SPOEADOSCINIA. — SESTEOCLADIA. 117 



somewhat greater thickness, though I do not think that in this instance it has been 

 much compressed. The only specimen, which is destitute of the lower portion of 

 the funnel, measures 170 mm. in height by 168 in width at the summit. 



The outer surface of the wall is pierced with irregularly disposed, transversely 

 elliptical or ovate apertures, from 1 to 1'8 mm. in length and about "6 mm. in width. 

 These apertures are only separated by slender wall-fibres, about '7 mm. in width. 

 The inner surface has circular or slightly ovate apertures, 1"6 mm. wide, and about 

 the same distance apart, regularly disposed in quincunx. 



Only a portion of the wall has been preserved, and the spicular structure is either 

 in the condition of hollow moulds, or these are partially filled with peroxide of iron. 

 The interior mesh appears to be very irregular ; the distance between the octahedral 

 spicular nodes is "3 mm. The dermal layer appears to have been furnished with 

 stout spines, which projected from the surface and into the canals in the same 

 manner as represented by Zittel in S. micrommata*. 



The main diff'erence between this species and S. Decheni, Goldf., independent of 

 its much larger size, consists in the difierent form and arrangement of the apertures 

 of the outer surface of the wall. 



Distribution. Lower Chalk : South of England, 



Genus SESTEOCLADIA, Hinde, n. g. 



Sponge ramose, consisting of cylindrical or compressed bifurcating branches. The 

 branches are hollow tubes, open at their summits. The outer surface of the sponge 

 is formed by anastomosing ridges or folds with ovate interspaces. The interior 

 surface is concealed by the matrix, but, judging from vertical and transverse sections, 

 it appears to be penetrated by apertures similar to those of the outer surface. The 

 spicular mesh of the interior of the wall is irregular, the spicular nodes are octa- 

 hedral. The outer surface of the ridges or folds of the wall apparently possessed a 

 dermal layer, but its minute structure is not discernible. 



This genus is distinguished from all others of the family of the Ventriculitidse by 

 its dendritic mode of growth. 



Sesteocladia fuecatqs, Hinde, n. sp. (Plate XXVII. figs. 1, 1 «, 1 1.) 

 Sponge apparently growing from a simple stem, which gives ofi" divergent branches 

 at irregular intervals. The branches have a generally upright direction of growth ; 

 they are from 15 to 28 mm. in diameter, usually cylindrical, but near the points of 

 bifurcation they are frequently compressed and expanded. The single example, 

 which is imperfect, is 155 mm. in height, and the lateral extension is 140 mm. The 

 thickness of the wall is 3 mm. 



* Neues Jahrbuch, 1877, Taf. 3. fig. ba. 



