18 



^[r. W. J. Sollas on Stauronema, a neio 



the Ventriculite lantern. I notice, however, in addition to 

 the four spines just mentioned, others (fig. 5, c) which appear 

 to radiate from the centre of the spicule, one between each 

 angle of the rays ; so that altogether the structure is a very 

 puzzling one, and difficult to work out, because I find no other 

 clear example of it. 



Fig. 5. 



Pig. 5. Siliceous casts of sexradiate canals oi Stauronema : a, overlapping 

 i^ rays; b, three accessoiy spines; a fourth is concealed on the opposite 

 "^X^ side of the ray ; c, spine projecting from the centre of the cast. 



As the skeletal network is traced further inwards, the calcite 

 inside the fibre becomes replaced by silica (fig. 7), and the silica 

 which represents the original spicule by iron pyrites (fig. 7,5). 



Fig. 6. a, botiyoidal surface of fibre replaced by calcite ; b, siliceous 

 cast of spicule ; c, radiately crystalline silica of intermesh. 



The original fibre then vanishes altogether ; the botryoidal sur- 

 faces no longer define it, but, growing far away from their 

 original position and nearer to one another, diminish the inter- 

 meshes into a narrow fibre-like reticulation, and widen the 



