REPORT ON THE HEXACTINELLIDA. 43 



The pentact pleuralia of Rossella antarctica (PI. LV. figs. 1, 7, 9) deserve special 

 notice. They arise from small conical elevations and project radially in bundles from 

 the outer surface of the Sponge, while their four tangential rays, which arise transversely 

 to the radials, extend at tolerably equal distances over the surface of the Sponge. The 

 tangential rays, which are provided with small prongs and a uniformly rough cortical 

 layer, do not intersect at right angles, but are so disposed at acute angles that the four 

 together enclose a right angle (PI. LV. figs. 9, 13). Between these pcntacts, which 

 also form a remarkable veil-Hke structure, other longer simple pointed radially pro- 

 jecting diacts occur. 



Marginalia. — In the oscular margin of numerous Lyssacina there is a circle of more 

 or less wddely projecting spicules — marginalia — which usually consist of elongated 

 diacts, in which the axial canal cross, which is often distinctly recognisable, or even 

 indicated externally by boss-like swellings, usually lies almost in the plane of the 

 outer skin. The projecting distal ray is for the most part thickly beset with outw^ardly 

 directed prickles and prongs ; it is less frequently quite smooth, and usually terminates 

 in a point, though sometimes in a small knob-like thickening (PI. L. fig. 4). The 

 internal, usually much shorter ray of the diact exhibits in some cases small proxi- 

 mally directed prongs (PI. XL. fig. 6), but is usually smooth and uniformly pointed. 

 The marginalia include those spicules which project freely in a cufi"-like fashion from 

 the margin of the terminal sieve-plate in many Euplectellidse. These difi"er from the 

 above chiefly in this, that their four transverse rays are not abortive, but remain more or 

 less long, so that the spicules are not diacts but hexacts. At the oscular aperture of 

 Tsegeria a peculiar form occurs in which the distal rays are specially long and peculiarly 

 bent (PL VIL); 



Dermalia. 



As to the spicules of the dermal skeleton, which all deserve the title dermalia, some 

 belong wholly or at least specially to the outer bounding skin, and have their axial cross 

 and transverse rays within the latter, while others lie for the most part under the 

 dermal membrane, with a more or less specially developed proximal ray extending for a 

 variable distance towards the interior, and with the axial cross and transverse rays 

 either lying immediately below the inner side of the dermal membrane, or even some- 

 what removed towards the interior. Although these tw^o forms of dermalia are not by 

 any means sharply separable from one another, it may be convenient to distinguish 

 them by the special designations autodermalia and hypodermalia, especially where they 

 occur close to one another. 



As examples of autodermalia, which are exclusively confined to the dermal 

 membrane, I may cite the dermal tetracts of Lanuginella pupa (PL LIIL figs. 4, 5) and 



1 



