474 ASTROSCLERA WILLEYANA, THE TYPE OF A NEW FAMILY OF "SPONGES. 



exterior are limited to the upper part of the sponge. In some cases radiating grooves 

 are present on the upper surface, converging towards the mouth of the gastral cavity, 

 or towards the group of large pores which represents it, the initial stage of radiating 

 tributary canals of the interior. 



In the genus Stellispongia the gastral cavity may, as above noted, be absent 

 altogether, and a single group of large pores and radiating grooves may occupy the 

 centre of the upper surface of the sponge. In other cases, and even as it appears 

 within the limits uf the same species, the number of these groups of pores may be 

 multiplied. 



Among a number of specimens of Stellispongia vanabilis which I obtained from 

 Triassic deposits in the neighbourhood of St Cassian, in the Tyrol, and which have 

 been kindly named for me b}' Dr Hinde, there are specimens, referred to the variety 

 c of that species, expanding rapidly from a short pedicellate base, clothed on the 

 outer surface with a wrinkled cortical layer, and presenting in the middle of the upper 

 surface a shallow depression whose sides are marked by radiating gi-ooves, the first stage, 

 as we have seen of the tributary canals of the interior. In another example of the 

 species the rounded upper surface presents numbers of these systems of large pores 

 and radiating grooves, in some cases in depressions, in others flush with the general 

 surface. 



The resemblances between the surface of the latter specimen and that of the bosses 

 of the Funafuti specimen of Astrosclera, and between the general habit of growth of the 

 former specimen and the earlier formed part of the Funafuti specimen are certainly 

 very remarkable. 



On turning our attention, however, to the elements of which the skeleton is 

 composed we find a marked difference. In those Pliaretrones in which their characters 

 have been determined they are tri-radiate or quadri-radiate spicules, often haviuo- the 

 rays bent or reduced to allow of their being packed together to form the solid 

 trabeculae, but still distinctly referable to these types. They are well seen in the 

 Warminster specimens described and figured by Dr Hinde', who succeeded in obtaining 

 isolated spicules. The characters of the skeletal elements are however often found to 

 have been obliterated to a greater or less extent in the process of fossilization and 

 all traces even of the existence of spicules may be lost. 



In sections of the specimens of Stellispongia above mentioned the skeleton is seen 

 to be composed of bodies round in transverse section, but elongated in longitudinal 

 with a length often eight times the breadth, and with no definite structure discernible 

 in their interior. The appearance agi-ees with that figured by Steinmann for this 

 genus-. The outlines of the elements which make up the trabeculae are blurred, owing 

 apparently to commencing recrystallization, so that it is not easy to decide on their 

 original shape. Rauff^ asserts that tri-radiate spicules are to be recognised in some 

 specimens of Stellispungia from the Trias, and in my sections the elements often present 



' "Notes on Fossil Calcispongiae," loc. cit. 



' Cp. Steinmann's figure, " Pharetronen-Studien," Neiies Jahrbiich j. ilineralogie, &c. 1882, Bd. 2, PI. ix. 

 Figure 2. 



^ Palaeos-pongiologie, Th. 1. PalaeontO(iriqihica, Vol. xl. p. 99. 



