SPONGES. 225 



Fig. 7. Spicule of Aulocopium sp.. x55. Silurian of Gotland. 



Fig. 8. Spicule of Bhizomorine sponge (Seliscothon mantelli Goldf.. Cretaceous of Ger- 

 many), showing axial canal and its division at each end ; x 55. Introduced for 

 comparison with the Anthaspidellidae. 



Fig. 9. Small portion of surface of Hindia sphceroidalis Duncan, x 55, showing mouth 

 of one of the radiating canals and three spicules. Niagara group, Spring 

 Valley, Minn. 



Fig. 10. Portion of a gutta-percha cast taken from a vertically fractured example of 

 the same ; x 55. 



So far as known, Aulocopium agrees in one character more 

 nearly with the Tetracladine and Rhizomorine sponges than do 

 the other genera here referred to the new family, the ends of its 

 spicule rays, namely, being branched. In that respect, as well 

 as in being considerably smaller, the spicules of Aulocopium 

 differ from those of Climacospongia, the rays in the latter being, 

 apparently always, simple and smooth. In none of the Trenton 

 genera could the construction of the columns be determined, all 

 the finer details having been destroyed during the process of 

 calcification. 



As regards the systematic position of the proposed family 

 every character strongly favors a reference to the Lithistida?. 

 But when it comes to saying to which of the four already 

 established families of the order the new division is the near- 

 est related, we cannot speak with the same confidence. In 

 the first place the comparatively regular form and grouping 

 of the spicules suggests the Tetracladina, but the fact that 

 these bodies are built upon a totally different plan, at once 

 negatives the idea that any very intimate relationship exists 

 here. In the Tetracladina the four arms of the spicules diverge 

 from a center at angles of 120. In the Anthaspidellidae, on 

 the other hand, the four rays are thrown off in pairs from the 

 ends of what might be called a profoundly elongated node 

 (the horizontal central bar). 



The swollen central node and the general irregularity of the 

 skeleton elements distinguish the Anomocladina. 



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