R. W. H. ROW—REPORT ON THE SPONGES : CALCAREA. 191 
these two families, and the obvious identity of their chiactines, all indicating 
that the Staurorrhaphidee are directly derived from the Chiphoride. 
It must thus, in any case, be assumed that a dermal cortex has appeared 
independently in two different groups; and the occurrence of a third inde- 
pendent appearance of this structure, as shown above, for the Grantillide, 
presents no serious difficulty. This, doubtless, took place very early indeed 
in the history of the Grantillidee, very soon after the first appearance of tbe 
subgastral prochiact, and while the skeletogenous cells were still plastic and 
easily influenced by varying conditions. Previously to the appearance of the 
dermal cortex, the only support for the chamber-layer consisted in a system 
of small spicules in the walls of the chamber, completely separate from the 
skeleton of the adjacent chambers, to which its only skeletal union was through 
the mediation of the gastral cortex. Immediately upon the appearance of a 
dermal cortex, however, many new opportunities arise for strengthening the 
skeletal framework. 
In many cases this strengthening consists in the development of the cortex 
to enormous proportions, with a special skeleton consisting of either large 
oxea or triradiates tangentially arranged, as in Ute in the Grantide and 
Grantiopsis in the Staurorrhaphide. Among the Grantillide the same result 
has been obtained in an entirely different way, namely, by the development 
of subdermal spicules with one ray pointing gastralwards. Two entirely 
different types of spicule have thus appeared simultaneously, the prochiact 
and the quadriradiate. The presence of a complete series of stages between 
the prochiact and the secondary sagittal triradiate seems to me to be con- 
clusive proof that these two forms are not separate developments, but that one 
of them is directly derived from the other. 
An imaginary primitive or Prograntillid type might be diagnosed as 
follows:—-“ Calearea with a distinct dermal cortex covering the chamber-layer. 
Canal-system syconoid, with an articulate tubar skeleton supplemented by 
subgastral prochiacts and subdermal prochiacts, sagittal triradiates and quadri- 
radiates.” This may be considered to have been the ancestral type from which 
the living Grantillidee, the Heteropide, and the Amphoriscidz have all been 
derived. The Grantillide, at any rate in so far as they are represented by 
the genus here under consideration, (rrantilla, have reached their present form 
by the retention of all the types of subdermal spicule, and the loss of the 
primitive articulate tubar skeléton. The Heteropidze, on the other hand, 
have specialized in the subdermal sagittal triradiates, and no longer possess 
either subdermal prochiacts or quadriradiates ; while the Amphoriscide have 
lost the whole of the prochiact-sagittal triradiate series, and have retained 
the subdermal quadriradiates only. 
Since arriving, in conjunction with Professor Dendy, at the above con- 
clusions with regard to the phylogeny of the Heterocceia, I have seen a paper 
by Geoffrey Smith, on the Anaspidacea (17), in which he develops the same 
