269 



and with a well-chitinized compound operculum they must, I think, be referred 

 to the Malacostega, being most nearly related to the genus Callopora. The species 

 hyalina which Waters' with some doubt refers to the genus Megapora has be- 

 sides 6 larger, distal, marginal spines 1—3 very small, seated outside the frontal 

 area about half-way down, and as the second species M. ringens has an aperture 

 of quite the same form as that found in C. Poissoni, I think that these two spe- 

 cies are more nearly related to this interesting form than any other species hitherto 

 described. 



Having only examined dry colonies I have not been able to find a covering 

 membrane, but as the very low side-walls of the zooecia, when isolated, are sep- 

 arated from the arched frontal wall by an impressed line, I cannot doubt, that 

 this line indicates the distinction between a marginal gymnocyst and a frontal 

 cryptocyst, and as the spines arise just proximally to this line they are not, as I 

 originally thought, acropetal but marginal which can also be seen by a com- 

 parison with the ancestrula. 



Family Euthyridae. 



The zooecia are provided with a slightly calcified cryptocyst, and in a larger 

 or smaller part of their surface the surrounding covering membrane is kept 

 distended by ridge-like or rod-shaped processes from the cryptocyst, which has 

 a number of superficial rosette-plates. The interzooecial walls have scattered, 

 uniporous rosette-plates. A compound operculum. No spines and no heterozocecia. 

 There may be endozooecial ooecia with a projecting, membranous ectoooeclum. 

 Free, branched colonies. 



Summary of the genera. 



1) Ooecia occur; the aperture provided with a narrow sinus; (the 

 covering-membrane is everywhere kept distended by narrow ridges 



from the cryptocyst) Urceolipora Mac Gillivr. 



(Calymmophora Busk). 



1) No ooecia, but two different forms of zooecia; the aperture with- 

 out sinus, but with an almost straight proximal margin: 



2) The frontal cryptocyst forms a continuous calcareous surface; 

 the covering-membrane is on the frontal as well as on the basal 

 surface distended by means of rod-shaped processes from the crypto- 

 cyst Eathyris Hincks^. 



' 115, p. 39, 102. ^ 27, p. 164. 



