224 A MONOGRAPH OF THE 



interstitial membranes they appeared to be more frequently 

 dispersed than fasciculated. The form of the skeleton spi- 

 cula verv closely resembles those of Hymeniacidon clavigera, 

 but their bulbous bases do not appear to be exaxial, as in 

 that species. They are long and powerful, and the spination 

 does not extend beyond the base more than about a sixth 

 or a seventh of their whole length. The internal defensive 

 spicula are of the same form as the skeleton ones, but they 

 are entirely but minutely spined, and are not above one 

 fourth or one third the length of a full-sized skeleton spi- 

 culum. 



The expando-tridentate equi-anchorate spicula of the 

 sarcode are very characteristic of the species ; the teeth are 

 strongly produced, and the lateral ones widely spread ; the 

 shaft is very stout, and frequently curved to the full extent 

 of a semicircle. 



From the similarity of the skeleton spicula of this sponge 

 to those of //. clavigera, the two sponges might be readily 

 mistaken for each other, if it were not for the strikingly 

 characteristic forms of the anchorate spicula, which do not 

 occur in H. clavigera. 



38. Hymeniacidon Dujardinii, Bowerbank. 



Halisarca Dujardinii, Johnston. 



Sponge. Coating, thin. Surface smooth and even, gela- 

 tinoid. Oscula and pores inconspicuous. Dermal 

 membrane abundantly covered internally with dis- 

 persed skeleton spicula. Spicula of skeleton cylindrical, 

 long, very slender, and often flexuous. Internal de- 

 fensive spicula attenuato-acuate, basally and medially 

 spinous, large and stout; spines conical, large, and 

 very numerous at the base. 



Colour. Alive, ochreous yellow to deep amber colour. 

 Habitat. Berwick Bay, Dr. Johnston; Strangford Lough, 

 Dr. Dickie; Scarborough, Mr. Bean and J. S. Bowerbank. 



