126 



length of the zooecium (up to 18 on each side), one or two pairs of spines on 

 the distal part of the zooecium, typical avicularia, the ooecia immersed in the 

 avicularia. 



A form from Victoria. The spine-like processes are much reduced and cannot 

 be seen from the surface of the colony, appearing merely as small knobs. They 

 seem also sometimes to be in very small numbei's. Broad, flat, pointed spines 

 appear in the whole length of the zooecium. Typical avicularia, the ooecia 

 immersed in the avicularia. The form which Busk^ described in 1852 differs 

 from the last mentioned in that the teeth are well-developed and the spines 

 partially widened at the tip, with two or three branches. 



Very close to S. denticulata is S. florea, which has well-developed, hook-shaped, 

 denticles, 1 — 2 spines, typical avicularia and the ooecia immersed in the avi- 

 cularia, whilst the ooecia are immersed in the ordinary zocecia in S. dentigera, S. 

 spinuligera and S. serrata^, the last of which lacks the denticles, unless, as in 

 the above-mentioned species from Victoria, they are here also so small that they 

 cannot be seen from the surface of the colony. This last species, in which the avi- 

 cularian mandible is much more beak-like than usual and elongated, is very variable 

 in regard to its armature, as within the same colony we can find zooecia with 1 — 2 

 or with numerous spines, widened at the end and branched two or three times. 



The above diagnosis has been designed so as also to include ^ Membraniporat 

 flustroides and Fl. octodon^, but the connection of these two species, and especi- 

 ally the last, with the others is not without some doubt. Instead of the typical, 

 beak-shaped, elongated avicularian mandible they have rounded ones, and in the 

 case of Fl. octodon it is really only the elongated form of the zooecia and the 

 possession of, for a Flustra, an unusually large number of spines, which can be 

 taken as in favour of its relegation to the genus. Besides the presence of nume- 

 rous rosette-plates and spines, the fact that some of the ooecia are enclosed in 

 avicularia, a character not found outside the genus Spiralaria, is in favour of 

 the relegation of M. flustroides to the genus. 



Retiflustra n. g. 



(PI. I, figs. 6 and 7, PI. XXI, flgs. 1 and 2). 



The distal wall, at any rate in the ooecia-bearing zooecia and in most cases 



also in the others, meets with the basal wall of the colony in an angularly bent 



or curved line; the free edge of the ooecia, which are placed on the frontal side 



of the colony, is much lower than their basal edge; the zooecia have no spines; 



' 2, p. 49. ' 61, p. 131 and 64, p. 3. ' 2, p. 49. 



