52 DiCTYOSPONGID.E. 



CLASSIFICATION OF THE DICTYOSPONGID^. 



The manifold vuiiations in form expressed by these sponges are accom- 

 panied by certain structural diversities ^vhich, however, do not lead far a-field 

 from the comprehensive definition elsewhere given of the indicial characters 

 of the Family. It has been, in our judgment, wise not to endow any of these 

 structural characters Avith so high value as to necessitate the erection of 

 additional Family terms, and experience indicates that few thin-walled siliceous 

 sponges of the Devonian and Carboniferous faunas will fail to find a place 

 within the limits of this Family, Dictyospongid^. The structural variations of 

 chief importance are herewith summarized and utilized as the basis of a 

 subordinate classification. 



Subfamily I. 



DlCTYOSPONGIIN^. 



Simple, vase-shaped or elongate, smooth, prismatic, nodose or annulated 

 forms with obcouical base ; with basal prostalia ; Avith or without marginalia ; 

 no basal disk ; primitive form a regulai' obcone. 



Dictyospongia, Helicodictya, 



(?) Lysactinella, lihabdosispongia, 



Hydriodictya, Ceratodictya, 



Prismodictya, Clathrospongia, 



Gongylospongia, Lebedictya, 



Hydnoceras, Lyrodictya, 



(?) Tylodictya, (?) Mastodictya. 



BoTBYODicTYA, Avliich appertains to this group in its principal characters, 

 is aberrant in the possession of a more or less complete diaphragm, not at the 

 base but near the middle of the sponge, just Ijelow the nodlferous body. 



Subfamily II. 



Thysanodictyin^. 



Cylindrical or expanding cups, with basal disk and periloph. 

 Thysanodictya, Phragmodictya, 



Arystidictya, (?) Griphodictya. 



