4 C. M. Maplestone: 



Mr. Whitelegge further states that most of the published 

 figures of the zooecia are upside down. This is accounted for 

 by the extraordinary circumstance that the zooecia are really 

 upside down ; indeed, he admits as much Avhen he says " the 

 direction of the zooecia is also apparently reversed," and he 

 eays that the free distal edge of the operculum is directed to- 

 Avards the apex of a conical form. The free edge of the oper- 

 culum is directed towards the apex, but it is not the distal edge. 

 The fact is that the operculum is hinged at the distal edge, and 

 not at the proxinuvl one ; so that in these conical forms not 

 only are the zooecia upside down, but the operculum is also 

 uj)side down and in the specimens, in which the operculum is 

 not preserved (both fossil and recent) the sinus is. always in the 

 distal margin of thyrostome and not the proximal one, as in 

 other polyzoa of the family tSchizojJnrellidae (in which Dr. 

 MacGillivray placed the Biporae). To make clear what I mean 

 by saying the zooecia are upside down, take the case of the 

 other cheilostomes ; the zooecia are formed one beyond, or 

 above another, and the later formed ones rest upon, or are 

 joined to the earlier formed ones with the proximal end resting 

 upon or joined to the distal end of the preceding zooecium, and 

 the thyrostome is situated in the distal portion of the zooecium 

 with the operculum hinged at the proximal nuirgin opening 

 downwards. Now in the conical Biporae the zooecia folloAv 

 one another in a somewhat similar manner, but the zooecia 

 are in a reversed position : that is, what is the proximal, or 

 lower wall in the ordinary cheilostomes, is in them the distal or 

 uppermost, the thyrostome is in the proximal portion of the 

 zooecium, and the operculum is hinged at the distal margin 

 of the thyrostome opening upwards. The cause of this peculiar 

 reversal of the ordinary arrangement is unknown, but Professor 

 Harmer points out to me that it would seem to show " that 

 the polypide bud while in a young condition might get twisted 

 round 180 degrees in the zooecium." This probably is the 

 case, but, before twisting round, the polypide bud must have 

 in its growth extended itself to the end of the zooecium furthest 

 from the older zooecia before turning round and developing 

 into a mature form. Absolute proof of this cannot be deter- 

 mined until some spirit preserved specimens of living forms be 



