325 



in a less strongly chitinized, disc-like part, which fits into the bottom of the 

 sinus. Distally to this the accessory part is on each side provided with a longi- 

 tudinal thickening. Each distal wail is provided within its basal margin with 

 ca. 10 and each lateral wall in its distal half with ca. 5 uniporous rosette- 

 plates. 



The ooecia are of enormous size, equalling the smaller zooecia in length with 

 at the same time a breadth up to one and a half times that of the zooecia. They 

 are almost spherical and their very thick wall is mainly composed of a tuber- 

 culated net-work of ribs, with numerous scattered pores at the bottom of the 

 meshes. They quite cover the distal half of the zooecium to which they belong 

 (as well as the proximal half of the distal zooecium), and this is only seen on 

 removal of the frontal wall of the ocecium. Such an ooecium must therefore 

 during its formation send down a part on each side outside the respective avi- 

 cularium, and these two parts meet proximally to the zooecial aperture. The 

 semicircular ooecial opening which cannot be seen fi'om the frontal surface, is 

 partially closed by two finger-shaped prolongations almost meeting at the tips, 

 which spring from the two corners of the opening. There can here be no doubt 

 that the eggs must pass directly from the zooecial aperture into the ooecium 

 (see pag. 67). 



The avicularia appear in two different forms, the one of which has an elong- 

 ated triangular, the other a lyre-shaped mandible. The former, which are of some- 

 what small size, appear on the single zooecia to a number of 1 — 5 and usually 

 on each side of the aperture, with the mandible directed obliquely outwards and 

 distally. On the others the mandible may point in different directions. The avi- 

 cularia with lyre-shaped mandible, which occur in much smaller numbers, are 

 considerably larger, but vary however a good deal in size. In the basal part of 

 the colony, where they are equal in size to the zooecia, they always take the 

 place of the zooecia. 



The species occurs as incrusting colonies, which have superficial budding. 



West Indies, St. Thomas and St. John, 15—20 fathoms. 



A colony from Aor, Malacca, shows several differences from that just described. 

 Thus, the zooecia have as a rule only a single avicularium on the one side of 

 the aperture and the accessory part of the operculum has a similar form to that 

 in S. longirostris, but lacks the small border at the tip. 



