I!V E. F. HALLMANN. 785 



Lsociella flabellata Ridley and Dendy. 



(PI. xl., figs. 1, 2; and Text-fig. 3.) 



188G. Phakellia flabellata, Ridley and Dendy (16), p. 478. 

 1887. Phakellia flabellata, Ridley and Dendy (17), p. 171, PL 



sxxiv., figs. 2, 3, 3a; PL xl., figs. 6, 6a. 

 1897. Phakellia jacksoniana, Dendy (4), p. 236. 

 1907. Phakellia jacksoniana, Whitelegge (24), p. 507. 



External characters. — With respect to external features, the 

 previous description (17) of the species, based upon eleven 

 specimens, requires but little to be added to it. The sponge 

 (17, PL xxxiv., figs. 2, 3) is erect, flabelliforni, with a rather 

 short, cylindrical stalk terminating below in a flattened base of 

 attachment, and above expanding, usually more or less suddenly, 

 into a single, entire or lobately subdivided, vertical frond vary- 

 ing from 2 to 3 mm. in thickness. Not infrequently the frond 

 presents one or a few, usually more or less elongated, open 

 spaces or fenestrae, mostly of inconsiderable size, which are 

 evidently due to an incomplete concrescence of originally separ- 

 ate lobes; and sometimes (though very exceptionally) the lam- 

 ella remains subdivided into separate lobes almost to the apex 

 of the stalk. Of the specimens so far obtained the largest mea- 

 sures 180mm. in total height; the greatest breadth which the 

 frond attains in any specimen is 125mm.; and the stalk varies 

 in different specimens from 4 to 8.5mm. in greatest diameter 

 and up to 40mm. in length. Invariably the surface, on one 

 side of the frond is thrown into more or less prominent, rather 

 irregular, longitudinal furrows and ridges (the latter, in part, 

 sometimes discontinuous, and replaced by a succession of low 

 hummocks), while on the other it is comparatively smooth and 

 bears numerous minute oscula (rarely exceeding 0.5mm. each 

 in diameter) disposed in subcircular groups, with about from 8 

 to -12 oscula in each group. The subcircular areas occupied each 

 by a group of oscula vary from 4 to 6 mm. in diameter and from 

 6 to 10mm. in distance apart measured from centre to centre; 

 are usually slightly depressed below the general level of the sur- 

 face; and are fringed each by a series of more or less distinct, 

 radiating, short, shallow grooves, which give to them a stellate 

 aspect (17, PL xxxiv., fig. 3a) . The dermal membrane — accord- 

 ing to the previous description of the species — is thin and trans- 



