128 SILICEOUS SPONGES. 



regular manner as to leave quadrate or oblong interspaces like lattice-work. An 

 extremely delicate tissue, composed of much smaller and more slender spicules, 

 disposed without any regularity, fills the spaces formed by the regular framework 

 of the larger spicules, the whole forming an apparently compactly interwoven dermal 

 layer. 



The interior of the funnel formed by this dermal layer is occupied by anastomosing 

 meandriform laminae or thin walls of spicular tissue similar to those which characterize 

 the genus Plocoscyphia. The spicular tissue is of a very irregular character, and the 

 spicular nodes are solid. 



In this genus the features which distinguish the families of the Staurodermidse and 

 the MeandrospongidsB appear to be present : the large cross-shaped spicules of the 

 dermal layer are essentially similar to those of the former family, and the disposition 

 of the internal spicular mesh is the same as in the latter family. 



There is a certain resemblance between the markings on the outer surface of the 

 small conical sponges of the genus Eubrochiis, Sollas, and the present genus ; but so 

 little is known both of the exterior and interior structure of Euhrochus, owing to the 

 imperfect preservation of the specimens, that it is impossible to institute a comparison 

 between these genera. The spicular structure both of the dermal layer and of the 

 interior wall of Cincliderma is, however, altogether different from the magnified 

 representation of these structures in Eubrochus as given by Sollas*. 



Cincliderma quadbatum, Hinde, n. sp. (Plate XXVIII. figs. 1, 1 «, 1 ^, 1 c, Id.) 



The broken-up fragments of this species appear to have formed part of a funnel- 

 shaped specimen, 46 mm. in width at its summit. The dermal layer is extremely 

 thin, and formed by a single layer of spicules ; the rectangular spaces, bounded by 

 the larger spicules, vary in size between "75 mm. and 1'8 mm. The rays of the large 

 spicules overlap each other, and they all possess a fifth ray extending into the wall. 

 In a few instances the smaller spicules of the interspaces of the lattice-work are 

 disposed so as to divide them further into smaller quadrate spaces ; but, as a general 

 rule, these smaller spicules are disposed indiscriminately over each other. The 

 anastomosing wall-plaits of the interior of the sponge are about 1'8 mm. in thick- 

 ness ; the spicules of the mesh are relatively large, and very irregular in form. 



The sponge is preserved in chalk ; and the siliceous spicular structure has been 

 either replaced by iron peroxide or it has been dissolved, leaving empty moulds in 

 the chalk. 



Bistrihution. Upper Chalk : South of England [coU. T. Smith). 



* Geological Magazine, Dec. 2, vol. iii. pi. 14. figs. 3, 4, 5. 



