28 — 



whilst the larger attain dimensions of 5,5 mm. in length by 

 0,135 mm. in width. Occasionally spicules of still larger di- 

 mensions are present; one of these, though incomplete at 

 one end, measured 9,2 mm. long by 0,214 mm. wide; a frag- 

 ment of another was 0,35 mm. in diameter. 



There are also straight and curved spicules (figs. 8, 9) 

 facsimiles of the larger spicules as regards their form but 

 very much smaller. The straight forms of these small exam- 

 ples average 1,35 mm, long by 0,022 mm. wide, whilst the 

 curved, shorter and proportionally stouter, average 0,585 mm. 

 in length by 0,067 ™ni. in width. These curved spicules are 

 abruptly pointed at both ends and very constant in form and 

 size. Both the larger and smaller forms are abundant in the 

 flint meal. 



Simple acerate spicules are common to so many different 

 forms of -sponges that it is impossible to determine the rela- 

 tions of detached spicules with certainty, but, judging from 

 the size of those in this deposit, they appear to me to cor- 

 respond rather with acerates which in existing sponges are 

 associated with the trifid spicules of Geodia and Stelletta 

 than with the acerates of monactinellid sponges. Similar 

 spicules are described by Mr. Carter from the Haldon Green 

 Sand and referred to Geodia- like sponges (An. Mag. Nat. 

 Hist. S. 4, Vol. 7, p. 129, PL 10, figs. 75, "jS); they are 

 present in the Upper Chalk of Coesfeld (Ueber Coelop. p. 36, 

 Taf IV, figs. 1—4) in the Chalk of the North of Ireland 

 (Wright : op cit. Plate II, fig. i ) and also in the Eocene sand 

 of Brussels (Rutot, op. cit. PI. Ill, figs, i — 4). 



Ophiraphidites, sp. 



(Plate I, figs. 6—9). 



Acerate spicules gradually tapering from the centre to 

 either end; sinuous and curved in a great variety of forms. 

 Some specimens have the main portion of the spicule nearly 

 straight and the extremities abruptly bent in opposite direc- 



