POEIFERA (sponges). 



37 



Eutaxicladina (Silurian to Jurassic) : desma with a G-allery 

 thickened central node from which proceed three or more 

 rays, expanded at the ends so as to join others (Fig. 12 A) ; 

 chief genus, Astylospongia. Anomocladina (Jurassic to 

 Eecent) : desma a rod with swollen ends from which proceed 

 three or more simple or branched rays, uniting as in Eutaxi- 



FiG. 12. — Fossil sponge spicules : Silicispongiae, Tetractinellida. Skeletal 

 spicules of Lithistida. Rhizomorina : a, b, Seliscothon ; c, Cnemidia- 

 strum. Tetracladina : d, Aulocopiimi megamorma ; e, /, Doryderma ; 

 g, Carterella. Eutaxicladina : h, Astylospongia. a, b, c, d, h, enlarged 

 40 diam. ; e, 26 diam. ; /, g, 20 diam, (After Hinde.) 



Fig. 13. — Fossil sponge spicules : Silicispongiae, Tetractinellida. Skeletal 

 ((X-e) and dermal (f-i) spicules of Lithistida. Eutaxicladina : a, 

 Mastosia. Anomocladina : b, Cylindj'ophyma. Tetracladina : c, d, 

 Callopegma ; e, Plinthosella. e, enlarged 26 diam. ; the rest 40 diam. 

 (After Hinde.) 



cladina (Fig, 13 &) ; Cylindrophyma is common in Upper 

 Jurassic rocks. Megamorina (Silurian to Eecent) : desmas 

 relatively large, curved, branching rods, either intertwining 

 or joined as in Eutaxicladina (Fig. 12 e, f, g)\ Doryderma 

 (Fig. 16 &) is abundant in the Upper Chalk. Rhizomorina 

 (Cambrian to Eecent) : desma small, usually elongate, curved, 

 with irregular branches ; these end in minute facets, which 



