Form. 



83 



complex. To serve the purposes of this work we have "brouglit together in 

 figure 8 a group of the more characteristic derivative forms of the hexactin 

 spicule, which has been compiled from the illustrations given by Schulze 

 {Report Cltalletujer Expedition) and Eauff {Pala<iO>^(rmjiolo<jie). These will 

 aid in elucidating the spicular forms occurring in the Dictyspongid^ 



FiocRE 7. Spicule! of Dictyospongidae. 



The upper figure is a group of stout bean-shaped diactins from an undetermined 

 fragment at Crawfordsville, Indiana. The two lower spicules are from Griphodictya 

 epi'phanes; that at the left is an hexactin much branched at the eztremityof the rays ; 

 that at the right an umbel with deeply cleft top. All x 400. 



Vakiations and Genetic Relations of Form. 



A glance through the plates of this volume will convey an idea of the 

 multiplicity of forms under which the Dictyosponges manifested themselves. 

 Among these smooth, nodose, prismatic and annulated cups and ^•ases, the 

 smooth slender obcone as expressed in the typical genus Dicitospongia, is 

 doubtless to be regarded as the fundamental form. The primary relation 

 of this form to all the abundant expressions occurring in the Devonian 

 faunas is evident from an inspection of any well-preserved example of a 

 nodose, prismatic, annulated or other form, in all of which the early stages are 



