimens there is certainly 

 no trace of the obscure and slightly granular wrinkles of the reverse 

 mentioned by Keyserling ; but, on the whole, I think the evidence is 

 more confirmatory than otherwise of their relation to P. biarmica. The 

 best of our specimens, exhibiting the reverse face, agrees exceedingly 

 well, in the round or oval form of the fenestrules, with the figure of 

 the specimens from Nova Zembla given by Dr. Toula, and to a certain 

 extent with that of Polypora Shumardiana, Prout* ; but it must be 

 * Trans. St. Louis Acad. i. p. 271. t. 16. f. 3. 

 Q. J. G. S. No. 135. 2 t 



