62 SILICEOUS SPONGES. 



Several vertical canals, 1*8 mm. wide, op:^n at the summit; the lateral surfaces 

 have scattered apertures of canals, "8 mm. in width. 



The body-spicules have prominent junction-nodes and relatively long smooth arms. 

 The dermal layer is composed of the horizontally-expanded heads of large trifid 

 spicules, some of which are 1 mm. in extension. There are traces of minute spicular 

 bodies between the arms of the larger spicules of the dermal layer, but their form 

 has been lost. 



The specimens only occur in the interior of flints ; they retain the outer form and 

 the spicules of the dermal layer, as well as of the body-skeleton immediately beneath ; 

 but the interior is a mass of porous silica in which even the canals are destroyed. 



This species differs from G. acaule, Zittel, principally in its rounded summit and 

 the absence of a cup. 



Distribution. Upper Chalk : Croydon, Guildford, Surrey. 



Genus TRACHYSYCON, Zittel, 1878. 



Teachtstcon nodosum, Hinde, n. sp. (Plate XII. figs. 3, 3 a, 5 b.) 



Body of sponge massive, barrel-shaped, with a truncated summit bounded by a 

 subangular margin ; the stem has not been preserved. The lateral surfaces are 

 covered with rounded or obtuse elevations disposed irregularly. The only specimen 

 is 155 mm. in height and 117 mm. in width. 



The cloaca is subcylindrical, somewhat wider below than at its aperture ; it extends 

 rather more than one third the length of the body ; in the present specimen it is 

 55 mm. in length by 31 in width. The interior surface of the cloaca is thickly 

 covered with the canal-apertures, which are apparently disposed in vertical series. 

 These apertures are 1-75 mm. in width. The canals from the basal portion of the 

 sponge-body run nearly straight to the cloaca ; those from the lateral portion follow 

 a winding course ; whilst the canals springing from near the upper margin of the 

 sponge are bent downwards, following the contour of the summit so as to open into 

 the upper portion of the cloaca. There is also a series of numerous fine canals, 

 •75 mm. in width, extending from the exterior surface in a curved direction towards 

 the centre of the sponge. 



The body-spicules are moderately large ; their arms, -3 mm. in length, are smooth 

 or sometimes tuberculated ; they are much branched, and the junction-nodules are 

 swollen. No surface-spicules have been preserved. 



The single example of this species in the collection is filled with translucent chert, 

 in which the body-spicules are fairly well preserved ; the exterior surface is rough, 

 and shows no structure. 



Distribution. Upper Green Sand : Warminster, 



