R. W. H. ROW—REPORT ON THE SPONGES: CALCAREA. 189' 
Jenkin’s chiactines, save that they possess an apical ray, are very similar 
to prochiacts. The basal ray lies in the wall of the chamber, “ viewed along 
the axis of the basal ray, the paired rays are seen to be folded to one side ” 
(Jenkin). The apical ray of a quadradiate is, so far as we know from other 
cases, both developmentally and phylogenetically a structure of much later 
origin than the facial rays. Jenkin, moreover, states that in Streptoconus, 
whose canal-system is the most primitive of all the chiact-bearing sponges 
at present described, some of the chiactines lack the apical ray. (They are 
therefore prochiacts.) 
The extreme similarity between the chiactine and the prochiact above 
described is thus evident, the only difference, save as regards the apical ray, 
being that the oral angle of the chiactine, to judge by Jenkin’s figures, is 
greater than that of the prochiact. The presence of a complete series in 
Grantilla, however, in which spicules are found whose original oral angle 
may be widened out to anything between 90° (in some prochiacts) and 180° 
(in the secondary sagittal triradiate), is evidence that this difference is of 
very slight significance ; and if, as I shall hope to demonstrate hereinafter, 
the prochiact is primitive, and the others, in which the primitive oral angle 
is larger, are more modified, then the width of the primitive oral angle of 
the chiactine would be clearly accounted for as a similar development of the 
primitive type towards a uniplanar spicule. The chiactine may therefore be 
looked upon as a direct development of the prochiact by the addition of an 
apical ray. 
Both the species of Grantilla possess prochiacts both in the subdermal and 
subgastral layers, and these spicules form a very large proportion of the 
tubar skeleton in each case. There are present, however, subgastral and 
subdermal sagittal triradiates, and, as above stated, intermediate forms are 
common. Further, in one of the species here described, Grantilla quadri- 
radiata, there also occur subdermal quadriradiates, with the apical ray pointing 
gastralwards. 
Thus these sponges unite in themselves the characteristic features of the 
spiculation of three groups, the Amphoriscid:e, the Heteropide, and the two 
chiactine-bearing families, the Chiphoridz and the Staurorrhaphidee. 
The most primitive sponge in which chiactine (and prochiact) spicules occur 
is Streptoconus, which, save for the presence of these spicules, would be placed 
in the genus Sycetta, the canal-systems of the two sponges being absolutely 
similar. The occurrence in so primitive a type of sponge of this spicule 
indicates its very great phyletic antiquity, showing in fact that the prochiact 
must have originated previous to the development of a dermal cortex. It is 
at this point that I differentiate the Grantillid line of descent from that of 
the Sycettidee—Grantide, including in the former line all those families 
which either still possess, or presumably have had in the history of their 
evolution, prochiact spicules. (See phylogenetic tree on p. 192.) 
Of these, the two families of chiactine-bearing sponges, the Chiphoride and 
