SPONGIDA. 



135 



in past time. Of the fossil forms, indeed, hardly any can 

 be said to be true Calcispongice, if we restrict this name to 

 Sponges with a skeleton composed of free calcareous spicula ; 

 and some doubt attaches to even the very few forms which 

 one might be disposed to place here. Two ancient genera 

 viz., Astrceospongia and Amphispongia may, however, be more 

 specially mentioned, as being, perhaps, ancestral types of the 

 modern Calcispongice. In Astrceospongia (fig. 33, a), we have 



Fig. 33. a, Side-view of a specimen of Astrceospongia meniscus, of the natural size, Upper 

 Silurian ; ft, Spicules of the same, enlarged (after Roemer) ; c, A split specimen of Amphi- 

 spongia oblonga, of the natural size, Upper Silurian ; d, Part of the upper portion of the 

 same, enlarged. (Original.) 



a cup-shaped or discoid sponge, found in the Upper Silurian 

 and Devonian, and composed of irregularly disposed, free, six- 

 rayed, calcareous spicula, without any definite canal-system. 

 The rays of the spicules are all in one plane, and their size 

 is much greater than that of the spicules of any living 

 member of the Calcispongice, but there is no sufficient reason 

 for regarding them as having been anything but calcareous 

 to begin with, since they occur in beds in which the other 

 fossils have undergone no change. 



The genus Amphispongia (fig. 33, c) is another curious 

 type, which approximates to the living Calcispongice more 

 closely than the preceding. It is only known from certain 

 soft sandstones, of Upper Silurian age, in the Pentland Hills, 

 near Edinburgh ; and, like almost all the other fossils in the 

 same beds, its original calcareous skeleton has been dissolved 

 away, but we are not thereby justified in concluding that its 

 hard parts were primitively composed of anything but lime. 

 The general form of this sponge is that of a somewhat clavate 

 mass, between one and two inches long, and, owing to its 



