52 Cincinnati Society of Natural History. 



Only one fragment of a specimen was used l)y Mr. Ulrich in 

 his description. 



Order Spongida. 



One of the lowest orders of animals, consisting of an aggre- 

 gation of minute beings, together forming a soft mass, with 

 spiculae of various forms, or having a silicious skeleton filled 

 witli sarcode ; this sarcode or protoplasm traversed by tubes 

 of varying size, serving to convey nourishment to the indi- 

 viduals of the mass. 



As fossils the members of this order sometimes occur as 

 amorphous and irregular masses (this is frequently the case 

 in the Cincinnati group) ; sometimes the spicules forming the 

 original skeleton are alone preserved; and sometimes the 

 external frame-work is so well preserved that the species can 

 be referred to existing orders or families. Generally it is 

 necessar}' to study the minute structure by means of micro- 

 scopic slides to determine the generic relations of the forms. 

 Occasional!}' species occur in rounded or globular masses, 

 which were evidently free growing, or attached by a single 

 point to the rocks. Some were anchored in the mud by 

 bundles of silicious spicules. 



The modern arrangement of fossil sponges is by means of 

 the spicules. In many of the genera found in the Cincinnati 

 group, spicules have not been observed, and consequently 

 any strictly scientific arrangement is not now practicable. 

 That which follows is, therefore, largely, if not wholly, arti- 

 ficial, though it has been the endeavor to group together those 

 genera of which the spicules are known, or which seem to 

 belong together. There have been included in the group two 

 anomalous genera, of uncertain position, viz : Pasccoliis and 

 Rcccpiaculitcs, while another group, which has sometimes been 

 placed with the sponges, St roniatoporoidca , is left for future 

 consideration. 



Key to Genera. 



a. Free; conical, globular or cylindrical. 



t Surface without plates. 



I. Astylospongia — Round, unattached, witli minute external 

 pores; spicula; star-shaped. 



