SILICISPONGIAE— LITHISTIDA 



55 



Folyjerea From. ; AstroclcuUa, lliecosiphonia, Colymmatina Zitt. ; Turonia Mich. ; 

 riinthosella Zitt. (Fig. 54). Cretaceous. Discodermia Boc. ; Rhacodiscula Zitt., 

 etc. Cretaceous and Tertiary. 



Rhagadinia Zittel (Fig. 55). Auricular, plate- or bowl-shaped, short- 

 stemmed. Both surfaces traversed by irregulär branching furrows, in which 

 the canalicular Ostia are situated. Skeletal elements four-rayed, sometimes 

 uniformly or only distally covered with tuberculous knobs, and with digitate 

 extremities. Dermal spicules in the form of six-lobed disks, provided with a 

 short shaft, and minute, multifid tetraclons. Upper Cretaceous. 



Suborder2. EUTAXICLADINA Rauff. 



Skeleton composed of four-rayed spimles with three equally developed simple or 

 hifurcate rays which terminale distally in root-like fibres ; and one abbreviate, inßated 

 fourth ray (ennomoclon). Axial canals probably in all of the rays. Skeletal elements 

 invariably arranged in either parallel or alternating rows, and unifed by zygosis into 

 a network with triangulär or irregulär meshes ; spicular nodes greatly inflated. 



Nearly all the genera are Silurian ; a few (Mastosia, Lecanella) occur in the 

 Upper Jurassic. 



^yCS^^ 



Astylospongia praemorsa (Goldf.). In erratic block from Mecklenburg, a, Sponge, partially cut into, natural 

 size; b, Skeleton, 12/^ ; c, Portion of same highly magnified. 



Astylospongia Koem* (Figs. 56, b7a). Spherical, with shallow depression on 

 the summit ; base evenly rounded, unattached ; probably fastened by means 

 of anchoring fibres. Large-sized canals directed parallel to periphery in the 

 outer portion of the body, vertical in central 

 portions ; besides these there are numerous fine 

 radial canals which terminate in pores all 

 over the periphery. Skeletal elements with 

 four smooth elongated rays, one or all of 

 which brauch dichotomously just above the 

 junction with the shorter arm. Spicular 

 nodes thickened into large knots. Ordovician 

 of the Russian Baltic Sea Provinces, and 

 Silurian of Sweden and North America (not- 



ably in Tennessee), usually chalcedonised. Also in erratics in the Diluvium 

 of Northern Germany. 



Fig. 57. 

 a, Detached skeletal dement of Astylo- 

 fponriia, i'-^o/j ; b, Detached skeletal ele- 

 ment of Hindia, 80/^ (after Kauff). 



