270 



2) The frontal cryplocyst is formed hy a iiuml)er of narrow, only 

 partially meeting ribs; the covering membrane is kept distended only 

 on the basal surface of the colony by means of the wedge-shaped, [)ro- 



jecting, central portion of the sei)arale zoo'cia Plciivoloichus n. g. 



(s|)ccies P. chillirdtiis Harmer'). 



Urceolipora nana Mac Gillivr. 

 Urceolipora nana Mac Gillivray, Transacl. and Proceed. Royal Soc. of Victoria, 



Vol. XIII, 1881 (for 1880), pag. 85, PI. (with- 

 out number, pag. 88), figs. 3 a — 3 c. 

 Calymmophora lucida Busk, Challenger, Zoology, ^'ol. X, Pari I, 18S4, pag. 82, 



PI. XXX, fig. 3. 

 (PI. XV, figs. 1 a— 1 f). 



The zocecia, which increase greatly in extent from (he narrow proximal to- 

 wards the distal end, have in the greater part of their length an oblong, oval 

 transverse section (tig. 1 c) and when seen from the frontal or basal surface Ibeir 

 form is somewhat vase-like (figs. 1 b, 1 d). The distal end of each zooecium projects 

 a great deal over the i)roximal |)arl of the higher j)laced zocrcium with which it 

 forms an acute angle. The covering membrane is kept distended from the cryplocyst 

 by a number of narrow longitudinal ridges, which spring from the latter, but 

 which arc dilTerenl on the two surfaces of the branch. To begin with, there is on 

 both surfaces of the branch a zigzag longitudinal ridge, which runs in immediate 

 proximity to the suture between the two rows of zocecia (fig. 1 e) and is situated 

 in each zoa^cium on the part which lies between its own distal wall and thai of 

 the lower placed, opposite zoo'cium. This zigzag ridge, which is most strongly 

 developed on Ihe side of the branch turned away from the twin-branch (the 

 abramal side of the branch), is in each of the oa'cia-bearing zocEcia continued 

 into a collar-shaped, vertical part (figs. 1 a, 1 d) situated at the base of the o(r- 

 cium, while in the ordinary zott'cia it is continued into the angle belween two 

 succeeding zocecia of the same longitudinal row. The two ridges from the oppo- 

 site sides of the zooecium are liere joined into a single one, which ends in the 

 distal margin of the aperture some way from the central line on the abramal 

 side of the aperture. On the adramal side of the branch each zooecium is more- 

 over in the greater part or in the whole of its length provided with a strong, 

 somewhat curved longitudinal ridge (fig. 1 a), which is somewhat different in the 

 zocEcia arising from oa>cia-bearing zoo-cia and in those springing from non-o(ccia- 



' 19, p. -Jdf). 



