6P0NGIIDA. 383 



and the greater number of cored primaries. Spongia cavernosa, 

 Esper, differs from both in having the surface between the canals 

 echinated with tufts. 



The peculiarly smooth and unbroken character of the surface of 

 the skeleton between the openings of the excretory canals appears 

 to be due mainly to the remarkable modification of the usual posil ion 

 of the uncored primary fibres, by which, instead of running parallel 

 to the cored primaries, and so meeting the general surfaco at right 

 angles and (as is usually the case) by a superficial projection, they 

 run approximately at right angles to the very scanty cored fibres, 

 and so parallel to the general surface of the sponge ; the very close 

 interstitial network further adds to its density and evenness of the 

 texture. 



STELOSPONGUS. 



Stelospongos, Schmidt, Atl. Gab. p. 29 ; Hyatt, Mem. Bost. Soc. ii. 



pt. 3, p. 528. 

 Polyfibrospongia, Bowerbank, P. Z. S. 1877, p. 459. 

 Stelospongia, F. E. Schtdze, Zeitsch. wiss. Zool. xxxii. p. 613. 

 Stellospougia, Marshall, Zeitsch. wiss. Zool. xxxv. pp. 00, 118. 



I cannot see any sufficient reason for Marshall's mode of writing 

 the name of this genus. The first part of the word appears to be 

 based on ot>')\i], a column, from the frequency with which Schmidt 

 alludes to the columns (" Siiulen ") formed by the main fibres of the 

 skeleton. 



0. Stelospongus excavatus. (Plate XXXIX. fig. A.) 



A small spirit-specimen, obtained at Port Molle, Queensland, has 

 a head which arises from a short pedicel, is broad and semitruncate 

 above, and cup-like, being excavated on its upper surfaco by four 

 pits, the deepest occupying a great part of the thickness of the sponge ; 

 each pit contains a vent : the vents vary in size from about -25 to 3 

 millim. The colour in spirit is greyish white (putty colour) ; the 

 dermis conceals all the skeleton but the ends of the primary fibres, 

 which appear as low points over the whole of the outer surface 

 and just inside the margins of the pits. 



The skeleton-lines measure about "38 millirn. in diameter, the 

 individual fibres of primary lines from '018 to -028 millim. in 

 diameter, those of the large secondary lines -07 millim. Both the 

 secondary and primary fibres enclose more or less foreign matter, 

 which also occurs on the outside of the primary fibres and dermis, 

 forming a kind of mosaic. Greatest height and breadth of the 

 single specimen 31 and 25 millim. respectively. Several large nu- 

 cleated and unsegmented ova are discernible in the tissues, scattered 

 or aggregated in groups of two or three ; the diameter of the largest 

 is about -06 millim. ; one was also observed which had apparently 

 divided into four segments. 



A fine dry specimen, 300 millim. in gross height by 95 in the maxi- 

 mum diameter of the cup, provided with a slender pedicel 150 millim. 

 long, breaking up below into a number of long stringv rooting 



i 



