510 PROF. A. DENDY AND MISS L. M. FREDERICK ON 
The skeleton arrangement and spiculation agree with the descriptions 
given by Bowerbank and Topsent. 
Spicules: — (1) Small tylostyles ; size about 0"17 by O'OOSinm. 
(2) Large tylostyles; size about 1"1 by 0'02 mm. ; the size of the head 
varies greatly. 
Previously knoiun Distribution. Cosmopolitan. 
Register No. and Locality. VI. 12 d, Sandy Isle. 
44. Megalopastas aeenifibrosa n. sp. (PL 25. fig. 15.) 
There are three specimens of this sponge in the collection. The largest 
(R.N. VI. 3, PI. 25. fig. 15), which must be regarded as the type of the 
species, is sessile, erect, and consists of a principal lamella giving off a 
number of secondary lamellaj of varing size. The specimen is 110 mm. 
high and 70 mm. wide, and the thickness of the lamella is about 3 mm. 
The second specimen (R.N. VI. 9), which is 65 mm. high, 15 miii. wide and 
about 5 mm. thick, is a fragment probably broken off the type. The third 
siiecimen (R.N. IV. 4) is small and lamino-clathrous, becoming constricted 
towards the base of attachment. Tlie total height is about 50 mm., the 
maximum breadth about 55 mm., and the average thickness of the lamella 
about 4 mm. The surface appears granulated, the granules being really 
numerouSj minute, close-set conuli. The vents are small, round and single; 
some are arranged marginally, others are scattered, but almost always 
confined to one surface of each lamella. Colour in spirit dark brown, 
becoming lighter towards the base of the sponge ; texture compressible, 
resilient, fairly tough. 
The main skeleton consists of primary fibres, about 0'09 mm. in diameter, 
running vertically to the surface and connected by an irregular network of 
secondary fibres about half the diameter of the primaries ; the outermost of 
the secondary fibres form a distinct subdermal skeleton network, the fibres 
averaging about 0'03 mm. in diameter. The fibres are laminated and " pithed" 
and the primary fibres are cored by numerous sand-grains and broken 
spicules. 
The dermal membrane, which sometimes contains a good many broken 
spicules, is pierced by round inhalant pores, about 0'06 mm. in diameter, 
which lead into large subdermal cavities lying in the ectosome, which 
contains numerous close-packed, granular, stellate cells. The canal-system is 
lacunar ; the flagellate chambers, which are large, sac-shaped, averaging about 
0'05 mm. in diameter, are placed fairly close together and are eurypylous. 
The mesogloea of the choanosome is not strongly developed, except around 
some of the larger canals, where it is eoUenchymatous, with stellate cells. 
There are also numerous bands of fibrous tissue, composed of granular, 
elo igated cells, running in from the ectosome in places and deeply pene- 
trating the choanosome. 
This species is well characterised by its external appearance and unusually 
