190 BRITISH JURASSIC SPONGES. 
In the Middle Lias the only siliceous sponge yet known is a solitary specimen 
of the Lithistid genus Platychonia (Pl. XII, figs. 4, 4a) discovered by the 
Rey. P. B. Brodie in the Marlstone at Ilminster. In some decayed rusty beds of 
the sand rock at King’s Sutton, in Northamptonshire, Mr. KE. A. Walford found 
the minute specimens of Leucandra Walfordi, Hinde (Pl. XIX, figs. 8—8 c), the 
earliest known fossil Calcisponges in this country, with the exception of some 
detached spicules occurring in Carboniferous strata, and further distinguished as 
the sole fossil representatives of the family of Leucones, very numerous in 
existing seas. 
From the Upper Lias no sponges are as yet known in our area, but in the 
Inferior Oolite they occur in great abundance, and they form an important, 
though hitherto scarcely recognised, element of the fauna of this series. 
In the lower division of the Inferior Oolite in the Cotteswold area, included in 
the zone of Ammonites Murchisone, an interesting group,, inclusively of Calci- 
sponges, has been brought to light through the researches of Mr. R. F. Tomes, 
Mr. F. Longe, and others. They mostly belong to Peronidella tenuis, Hinde; 
Corynella punctata, Hinde; Lymnorella mamillosa, Lamx.; L. inclusa, Hinde ; 
I. vamosa, Hinde; and Blastinia costata, Goldfuss, and they occur more 
particularly in the Pea-grit series and in the Oolite-Marl of Crickley Hill, 
Cleve Hill, and Ravensgate Hill, near Cheltenham, and at Birdlip Hill, near 
Gloucester. Lately, Mr. E. Wethered has pointed out the occurrence of several 
of these species in a definite sponge-bed in the Pea-grit series, exposed in a railway 
cutting at Andoversford, near Cheltenham (‘ Quart. Journ. Geol. Soc.,’ vol. xlvu, 
1891, p. 553). In this lower division of the Inferior Oolite, sponges belonging to 
the genus Lymnorella, Lamx., are by far the most numerous; they frequently 
occur in nodular masses, partly incrusted by Polyzoa. 
In the higher division of the Inferior Oolite, belonging to the zone of 
Ammonites Parkinsoni, British Jurassic sponges reach their greatest development. 
They are best shown in the grey limestone strata which cap the cliff at Burton 
Bradstock, near Bridport, Dorsetshire. Large masses of this limestone have in 
places fallen to the beach and have become weathered, and their upper surfaces 
show that the rock is mainly composed of masses of sponges growing attached to 
each other, apparently still in their natural position. The greater number are 
evidently siliceous sponges, but though they retain their original forms fairly well, 
their canal structures are largely obliterated, and the silica of their spicular 
skeletons has been entirely replaced by carbonate of lime, and thus they offer 
great difficulty in determining their character and relationships. The majority of 
the siliceous sponges in these beds are Hexactinellids, belonging to the genera, 
Tremadictyon, Zittel; Calathiscus, Sollas; Oraticularia, Zittel; Verrucocelia, 
Ktallon; and Stauroderma, Zittel, but there are also several species of the 
