THAMNOSPONGIA. 79 



Chalk, which diflfers from the Upper-Chalk specimens in the characters of the 

 interior canals. 



Thamnospongia glabra, Hinde, n. sp. (Plate XVII. figs. 5, 5 «, 5 h, 5 c.) 



Sponge growing in bushy masses, consisting of cylindrical upright or bent stems, 

 which give off irregularly, at an open angle, short curved branches with conical Or 

 blunted extremities. A single mass attains a height of 160 mm. ; the stems are from 

 8 to 11 mm. in thickness; the lateral branches are somewhat less. The surface of the 

 sponge in many specimens is extremely smooth, but in others, where the dermal 

 layer is absent, it is rough. 



The canal-structure in all the specimens is very imperfectly preserved, and I am 

 unable to affirm the presence of more than a single longitudinal canal, which is 

 faintly apparent in the centre of some of the stems, and is about 1'75 mm. in width ; 

 it is possible, however, that other canals would be seen in well-preserved specimens. 

 The terminals of most of the branches do not exhibit canal-apertures. 



The interior skeletal mesh is formed of very minute tuberculated spicules, with 

 arms or rays about -16 mm. in length. The dermal layer is smooth and compact ; 

 the heads of the largest of the trifid spicules are -3 mm. in width ; between the larger 

 forms are very numerous small ones. As a rule, the larger spicules have fallen off 

 the surface of the dermal layer, leaving, however, distinct impressions of their form, 

 and of the shaft of the spicule, in the centre of each. In two small branches of a 

 sponge, apparently belonging to this species, which Mr. H. J. Carter, F.E.S., has 

 presented to the Museum, the smooth dermal layer exhibits in places minute groups 

 of circular pores. There are about ten of these pores in a group, which is only 

 •3 mm. across ; the groups are once or twice their own width apart. The pores are 

 close together, and their margins are smooth and well defined. 



This species differs from the next in its mode of growth and in the characters of 

 the dermal layer, the spicules of which are much smaller than in T. clavellata. It 

 appears to be not uncommon in the Upper-Chalk flints of the south-west of 

 England. 



Distribution. Upper Chalk : Woodford, Beckhampton, Wiltshire ; near Budleigh 

 Salterton, Devonshire, in superficial detritus {Mr. II. J. Carter). 



Thamnospongia clavellata, Benett, sp. (Plate XVIII. figs. 2, 2 a, 2 b.) 



1831. Polypothecia clavellata, Benett^ Cat. Org. Rem. Wilts, t. 12. 



1854. Spongites clavellatus, Mantell, Medals of Creation, vol. i. p. 224, f. 2. 



Sponge generally consisting of a single straight or slightly sinuous stem, which 

 gives off', mostly at right angles, short stumpy branches or spur-like processes, either 

 blunted or rarely bulbous at their extremities. In some cases the branches extend 

 to the adjoining stems and coalesce with them ; but, as a rule, the stems are single. 



