M. K. A. Zittel on Fossil Ilexactinellida. 501 



LXIII. — Studies on Fossil Sponges. — I. Hexactinellida. 

 Bj Karl Alfred Zittel. 



[Continued from p. 424.] 



Revision of the Genera of the Fossil 'Hexactinellida^ . 



A. DiCTYONINA, Zitt. 



Family 1. Astylospongidae. 



AsTYLOSPONGiA, Fercl. Rom. 

 Silur. Faima des westl. Tennessee, p. 8. 

 Sponge-bocly globular or thickly disciform, free, without a 

 point of attachment. Central cavity small, slightly depressed, 

 or entirely wanting. Water-circulation system composed of 

 numerous parallel canals running from the periphery towards 

 the centre, and vertical canals parallel to the periphery oi the 

 sponge-body. Skeleton consisting of coalescent sexradiates 

 with solid crossing-nodes. Latticed framework irregular, with 

 polyhedral triangular or quadrangular meshes. Usually 

 arms of several neighbouring sexradiates attach themselves to 

 one crossing-node. 



Astylospongia prmmorsa, Goldf. sp., Rom. I. c. i. 1. 

 A. castanea, Rom. Sil. Fauna von Sadewitz, iii. 3. 



Pal^omanon, F. Rom. 

 Sil. Faun, des westl. Teim. p. 12. 



Differing from the preceding genus only by the basin -like 

 shape, the wide central cavity, and larger ostia on the sides. 



Palmomanon cratera, F. Rom. I. c. i. 4. 



Protachilleum, Zitt. 



Sponge-body agariciform, stalked ; upper surface arched, 

 without a central cavity. Skeleton consisting of large coales- 

 cent sexradiates with thickened crossing-nodes. 



•\ Protachilleum Kayseri, Zitt., Kayser, Beitr. zur Geol. und 

 Pal. der Argent. Republik, ii. 1, p. 22, Taf. v. fig. 10. 



* In the case of the genera furnished with diagnoses, I have myself, 

 with few exceptions, examined the microstructure. (j-enera of which 

 uo original speciinens were accessible to me are cited without further 

 remarks, but with a reference to the original description. No synonymy 

 has been attempted ; but under each genus one or more typical species 

 are given as examples. \Mien a species was only known to me by figure 

 and description an t is appended to the name. Those species of which I 

 have been able to exanune original specimens of a previous author are 

 indicated bv an *. 



