188 CALCAEEOUS SPONGES. 



Sestrostomella rugosa, Hinde. (Plate XXXV. figs. 4, 4 «, 4 h-d.) 



1882. Sestrostomella rugosa, Ilinde, Ann. & Mag. Nat. Hist. ser. 5, vol. x. p. 198, t. 10. 

 f. 6, and t. 12. f. 1-15. 



Sponges gvowiug in upright bushy masses, consisting of subconical and subcylin- 

 drical individuals, about 12 mm. in thickness, united at their bases and occasionally 

 laterally, but free at their summits. The type specimen is 68 mm. in height and 

 76 mm. in breadth. The lower portion of the sponge is enveloped in a compact 

 rugose dermal membrane. The surface exhibits an irregular open network of coarse 

 fibres. Where a cloacal aperture is present, it is about 2 mm. in width, but the 

 summits of some individuals do not show any distinct aperture ; in nearly all, open 

 canals extend from the summit down the sides of the sponge. 



The fibres, as seen in a transparent transverse section, vary from '2 to -41 mm. in 

 width. They are composed of relatively large, axial or subaxial, three- and four- 

 rayed spicules, the rays of which, in some cases, reach to '5 mm. in length and 

 •06 mm. in thickness. These central spicules are surrounded by small and minute 

 irregular three-rayed spicules, which present an appearance of wavy lines closely 

 following the contours of the fibre. These smaller spicules are so closely interwoven 

 together that it is difficult to determine their individual forms ; but amongst others 

 there is a very characteristic slender spicule, resembling in form a pitch-fork or 

 tuning fork. The basal ray or the handle is straight and tapering, whilst the paired 

 rays or tines of the fork are subparallel, and frequently one is slightly longer than 

 the other. The longest of these pitch-fork spicules which I have seen measures 

 altogether "o mm. 



Distrihiition. Cretaceous. Upper Green Sand I : Vaches Noires, near Havre. 



Sestrostomella clavata, Hinde. (Plate XXXV. figs. 5, 5 a.) 



1882. Sestrostomella clavata, Hinde, Ann. & Mag. Nat. Hist. ser. 5, vol. x. p. 201, t. 10. 

 f. 5, and t. 12. f. 16-25. 



Sponges growing in bushy masses, consisting of numerous cylindrical individuals, 

 from 8 to 10 mm. in diameter, radiating from a common centre. No pedicel is 

 present, but a small smooth place indicates the spot on which the sponge rested 

 during its growth. The summits are rounded; the cloacal aperture is about 2'5 mm. 

 in width ; in some cases only canal-apertures are present at the summit. Straight 

 open canals extend from the summit down the sides. 



The minute structure of the fibres of this species is essentially similar to that of 

 the preceding, but it differs in form, mode of growth, and the somewhat more slender 

 dimensions of the fibres. In one part of a thin transverse section the characters of 

 the exterior portion of the fibre are clearly exhibited, and it is seen to be made up 



