184 



The avicularia, which vary considerably in size, may sometimes attain the 

 size of the zocEcia, and their distal opercular part protrudes often sharply, some- 

 times almost vertically from the surface of the colony. 



Spicules: The length of the rather slender curves varies between 0,026 and 

 O.llS""-, of the compasses between 0,066 and 0,33"""- 



Of this form I have examined a number of colonies from Torres Straits 

 (Haddon), belonging to the Museum of Zoology at Cambridge. Some of these are 

 incrusting, others make free, partly hollow expansions of one layer, and still 

 others consist of a number of very differently shaped, partly two-layered and flat, 

 partly C3'lindrical segments, which are movably joined by chitinized belts of a 

 dark colour (fig. 1 a). 



Var. D. (gothica). 



Membranipora gothica Busk; 



The zooecia are of an elongated, hexagonal, rounded form, and their length 

 is from 0,59 — 0,79™™ The aperture, the length of which may be contained 

 2V2 — 3 times in the whole length of the zooecium, has a broad and deep, some- 

 times trapeziformly rounded sinus and takes up so great a part of the breadth 

 of the zocecium, that the adoral areas are much reduced or completely wanting. 

 No spines. The two opesiulse are only separated from the aperture by a narrow 

 bridge, and but the one opesiular outgrowth reaches the basal wall, which it 

 meets in a generally rather shoit line, bent like a hook. Numerous and partly 

 rather large pores. 



Spicules. The length of the curves is between 0,039 and 0,079'"™- and of 

 the compasses between 0,093 and 0,305'""''; as however most of the zooecia 

 were without operculum, and a great deal of the spicules appeared to be absent, 

 the limits of the dimensions may prove to be somewhat wider. 



Of this form I have had the opportunity of examining a piece of Busk's ori- 

 ginal specimen from Mazatlan, for which my best thanks are due to the Director 

 of the British Museum. 



Var. E. (californica). 



(PI. VI b, figs. 2a-2d). 

 The length of the zooecia is between 0,59 and 0,80""" and that of the 

 aperture may be contained 3 — 3^2 times in the entire length of the zooecium. 

 The two adoral areas may be level or provided with acropetal spines which are 

 sometimes very small. But one of the two opesiular outgrowths and only in about 

 half of the zooecia, reaches the b^sal wall, which it joins in a very short, ascen- 



