400 ME. A. W. WATERS OK THE 



Cloaure of the Cyclostomatous Bryozoa, 

 By Aethue Wm. Watees, F.L.S., F.G-.S. 



[Eead 20th March, 1884.] 



(Plate XVII.) 



As my description of tlie Australian fossil Chilostomata pro- 

 gressed, I have known that the Cyclostomata must shortly be 

 dealt with, and have looked forward to this with feeling almost of 

 dismay, because the Cyclostomata possess so few characters that 

 can be used for the purposes of determination. In consequence, for 

 some time sections of such Cyclostomata as were available were 

 prepared and examined, to see what other points might be used 

 for the purpose. Although the results are very small in pro- 

 portion to the amount of work, yet I shall in my forthcoming 

 paper to the Geological Society be able to point out that the 

 ovicells ought to be very carefully examined, as there are more 

 points of importance than have so far been used, and shall call 

 attention to the connecting pores being comparable with the 

 rosette-plates of the Chilostomata, and giving, by their j)ositiou, 

 useful characters. Stress must be laid upon the size of the zooe- 

 cial tube, as this, as already pointed out by Smitt, seems to be 

 constant in each species. The range in size of the zooecial tube 

 is not very great ; the smallest being only 0'03 millim., while some 

 are nearly 0*2 millim. ; but it is quite exceptional to find zocecia 

 more than 0"14 millim., or less than 0"07 millim. 



Besides these, there is another character which has never been 

 understood and is quite neglected, and which may possibly be of 

 great use ; but to what extent, it is impossible to say at present. 

 I refer to the position of the closure of the zooecial tube. As a 

 correct understanding of it has a most important bearing not 

 only upon a large number of living species, but also on several 

 groups of fossils, some of which are still of a more or less pro- 

 blematic character, I am anticipating my descriptive paper by 

 dealing with this at present, in order that it may be more 

 fully studied from various stand-j)oints by those who have the 

 opportunity. 



In the ' Crag Polyzoa,' p. 110, Mr. Busk speaks of the mouths 

 of the tubes of Mesenteripora being eventually closed by a cal- 

 careous lid having usually a minute central perforation. Smitt 

 figured the cover with a projecting tubule in what he called 



