194 



often divided by sutures into four segments, ascending towards the margins of the 

 zocecium, namely, a distal, a proximal and two lateral, joining each other in a 

 short sutural line. It is however not uncommon that an area fuses with a con- 

 tiguous one, as e. g. the proximal area and a lateral one in fig. 4 a. While the 

 proximal area and the two lateral are more or less closely set with small scat- 

 tered pores, the distal one is only furnished with small tubercles, which are most 

 numerous just proximally to the aperture. 



Spicules. Besides curves, the length of which is between 0,026 and 0,113™"-, 

 a peculiar intermediate form occurs, with two unequally long arms, of which 

 the longer is formed as an arm of a curve while the shorter is like that of a 

 compass. Their length varies from 0,106 to 0,46™™- 



Ooecia are not found. 



The avicularia, of which none were found on the piece examined, are accor- 

 ding to Hincks rather uncommon, very small and with a triangular mandible. 

 Judging from the figure there is a calcified transverse bar between the opercular 

 and the subopercular areas, a character not found in any of the other species. 



Besides a fragment of the original specimen, which I owe to the kindness of 

 Mrs. H. Eden (nee Gatty), I have examined a small colony from Port Phillip 

 Heads, Victoria, sent me by Mr. J. Gabriel. 



Thalamoporella mamillaris Lamx. 



Membranipora mamillaris Hincks, Annals Nat. Hist., ser. 5, Vol. VI, 



1880, pag. 88, PI. X, fig. 9. 



(PI. VI a, figs. 5 a— 5 e). 



The length of zooecia varying between 0,532 and 0,665'"'"- The aperture, 

 the length of which may be contained "3 — 4 times in the whole length of the 

 zocecium, is bounded by two, more or less convergent lateral margins and by 

 an almost straight proximal margin. The horizontal basal pai't and the ascending 

 frontal part of the distal wall are not sharply delimited, and an oral shelf is 

 wanting. But some way within the free margin of the aperture and parallel with 

 it is a very narrow, low, glistening, usually beaded arch. The operculum, the 

 arch of which appears to be situated immediately within the free margin, has a 

 proximally incurved, extremely narrow chitinous sclerite, but the part of the 

 covering membi-ane between the operculum and the distal margin of the crypto- 

 cyst is more chitinized than the rest of this membrane and is thus connected with 

 the real operculum to a continuous whole. The two distinctly marked adoral 

 areas are well-developed and have large, compressed, conical acropetal spines. 

 Only one tongue-shaped opesiula is found, the direction of which is obliquely 



