12 F. CJtapman : 



in diameter.^ In its vertical height, from the base of the 

 stalk to the level of the rim, this sponge probably measured 

 above 5 cm. 



iStruoture of the Median Layer. — What little remains of the 

 vertical pillars resembles the same structure seen in the 

 organism preserved in the limestone matrix, and is shown by 

 the impressions of the extremities of the pillars taken off the 

 fossils by wax squeezes. The pillars are hollow and constricted 

 near the junction wdth the outer sjMcular layers. 



Structure of the Upper and Lower Layers of the Body Wall. — 

 The superficial aspect of the (.t)ueensland specimens varies ac- 

 cording to the particular part of the external layer exposed. 

 Both the summit plates and the underlying spicules in contact 

 with them are clearly seen, and there seems evidence of more 

 than one spicule layer underlying the rhombic plates of the 

 inner or upper surface. So far as can be seen in these speci- 

 mens, the vertical pillars, constricted near their summits on the 

 inner side of the body wall (endorhin), suddenly expand and give 

 rise to a four-rayed spicular body similar to that shown in the 

 structural diagram of Receptaculites by Billings''* (Plate IV., 

 Fig. 5). 



As previously stated, there is often an intermediate spicule 

 layer between the expanded ends of the pillars and the outer 

 layer of summit plates with their spicular mesh. In this inter- 

 mediate layer there is ai parallel series of fusiform spicules, one 

 end of each spicule being capitate and giving rise to a slender 

 axis turning off at an angle between 90 deg. and 100 deg., and 

 w^hich immediately passes beneath the fusiform spioule-layer. 

 Some approach to this kind of structure is seen in the spicular 

 mesh of Sphaerospongia, an allied genus with hexagonal summit 

 plates, from the Devonian of Devonshire, Germany and Russia." 



The external layer is less often seen in our specimens, but 

 when recognisable it shows the sub-rectangular character of the 

 summit plates of the "ectorhin." 



1 The largest specimens figured by Etheridge and Dun from New South Wales also con- 

 ifinn this measurement. 



2 Geol. Surv. Canada, Palaeozoic Fossils, vol. i., 1865, p. 382. 



3 See Hinde, Pal. Soc. Mon., \ol. xl., 1886 (1887). Brit. Foss. Sponges, pt. i., pi. iv., 

 fig. 20. 



