Oenus of Fossil llexactinellid Sponges. 23 



cation of tlic VitrcolicxactiuclliiU\j according to the cliaractcrs 

 of their skelctiil network. 



I. Soxradiate skeluton-spicule always rectangular. Stauhonemata. 



(«) Skeletal network witli simple nodes 



( 1 ) one liiyer in thicliness Fmrca. 



(2) sevoial Inyrrs tliiek 8tunruiieina. 



(b) Skeletal network liuviiiL' the nodes complicated by the presence of 



an octahedrul luutcrn iiuout each one '. Ventricu/itidfe, 



including Mi/litma (Jruyi. 



II. Sexi-adiate skeleton-spicule with rays making any angle with each 



other. Ai'nnuc.u.LiSTiD.i!;. 



AphroialliifteK, Dactylucaly.i-*, Iphiteon*, Stromaiopora {Callodictyon, 

 Sollas, u. g.) vuncciitriva. 



III. Skeletoii-spicules cemented into ladder-like fibre. EUPLECTELLID.*:. 

 Huplcdelia, ISyinpaycUa. 



Vitr eohexactinellidae . 

 Genus Stauronema (mihi). 



Form half-conical or half-cup-like, fan-shaped, vertical, 

 sessile, attached. 



Structure a thin oscular plate, overgrown at its base by a 

 thick posterior mass. Oscules oval or round, quincuncially 

 arranged, patent where the oscular plate is free, concealed 

 beneatii a supcrticial reticulation where attached. Excurrent 

 canals cylindrical where they perforate the oscular plate. 



Skeleton : spicule triaxial, axes at right angles to each other j 

 fibre robust, nodes scxradiate, meshes quadrilateral. 



Formation. Gault and Upper Greensandf. 



Locality. Folkestone and the Isle of Wight. 



Species: — 



1. Stauronema Carteri (mihi), type. 



Form. Posterior mass more or less rugose horizontally, ex- 

 tending as far as the lateral edges of the plate to which it is 

 attached (see p. 6). 



Remark. Tiiis species I dedicate with great pleasure to my 

 friend and instructor Mr. 11. J. Carter, who was the first to 

 explain aright the structure of the vitreohexactinellid skeleton. 



• The imbedded spicules of these two genera have not yet been ob- 

 served ; but the character of the network agrees with that of Aphro- 

 ca/tistfs. 



+ I possess a specimen from the Upper Greensand of the Isle of Wight, 

 wliich evidently belongs to this genus j but it is not well enough preaervca 

 fur specific determination. 



