HYDROIDA. BALE. 267 



complete turn of the stem, the fifth being in line with the 

 first. There are some irregularities, and as the hydrothecse 

 are nearer to those next them than to those above and below, 

 the quadriserial arrangement is not conspicuous. 



The hydrothecse are not of the slender, round-based, flask- 

 like form shown in the original figure, they are on the con- 

 trary rather stout, and when the free portion is short they 

 resemble those of a typical Thuiaria. They vary notably in 

 the length of the free portion ; in some fragments of the 

 'Challenger" type, for which I have to thank Dr. Kirk- 

 patrick, it is very short ; in the " Endeavour " specimens it 

 is often fully one-third of the entire length. This takes no 

 account of the increase by regenerations, which in the 

 "Endeavour" specimens is very considerable, as it also is 

 in the " Challenger " specimen figured by Billard. Allman's 

 description of the hydrothecse as having a " small circular 

 even orifice " is inaccurate. The fact is that the delicacy and 

 collapsibility of the perisarc at the orifice, together with the 

 confused appearance caused by the remains of successive 

 renewals, makes it generally difficult to determine the original 

 form. Billard concludes that it is probably bilabiate. After 

 examining many hydrotheca?, I have been able to fully satisfy 

 myself in several cases that the border has three deep emargi- 

 nations, between which it forms triangular sharp points. 

 The aperture, as seen on looking directly into it, is somewhat 

 triangular, but with the angles more or less rounded off, and 

 one marginal point is at the top, and the other two at the 

 lower corners. In the lines marking successive renewals, the 

 points only are usually obvious, and the upper one often less 

 so than the others. In the best specimens the three-valved 

 operculum was very distinct. It will be apparent that the 

 form of the aperture and the operculum is practically the same 

 as in a typical Sertularella, such as S. divaricata, differing only 

 in the extreme delicacy of the perisarc and in the slightly 

 deeper emarginations. 



The peduncles of the gonothecae do not spring from the 

 axils, as shown in Allman's figure. The gonotheca is erect and 

 central between the two branches at a bifurcation, but the 

 peduncle springs laterally from one of the branches, a little 

 above the axil ; it is noteworthy also that in all the portions 

 of colonies examined all the gonothecse spring from the same 

 side of the bifurcations. 



The frill-like appendages surrounding the gonotheca are 

 very wide, and as Billard has noted, they are strengthened by 

 numerous radial internal thickenings. Surrounding the upper 



