778 REPORT—1899. 
skeletal canals in the basal region of the sponge, these being left empty, or with 
only a thin layer of tissue on their walls. 
Zoological Position.—That the animal under consideration belongs to the 
Porifera seems clear from the presence in the soft tissues of numerous chambers 
provided with flagella and communicating with a system of canals which ulti- 
mately open to the exterior by pores. The soft tissues are, moreover, supported 
by a skeleton composed of elements which are secreted by cells of the jelly. 
On the other hand, that it is not a Celenterate is shown by the absence of 
polyps, mesenteries, and thread-cells. 
But admitting that Astrosclera is a Sponge, there are many features which 
separate it from the living members of this group. Among these may be men- 
tioned :— 
(a) The shape of the skeletal elements. They are polyhedra, which begin as 
spheres, and may pass through a spheraster stage. 
(6) Their union to form a rigid skeleton to the exclusion of the soft parts. In 
Petrostroma of Déderlein the supporting skeleton is also formed of fused calcareous 
spicules, but these are modified quadriradiates. 
(c) The mode of growth by the addition of new skeletal elements at the upper 
surface, and without interstitial growth. 
(d) The limitation of the pores to the upper surface. Tewtoriwm (Vosmaer), 
a siliceous sponge classed with the Polymastide, presents a similar limitation. 
(e) The absence of large gastral spaces. 
(7) The small size of the ciliated chambers. They do not exceed 18u by 11p, 
while the smallest size given by Heckel for the Lewcones (whose ciliated chambers 
are smaller than those of other Calcarea) is 60% by 40u. Among the non-Calcarea 
42u is the smallest diameter given for the ciliated chambers. 
(g) The character of the cells bearing the flagella. They appear not to be 
collar-cells of the usual type, but more or less amosboid, and without a collar, the 
body of the cell gradually tapering into the flagellum. 
From the Calearea it differs also in the following features :— 
(a) The flagellate cells are limited to about half the interior of the ciliated 
chambers, 
(6) There appears to be a long and complicated canal system both on the 
afferent and efferent sides of the ciliated chambers. 
(c) The mineral constituent of the skeleton is aragonite and not calcite. 
While Astrosclera is very distinct. from any of the families of living sponges, 
its resemblance to certain members of the group of fossil sponges Pharetrones is 
very striking. These are found in strata ranging from the Devonian to the 
Cretaceous periods. 
The feature characteristic of many members of this group (though authorities 
are by no means agreed either on its essential characters or limits) is that the 
skeletal elements are united together into dense trabecule or ‘fibres,’ as they are 
technically called, between which a branched canal-work is often present, leading 
into a central gastral cavity. The latter, however, may be so shallow as almost 
to cease to exist. A cortical layer, which has been thought to be imperforate, 
often clothes the outer surface of the cylindrical members of this group, and in that 
case the pores leading to the interior would be limited to the upper part of the 
sponge. Insome cases radiating grooves are present on the upper surface con- 
verging towards the mouth of the gastral cavity, the initial stage of the branched - 
canals of the interior. 
If we suppose the trabeculz of the skeleton of one of the simple forms to 
increase in thickness, and the gastral cavity to become wholly obliterated (as is 
very nearly the case in Stedlispongia), we have a form agreeing with <Astrosclera 
in the larger features of the anatomy of the skeleton. 
On turning our attention, however, to the elements of which the fibres of the 
skeleton are formed, we find that in the Phwretrones in which the structure is most 
