107 



The colony examined consists of c. 20 zooecia-bearing main trunks, of which 

 the longest have forty odd segments and a length of 16.5 ctm. The segments 

 have a length of 3—5 mm. 



Christiansted lagoon, St. Croix (Fishery Inspector Mag. Chr. Lefting). 



Dimorphozoum nov. gen. 

 The colony consists of two layers, the zooecia of which are of exceedingly 

 diverse nature. In the one layer (the Ctenostome) they are quite uncalcified and 

 have no operculum, whilst in the other (the Cheilostome) they have an oper- 

 culum and the structure general in the family. The last layer has besides the 

 following characters: the distal wall consists of a basal horizontal portion with 

 a multiporous rosette-plate, and of a frontal ascending portion; free ocecia; freely 

 movable, club-shaped avicularia. 



D. nobile (Hincks). 



Flustra nobilis, Hincks, Annals nat. hist. 6 Ser. 

 Vol. 7, 1891, pag. 288, PI. 6, fig. 5. 



Waters Journ. R. micros. Sec. 1896, 



pag. 281, PI. 7, fig. 10—11. 

 (PI. IV, figs. 1 a-1 f). 



The Cheilostome lager: 



The zooecia are elongated hexagonal, and the frontal wall membranous in al- 

 most its whole extent. The distal edge furnished with 4 spines, which may vary 

 considerably in size, and of which the middle ones are the longest. When they 

 are not very small, each one of them sends out a small, distally directed branch 

 from its proximal half. There are as a rule 4 — 6 bifurcated spines on the distal 

 half of each lateral edge, which also varj' considerably in size. The inner branch 

 is generally the longest, and may occasionally reach more than half-way over 

 the frontal area, it may also however be quite absent. The distal wall ends 

 basally in a straight edge, and there is generally a more strongly calcified belt 

 (fig. 1 d) both proximally and distally. It is provided with a very large, multi- 

 porous rosette-plate (fig. 1 c) and such is also found in the distal half of each 

 lateral wall (fig. 1 b)\ On the basal wall of a great many zooecia there are 1 — 4 



' When I give the number of rosette-plates (109, p. 281) in the distal half of the lateral walls it 

 is because in species with independent lateral walls it can easily be seen (p. 27) that the rosette-plates 

 (or at any rate their main part) as a rule belong to the distal half of the lateral walls, the proximal 

 part only possessing a corresponding number of openings, each surrounded by a pore-ring. In species 

 with common lateral walls only the rosette-plates in the distal half of a lateral wall have their con- 

 vexity turned inwards. 



