270 



2) The frontal cryptocyst is formed by a number 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, pro- 

 jecting, central portion of the separate zooecia Pleurotoichus n. g. 



(species P. clatbratus Harmer^). 



Urceolipora nana Mac Gillivr. 

 Urceolipora nana Mac Gillivray, Transact, 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, Vol. X, Part t, 1884, pag. 82, 



PI. XXX, fig. 3. 

 (PL XV, figs. 1 a— 1 f). 



The zooecia, which increase greatly in extent from the narrow proximal to- 

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

 transverse section (fig. 1 e) and when seen from the frontal or basal surface their 

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

 a great deal over the proximal part of the higher placed zocecium with which it 

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

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

 which are different 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 zooecia (fig. 1 e) and is situated 

 in each zocecium on the pai-t which lies between its own distal wall and that of 

 the lower placed, opposite zocecium. This zigzag ridge, which is most strongly 

 developed on the side of the branch turped away from the twin-branch (the 

 abramal side of the branch), is in each of the ooecia-bearing zooecia continued 

 into a collar-shaped, vertical part (figs, la, Id) situated at the base of the oce- 

 cium, while in the ordinary zooecia it is continued into the angle between two 

 succeeding zooecia of the same longitudinal row. The two ridges fi-om the oppo- 

 site sides of the zooecium are here 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 

 zooecia arising from ooecia-bearing zooecia and in those springing from non-ooecia- 



' 19, p. 266. 



