REPORT ON THE MONAXONIDA. 233 



dermal reticulation, where they reduce the dermal membrane to a mere network ; diameter 

 about 0'05 mm. 



Skeleton. — Very diffuse and with only very slightly developed spiculo-fibre ; con- 

 sisting of thickly but irregularly scattered tylostylote spicules, sometimes arranged in 

 tracts ; towards the surface the skeleton becomes much denser so as to form a kind of 

 cortical layer. This is most strongly pronounced in the mammiform processes, where it 

 consists of a very dense reticulation of interlacing spicules. The cortical layer is, however, 

 much broken up by the large, irregularly shaped, subdermal cavities, and it is not very 

 sharply marked off from the deeper skeleton. At the surface of the sponge are irregular 

 brushes of smaller tylostylote spicules whose apices project for a short distance beyond 

 the dermal membrane. 



Spicules. — (a) Megasclera; (1) the main spicules; straight or slightly curved, gradually 

 and sharply pointed, fairly stout tylostyli (PL XLV. fig. 11), with well developed, 

 broadly oval heads; size about 0-5 by 0"0157 mm. (2) The spicules of the surface 

 brushes ; smaller, straight, slender tylostyli (PI. XLV. figs, llo, lib), commonly with well 

 developed, broadly oval heads and gradually and finely pointed apices ; size about 0"3 by 

 O'OOS mm. (h) Microsclera ; stout spined spirulge (PL XLV. figs, llc-llg), consisting 

 each of three or four bends and with abundant strong spines ; size, exclusive of spines 

 about 0'5 by 0*009 mm.; smaller ones of rather different appearance are also abundant, 

 but they are probably only young forms of the larger. These S23icules occur in very great 

 numbers in the dermal membrane and for a short distance below it. 



The jDeculiar warty appearance of the surface seems to be the most characteristic 

 feature of this species, but, owing to information received from Dr. R. von Lendenfeld, 

 we are doubtful whether this will turn out to be a constant character. 



Locality. — Port Jackson; depth, .30 to 35 fathoms. One specimen. 



Genus Latrunculia, Bocage (Pis. XXIX., XLIV., XLV.). 



1870. Latrunculia, Bocage, Jorn. Acad. real. Sci. Lisboa, vol. ii. p. IGl. 



1875. ScepireUa, Hchmidt (jMi-fi), J ahi'dsb. Comm. wiss. Unters. deutscli. Meere, Jahrg. ii.,iii. p. 119. 



Sponge massive, sessile, usually corticate. Upper surface usually covered with 

 mammiform projections. Megasclera smooth styli (? or oxea). Microsclera discastra, 

 characteristic of the genus and typically forming a dense dermal crust. 



The numerous small mammiform processes are very characteristic of this genus ; some 

 of these bear oscula while others are raised pore-areas ; we cannot, however, say whether 

 this arrangement obtains in all species. 



Bocage {loc. cit.) gives no attempt at a generic diagnosis but plunges at once into the 

 description of the type species, Latrunculia cratera. Previous to the appearance of our 



(ZOOL. CHALL. EXP. — PART LIX. — 1887.) Nlin 30 



