198 MARINE BIOLOGY OF THE SUDANESE RED SEA. 
The remarkable consistency with which, throughout these families, the 
primitive tubar spiculation is replaced by spicules which, though of various 
kinds, are in every case derived from cortical triradiates, seems to me to be 
very strong evidence in support of the true phylogenetic unity of the group. 
This view of the evolution of the more highly organized families of the 
Heteroccele Calcarea differs from that suggested by Dendy (2) only in 
the derivation of the Heteropidee and Amphoriscide, not directly from the 
Grantidee, but as an entirely separate line from Sycettid (2. e. non-corticate) 
ancestors. This modification has been rendered necessary by the undoubtedly 
primitive character of the prochiact, and the important part which it is con- 
sidered to have played in the evolution of the group. 
GRANTILLA QUADRIRADIATA, sp.n. (PI. 19. figs. 1, 2.) 
The sponge is represented by a fragment only (PI. 19. fig. 1), of a single 
sycon person, possessing neither osculum nor attachment, so that a full 
description of its external form is impossible. The specimen is cylindrical in 
form, and measures 12 mm. in length and 26 mm. in diameter at the widest 
part. 
The canal-system is typically syconoid, and the chambers do not appear 
to be at all branched (PI. 19. fig. 2). 
The skeleton arrangement of the chamber layer is of the inarticulate tubar 
type, composed of sagittal triradiates and prochiacts on both surfaces, and also 
of subdermal quadriradiates, and a few oxea. 
Dermal and gastral cortices are present, each containing tangentially 
arranged triradiates. 
Skeleton arrangement. (PI. 19. fig. 2.) 
A. Dermal cortex. 
The spiculation of the dermal cortex, which is fairly thick, consists entirely 
of triradiates (text-fig. 2, ¢). These are fairly large, typically quite regular, 
with their rays of equal length, though many of them show a slight dif- 
ferentiation of their angles into oral (the largest) and paired, in which case 
the basal ray is usually very slightly longer than the oral. All the rays are 
equal in thickness. They are arranged over the surface of the sponge entirely 
without regard to orientation, except that they are placed tangentially. 
B. Tubar skeleton (Text-fig. 2, a, 6, c, d). 
(i.) Quadriradiates (Text-fig. 2, c).— These are the only quadriradiates 
present in the sponge, and are large subdermal quadriradiates, whose facial 
rays are decidedly sagittal, the two oral rays being usually nearly in a straight 
line and the oral angle almost 180°. The apical ray is considerably the 
longest, frequently being nearly three times as long as the facial rays. It 
is quite straight and of the same diameter for most of its length, the 
diminution in thickness being confined to the distal third of its length. 
