PLOCOSCYPHIA. 137 



Plocosctphia labteinthica, Mant. sp. (Plate XXIX. fig. 5.) 

 1822. Spongus labyrinthicus, Mant. Foss. of the South Downs, p. 165, t. 15. f. 7. 



Sponges irregular in form, composed of anastomosing walls arranged in open 

 convolutions. The walls are from 2-5 to 3 mm. in thickness ; their outer surfaces 

 are perforated by circular canal-apertures about -7 mm. in width. The distance 

 between the nodes of the interior mesh varies from 'So to '4 mm. 



The examples of this sponge are usually preserved in hemispherical nodules of 

 flint, which exhibit on their flattened upper surfaces sections of tlie convolute walls. 

 This species is distinguished from P. flexuosa by the greater thickness of the walls 

 and the more open character of the convolutions, whilst the size of the spicular mesh 

 appears to be similar. 



Distribution. Upper Chalk: Bridgwick; OSham, Kent {coll. Mantell). 



Plocoscyphia vagans, Hinde, n. sp. (Plate XXIX. figs. 6, 6 a.) 



Sponges irregular in form, with convoluted walls about 1'5 mm. in thickness. The 

 spicular mesh is composed of large spicules with lantern nodes ; the distance between 

 the nodes varies between -625 and -8 mm. 



The examples of this species are all preserved in chalk, and the spicular mesh is 

 now changed to iron peroxide or shown by empty moulds. The species is readily 

 distinguished from those previously described by the unusually large size of the 

 spicules of the interior mesh of the wall. 



Distribution. Upper Chalk : Maidstone, Kent, and other localities in the South of 

 England (coll. T. Smith). 



Plocosctphia foliacea, Toulm. Smith, sp. 

 1818. Brachiolites foUaceus, T. Smith, Ann. & Mag. Nat. Hist. vol. i. p. 361, t. 16. f. 1. 



Sponges club-shaped, usually curved in the lower portion, with a few small 

 divergent rootlets at the base, the summits rounded. The outer surface smooth, 

 with irregularly disposed rounded elevations and depressions. A fairly large example 

 measures 155 mm. in length, and 48 in width at the summit. 



The body of the sponge is composed of anastomosing walls from 1 mm. to 1-75 in 

 thickness, disposed in open convolutions. 



The examples of this species are preserved in chalk, and the spicular structure 

 is only indicated by markings in iron peroxide, in which the character of the mesh 

 has been obliterated. Its form and the features of the outer surface distinguish it 

 from other species of this genus. Toulmin Smith's figure of this form is partly a 

 restoration. 



Distribution. Upper Chalk : South of England {coll. T. Smith). 



