436 PROCEEDINGS OF SECTION C. 



skeleton. The outer wall may aptly be compared in structure, to 

 an inverted incandescent mantle containing another (the inner wall) 

 several sizes smaller, the two being united by fairly solid radiating 

 septa somewhat sparsely perforate. Perforate tabulae are almost 

 invariably present also. One important function of the skeleton 

 would, therefore, appear to be to allow extremely free communication 

 between the central cavity and the exterior. The central cavity of 

 the organism is apparently devoid of dissepimental tissue, in all the 

 specimens I have examined, to the bottom of the cup— which fact 

 seems to indicate a circulation of food and oxygen after the sponge 

 type ; probably from the outside, through the walls to the inside, and 

 out through the mouth of the cup. 



At first glance one might compare the family to various compound 

 Coelenterata, such as HaUjsites, where the corallites are united linearly 

 to form walls consisting of oval tubes. But it seems difficult to reconcile 

 each parallel-sided loculus (fig. 7), in the Cambrian family with the 

 calice of a polyp. Secondly, as shown in fig. 6, the free edges of the 

 rims of the central cavity seem to show a fusion of outer and inner 

 walls, and not the open, growing, portion of the coralites, as one would 

 expect in an Anthozoan. 



The microstructure of the organisms, where every pore is preserved 

 apparently in the original lime, shows that the septa are built up of 

 minute granules. No sign of true sponge spicules is so far apparent 

 in the septa, though such spicules have been detected at some distance 

 from the Archeocyathinse. The dense lamellar uniform character of 

 the perforate septa resembles much more closely the septa of a madre- 

 porarian than any similar structure in a sponge. The regular growth 

 and strict parallelism of the septa, tabulae, and walls respectively is 

 quite antagonistic to a close relationship with the Porifera of Palaeozoic 

 age. 



Yet the irregularity of the shape merging from a Pharetrone type 

 to a flabellate Clathrina type is poriferate in character. The presence 

 of anchoring rhizoids is suggestive, as such are very usual in many 

 sponges. The budding of small individuals from the walls of the large 

 ones is common to both coral and sponge, though the Archaeocyathinae 

 habit resembles the latter more closely in this respect. 



Serial sections through certain of the Sellick's Hill specimens show 

 that in some genera the cavity of the calice is wider in the middle, and 

 contracts to a small aperture at the upper end. This, also, is contrary 

 to coral morphology. 



From a consideration of the growth habit of the flabellate types 

 (figs. 6 and 7), i.e., with the rhizoids normal to the perforate wall, it 

 would appear evident that the nutrition zone was represented by the 

 upper perforated wall, and not by the free rim, as analogy with Halysites 

 and other Anthozoa would require. 



Further study of the small nepionic forms will undoubtedly assist 

 greatly in determining the classification. They would appear to arise 

 from a more or less globular cell, around which other cells are built, the 



