25G PALAEONTOLOGY OF ILLINOIS. 



The following list of characteristic Lower Trenton fossils have 

 been recognized in the sponge layer: 

 Buthotrephis succulens Hall. 

 Palaeophycus simplex Hall. 

 Monotrypa undulata Nicholson. 

 Homotrypa arbuscula Ulrich. 

 Poteriocrinus gracilis Hall. 

 Strophomena camerata Conrad. 

 Strophomena deltoidea Conrad. 

 Streptorhynchus filitextus Hall. 

 Orthis bellarugosa Count d. 

 Orthis pervetus Conrad. 



O. (Platystrophia) lynx Eichwald (small var.)- 

 Raphistoma lenticulare Emmons. 

 Pleurotomaria rotuloides Hull. 

 Pleurotomaria subconica Hall. 

 Fusispira vittata Hall. 

 Fusispira subfnsiformis? Hall. 

 Subulites elongatus Conrad. 

 Murchisonia gracilis Hall. 

 Maclurea bigsbyi Hall. 

 Ormoceras tenuifilum Hall. 

 Lituites undatus Emmons. 

 Cyrtoceras subannulatum D'Orbigny. 

 Illsenus ovatus Conrad. 



ANTHASPIDELLA nov. gen. 



Sponges compound, saucer or funnel-shaped, supported by a 

 short sub-cylindrical stem. Both surfaces of sponge wall with 

 numerous inosculating radiating channels. As growth proceeds 

 those of the upper surface are arched over by the spicular skel- 

 eton and form radial canals, which, by bending downward at 

 their outer extremities, pass through the sponge wall, and open 

 into the channels of the lower surface. These radiating canals 

 are closely arranged in vertical series, each series being sepa- 

 rated from the others by vertical sheets composed of spicular 

 structure. The canals of each series communicate with each 

 other sparingly, but more freely with those of the next series. 

 Upper surface presenting a greater or less number of oscula, 



