Oenus of Fossil HexactinelUd Sponges. 23 



cation of the Vitreoliexactinellidse according to the characters 

 of their skeletal network. 



I. Sexradiate skeleton-spicule always rectangular. Stauronemata. 



(a) Skeletal network witli simple nodes 



(1 ) one layer in thickness Farrea. 



(2) several layers thick Stauronema. 



(b) Skeletal network having the nodes complicated by the presence of 

 an octahedral lantern about each one VentricuUtidce, 



including Myliusia Grayi. 



II. Sexradiate skeleton-spicule with rays making any angle with each 



other. APHROCALLISTIDiE. 



Aphrocallistes, Dactylocalyx*^ Iphiteon*, Stromatopora {Callodictyon, 

 SoUas, n. g.) concentrica. 



III. Skeleton-spicules cemented into ladder-like fibre. Euplectellidje. 

 JEuplectellu, Sympagella, 



Vitreoliexactinellidse. 



Genus Staueonema (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, quincunciallj 

 arranged, patent where the oscular plate is free, concealed 

 beneath a superficial 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 sexradiate, 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. This species I dedicate with great pleasure to my 

 friend and instructor Mr. H. 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 J but the character of the network agrees with that of Aphro- 

 callistes. 



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

 which evidently belongs to this genus j but it is not well enough preserved 

 for specific determination. 



