INTRODUCTION. 191 
Lithistid genera Platychonia, Zittel, and Leiodorella, Zittel, as well as a few 
Calcisponges belonging to the genus Peronidella, Zittel. 
At Shipton Gorge, not far from Burton Bradstock, in a quarry of the Inferior 
Oolite Limestone, on the same Parkinsoni-zone, Mr. H. A. Walford! discovered a 
thin sponge-bed containing an extraordinary number of small sponges associated 
with numerous species of Polyzoa. In contrast to the sponge-bed at the Burton 
Bradstock Cliff, which mostly consists of siliceous sponges, the Shipton Gorge bed 
is nearly entirely of Calcisponges belonging to the genera Perowidella, Zittel ; 
Holcospongia, Hinde; Lymnorella, Lamx.; Oculospongia, Fromentel; and Hudea, 
Lamx.; and the specimens are mostly of small dimensions. Only a few broken-up 
fragments of siliceous sponges are present in the same bed with the Calcisponges, 
and in these the siliceous structure has been entirely replaced by calcite, whilst 
the Calcisponges are hardly at all altered in their mineral composition, thus 
showing that, under similar conditions, siliceous sponges have much less capacity 
for resisting the destructive effects of fossilisation than Calcisponges. In com- 
parison with the difference of habitat in existing Hexactinellids and Calcisponges, 
it is interesting to note the joint existence of members of these groups in the 
same beds of the Inferior Oolite at this place. In some cases small Calcisponges 
still remain attached to the surface of Hexactinellids on which they have grown ; 
whilst in others the basal dermal surfaces of Calcisponges retain the imprint of 
the cruciform, dermal spicules of sponges belonging to the genus Stawroderma, 
Zittel, which formerly served them as a basis of growth. 
Beyond these two Dorsetshire localities there are but few others in the south- 
west of England which have yielded sponges in the upper beds of the Inferior 
Oolite. At Dundry Hill, near Bristol, the rare Lithistid, Melonella ovata, Sollas, 
sp., has been met with in the zone of Am. Humphresianus, and at Bradford Abbas, 
Dorset, a few specimens of Peronidella and Holcospongia. 
Passing upwards to the Great Oolite series it is significant that only Calci- 
sponges have as yet been found in these rocks in the British area. Members of 
this group are, however, by no means rare, and a very fine collection from the 
Great Oolite at Hampton Cliffs, near Bath, made by the late Mr. W. Walton, 
and presented by him to the Woodwardian Museum at Cambridge, has mainly 
served for the descriptions and figures given below. They are comprised in the 
following genera: Peronidella, Husiphonella, Corynella, Holcospongia, Lymnorella, 
Hlasmostoma, and Diaplectia. In the Forest Marble at Winsley, near Bath, in the 
Bradford Clay at Bradford-on-Avon, Wiltshire, and in the Cornbrash at Langton 
Herring, near Weymouth, a few Calcisponges also occur; those from the last- 
named places retain their spicular structure very perfectly. 
Some beds in the well-boring at Richmond, Surrey, at 1205 feet beneath the 
1 «Quart. Journ. Geol. Soc.,’ vol. xlv, 1889, p. 561. 
