ORDER IV SILICISPONGIAE— HEXACTINELLIDA 61 



Subfamily 2. Thtsanodictyinae Hall and Clarke. 



Thysanodidya Hall and Clarke. Subcylindrical or tapering Dictyosponges 

 with prominent projecting, rectangularly reticulating spicular bands or lamellae 

 forming series of fenestrated quadrules upon the surface. Base with basal 

 disk or broad obcone. Devonian. 



Phragmodidya Hall ; Arystidida, Adoeodidya, Griphodidya Hall and Clarke. 

 Upper Devonian and Lower Carboniferous. 



Subfamily 3. Calathospongiinae Hall and Clarke. 



Calathospongia Hall and Clarke. Stout subcylindrical cups with truncated 

 bases, probably attached by the basal margins ; contracted mesially and more 

 or less expanded at the aperture. Surface without 

 nodes. Carboniferous. 



Clepsydrospongia Hall and Clarke. Thamnodidya, 

 Cleodidya Hall. 



Subfamily 4. Physospongiinae Hall and Clarke. 



Physospongia Hall.' Keokuk group. Roemeri- 

 spongia Hall and Clarke. Eifel Devonian. (' ,,'- 



Subfamily 5. Hyphantaeniinae Hall and Clarke. 



Hyphantaenia (Uphantaenia) Vanuxem. Large, 

 circular and shallow saucer-shaped cups, composed 

 of two series of intersecting spicular straps, one 

 radiating, the other concentric. Chemung Group ; 

 New York. 



Fio. 04. 



Subfamily 6. HalLODICTYINAE Hall and Clarke. Hydiwceras hathensis Hail and 



•' ClarkR. Cliemung Group' ; Bath, 



Hallodidya Hall and Clarke. Adinodidya, Crypto- of .stronj;- iwdes and iHieiy reticu- 

 didya Hall. Chemung Group ; New York. ciadcer"''"'' ''' ^"''"' """^ ""^ 



Subfamily 7. Aglithodictyinae Hall and Clarke. 

 Aglithodidya Hall and Clarke. Chemung Group ; New York. 



Family 3. Plectospongidae Eauff. 



Thin-ioalled tubes with skeleton composed of a regular framework made up of an 

 ascending and approximately ring-like series of spicules ; the latter form rectangular 

 to quadrate, hut not very symmetrical meshes. Spicular rays^ fasciculate. Ordovician 

 and Silurian. 



Cyathophycus Walcott ; PalaeosaccMS, Acanthodidya Hinde. Ordovician. 

 Pledoderma Hinde. Silurian. 



