50 



COELEXTERATA SPONGIAE 



CLASS I 



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. 



Sub-Order B. EUTAXICLADINA. Rauff. 



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

 bifurcate rays which terminate distally in root -like fibres; and one foreshortened, 

 inflated fourth ray (ennomolcon). Axial canals probably in all of the rays. Skeletal 



FIG. 61. 



Astylospongia praemorsa, Goldf. sp. In erratic from Mecklenburg, a, Sponge, partially cut into, natural size ; 

 5, Skeleton, 12/j ; c, Portion of same highly magnified. 



elements invariably arranged in either parallel or alternating rows, and united by 

 zygosis into a network with triangular or irregular meshes ; spicular nodes greatly 

 inflated. 



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

 Upper Jurassic. 



Astylospongia, Roem. (Figs. 61, 62). 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 

 are numerous fine radial canals which termin- 

 ate in pores all over the periphery. Skeletal 

 elements with four smooth elongated rays, one 

 or all of which branch dichotomously just 

 above the junction with the shorter arm. 

 Spicular nodes thickened into large knots. 

 Ordovician of the Russian Baltic Sea Pro- 

 vinces, and Silurian of Sweden and North America (notably in Tennessee), 

 usually chalcedonised. Also in erratics in the Diluvium of Northern Germany. 

 Caryospongia, Carpospongia,, Rauft'. Ordovician and Silurian ; Europe. 

 Palaeomanon, Roem. (Astylomanon, Rauff). Like Astylospongia, but bowl- 

 shaped, with shallower and wider cloacal depression. Entire surface covered 

 with pores. Silurian ; North America. P. cratera, Roem. 



Caryomanon, Carpomanon, Rauff. Silurian ; North America. 



PIG. 62. 



a, Detached skeletal element of A stylo 

 xpmiifirt,, 120 /i ; b, Detached skeletal 

 of Hindia, 80/1 (after Hauft'). 



element 



