19 



Affinities. 



As to the affinities of the present division there can be no doubt that the Meli- 

 cerititidae are Cyclostomata, and in the first place tliis is distinctly shown by the 

 form and development of the zooecia, these being long slender tubes each of which arises 

 from the proximal part of another zooecium. The presence of numerous fine pores is 

 also a cyclostomatous character, and rhombic or hexagonal zooecial areas divided 

 by prominent marginal ridges may also be found in a number of Cyclostomata. The 

 gonozooecia are provided with similar ooecial expansions as are found in the Cyclo- 

 stomata, and the superficial layers of growth above spoken of are also found in a 

 number of cyclostomatous species, but never in the Cheilostomata. The only two 

 characters which might speak in favour of Cheilostomatous affinities are the pre- 

 sence of an operculum and of heterozooecia. Apart from the fact that the latter 

 as the common zooecia are long slender tubes they differ from the cheilostomatous 

 heterozooecia in possessing calcareous mandibles and in lacking a membranous 

 suboral area. The opercula are also calcareous while the opercula in the great 

 majority of the Cheilostomata are chitinous, a calcareous operculum being only 

 present in a few clieilostomatous species. Therefore we must regard the presence 

 of opercula and of heterozooecia as a case of parallel development. 



We here propose to divide the Ordre Cyclostomata in two subordres, the Cyclo- 

 stomata inoperculata and the Cyclostomata operculata, and the latter may be defined 

 in the following manner. 



Cyclostomata opeiTulata. 



Cyclostomata the zooecial tubes of which are much widened distally appearing 

 on the surface of the colony as hexagonal, rhombic or qvadrangular mostly con- 

 cave areas, in most cases divided from each other by a meshwork of ridges, in 

 the knots of which are very often seen more or less developed tubercles. The sub- 

 terminal aperture which has a straight or almost straight proximal margin is pro- 

 vided with a convex calcareous operculum showing more or less distinct radiating 

 striae. In most species are found heterozooecia the aperture of which is very often 

 of a similar form as that found in the cheilostomatous avicularia. They always 

 lack a membranous subopercular area and are provided with a calcareous mandible. 



Family Melicerititidae Pergens. 

 Eleidae d'Orbigny. 



The family Melicerititidae has been divided by d'Orbigny in 11 and by Gre- 

 gory in 10 genera, and the generiijue characters have been taken partly from the 

 form and mode of growth of the colony partly from the presence or absence of 

 heterozooecia (avicularia). As to my opinion none of these characters are sufficient 

 to serve as base for a generic division, and I have not yet been able to distinguish 



3* 



