FROM THE INFERIOR OOLITE. 549 



an irregular network of fibres, from 0*005 to 0-01 inch in diameter ; 

 the fibres become flattened and thickened in the plane of the gastral 

 surface, and thus give a sharp definition to the central cavity; a 

 thin epitheca covers the sponge externally. No other signs of a 

 canal-system besides the central cavity are present. 



Log. Hampton Down. 



Hor. Great Oolite. 



Liitxorea ptgmjea, sp. nov. (Plate XXI. figs. 29 & 30.) 



Sponge consisting of small teat-like individuals, 0*18 to 0*23 inch 

 in diameter at the base, 0'25 inch high, growing from a common 

 base, which is overgrown below by a thick concentrically wrinkled 

 epitheca ; attached by a very short thick peduncle. At the summit 

 of each mamillary individual is a small circular oscule, 0-08 inch 

 in diameter, from which a cylindrical tube descends vertically for a 

 considerable distance ; no radiate canals are visible on the exterior. 

 Skeleton an irregular network of small fibres, 0-0025 to 0-005 inch 

 in diameter, and thus much finer than those of the preceding species ; 

 the meshes of the network are also correspondingly smaller. 



As some of the characters of this species remain undetermined, 

 its generic position must be regarded as provisional. 



Log. Hampton Down. 



Hor. Great Oolite. 



Thamnoxema, gen. nov. 



Sponge globular, without a central cavity. Skeleton a net- 

 work of fibres, having, as seen from the exterior, the following 

 disposition : — from a common origin in the centre of the base 

 three fibres radiate in three directions, making equal angles with 

 each other; each soon bifurcates, and the fibres resulting break 

 up at their distal ends into an irregular network of smaller fibres, 

 which extends meridionally up to the summit, uniting with the 

 adjoining fibres along its whole length. The fibre over the base 

 curiously simulates the form of one of the bifurcate tern ate spicules 

 of the TetractinellidEe. The summit is occupied by a looser network 

 (i.e. with larger meshes) than the sides. The sides are ridged and 

 furrowed meridionally, the furrows looking like exposed radiate 

 canals ; the open meshes of the summit have the appearance of a 

 number of small oscules. 



The distinction of this genus depends on the curious arrangement 

 of the fibre at the base, and its subsequent division to form a reti- 

 culate fibre, characters which, so far as I am aware, are unique 

 among the Spongiae. 



Thamitonema pisieorme, sp. nov. (Plate XXI. fig. 28.) 



Sponge globular, flattened at the summit, free, I inch high and 



A inch broad. Primary fibre of the base 0*014 inch in diameter, 



secondary fibre 0*007 to 0-01 inch; fibres of lateral network 0-003 



to 0*007 inch in diameter. 

 Log. Hampton Down. 

 Hor. Great Oolite. 



