246 Cincinnati Society of Natural History. 



Order. SPONGIDA. 



One ot" tlie lowest orders of animal life, consisting of an aggre- 

 gation of animalcule; forming a soft, mass with spicuke of various 

 forms, or possessing a silicious skeleton filled with sarcode. This 

 sarcode is traversed by tubes of varying size, serving to convey 

 nourishment to the individuals. 



As fossils, they occur in amorphous masses of irregular shape 

 and variable size, showing little or no structure on the exterior 

 beyond the tube openings or oscular, internally often of layers of 

 matter separated by interlamellar spaces, the tubes jjenetrating these 

 vertically. The internal structure can only be studied by means 

 of thin sections, examined under the microscope. 



The remains of a number of genera have been found in the 

 rocks of the Cincinnati Group. The ten described genera are here 

 reduced to eight, but no account is taken ot those which have 

 been named and not described. The following keys and descrip- 

 tions are offered as a contribution to the study. The number of 

 species will no doubt be increased on a further study of more 

 material. 



SYNOPSIS OF GENERA. 



1. Free, irre(;ul.4r or spherical: extern..\i. t)PEMN(;s ro 



PORES MINUTE OR WANTING. 



a. Surface without plates. 

 Round, unattached, with minute external pores. 



I. Astylospongia. 



Irregular, generally compressed, and ha\ing the appearance 

 of a number united in a cluster. 2. Pattersonia. 



Body circular, with arms. 3. Brachiospongia. 



b Surface covered icitii plates. 



Having an apparent base : plates polygonal or hexagonal, with- 

 out special arrangement. 4. Pasceolus. 



Plates imbricated, arranged in coiu;enlric, intersecting lines. 

 5. Ischadites. 



Plates cylindrical, blunt: arranged in c(jncentric lines. 



6. Receptaculites. 



II. Incrustini; : external pores conspicuous. 



Formed of thin layers or laminre ; jjores with external open- 

 ings (osculai). 7. Stromatopora. 



Formed of thin, irregular laminae ; tubes without walls, perfo- 

 rating laminae and interspaces, but not continuously. 



8. Stromatocerium. 



