Sponge-fauna of Norway. 397 



How far other distinctive characters will be found con- 

 stantly associated with those given as diagnostic of the genus 

 Isops, one cannot at present say. As yet only a single repre- 

 sentative of the genus (I. Phlegrcei) is known to me; between 

 it and Geodia Barretti, however, very characteristic differences 

 exist. Thus the former does not possess any of the small 

 acerate spicules, which, projecting erectly from its surface, 

 form the fine superficial down of G. Barretti; they appear to 

 be entirely replaced by the large long-shafted spicules which 

 form the externally projecting fascicular ends of the internal 

 spicular fibres. The trifid heads of the long-shafted spicules, 

 moreover, do not, as in G. Barretti, apply themselves with 

 horizontally extended rays to the inner surface of the globate 

 layer, but, projecting forwards, penetrate and terminate within 

 the globate layer. At present, however, it is uncertain whe- 

 ther these characteristic differences are generic or specific 

 merely. 



Isops Phlegrcei* } n. sp. 



Sponge more or less spherical, about 1 inch in diameter ; 

 surface hispid (when unworn) by the protrusion of long-shafted 

 spicules for about 0*15 inch beyond it ; when the spicules are 

 worn away the surface is smooth and of a faint greyish colour. 

 Excui-rent and incurrent ostia simple, numerous, scattered. 

 Each ostium a small round or oval opening, situated on the 

 summit of a conical elevation, which is very variable in size, 

 but always minute, the largest measuring 0*125 inch in 

 diameter at the base, and 0*025 inch at the summit; in some 

 cases the elevation may be almost entirely absent, the ostium 

 then lying flush with the general surface of the sponge. 

 Over some parts of the surface small white spots occur, some 

 of which are really and some only apparently imperforate, the 

 latter showing a minute central aperture on magnification. 

 These are the smallest ostia present ; between them and those 

 of the largest perforate monticule we have others of every 

 intermediate size. 



Skeleton. — The skeleton consists of long-shafted spicules, 

 globates, and stellates. 



Thick long-shafted Spicules. — (i) a simple, sharp-pointed, 

 fusiform acerate, 024 inch long by O0025 inch broad 

 (PI. XVII. fig. 5) ; (ii) a trifid spicule with simple, forward- 

 projecting rays, shaft OIG inch long, 0*0017 inch broad, rays 

 0-025 inch long (PI. XVII. fig. 7) ; (iii) a trifid spicule, with 



* In reference to the ostial elevations of its surface, reminding one of 

 the Cainpi Phlegnei. 



Ann. if* Mag. N. Hist. Ser. 5. Vol v. 27 



