272 



M. K. A. Zittel on 



difference in the circumstance that in Astylospongia more 

 tlian six rays generally issue from one nodal point. A posi- 

 tive difference between Martin's description of the skeleton of 

 AstyJospongia and my own relates to the nature of the 

 " crossing- nodes," which are described by me as solid and by 

 Martin as hollow. In this ' Jahrbuch ' (1877, pp. 709, 

 710) I have explained the occasional occurrence of hollow 

 nodes as a consequence of the state of preservation, and I 

 still think I must adhere to this opinion. In another point, 

 however, Martin has completed and corrected my observa- 

 tions. The ramification of the ends of individual bars of 

 the skeleton occurring in A. piluJa I have since seen not only 

 in the preparation kindly furnished to me by Prof. Martin, 

 but also in sections of other species. This forking is really 

 not the result of later actions, as I formerly thought, but 

 evidently an original peculiarity of the skeletal elements, and, 

 indeed, the solid nodes are ])roduced entirely by the amalga- 

 mation of the forked extremities of from six to nine bars. Of 

 this the excellent figure given by Hinde [I. c. pi. xxiii. iig. 1 h) 

 leaves scarcely any doubt ; but the very accurate drawings 



Fig. 1. 



Fie 



Fig. 1.^ — Skeleton of Asfj/lospongia jn-amorsa, Goldf., from the Upper 

 Silurian of jNorth Germany. 



Fig. 2.^Skeleton of Palaomanun cratera, F. Rom., Upper Silurian, Ten- 

 nessee. 



Eularo-ed 25 diameters. 



which Mr. C. Schwager has had the kindness to prepare for 

 me show very instructively the mode of formation of the 

 " crossing nodes " in both Astylospongia (fig. 1) and Palcco- 

 manon (tig. 2). 



Ur. Hinde thinks that he can distinguish two kinds of nodes 

 in As/ylosjjongia, some produced by the amalgamation of the 

 slightly forked ends of the skeletal corpuscles, while the others 



