SPONGID.E. 43 



possesses the remarkable power of excavating bur- 

 rows for itself in shells and other calcareous 

 bodies, is found in most of the secondary and 

 tertiary formations, and is sufficiently abundant 

 along the shores of the existing ocean. Since, 

 however, we are still by no means certain as to 

 what constitutes a genus among recent Sponges, it 

 is evident that even greater difficulties must at- 

 tend our investigations among extinct forms, and 

 hence, any tabular arrangement showing the 

 successive appearance and relative distribution of 

 these *^ genera '' seems to us, at present, premature. 



II. AflSaaity to Foraisiiaiifera The nature 



of the relationship between the Sponges and 

 amoebiform Ehizopods has been already alluded 

 to. Eecently, Dr. J. E. Gray has described, under 

 the names of Carpenteria and Dujardinia, two 

 remarkable attached forms of Protozoa, present- 

 ing characters intermediate between those of the 

 Spongidce and Foramninifera. Both of these are 

 furnished with conical calcareous shells, composed 

 of an aggregation of elongated chambers disposed 

 in a spiral, the orifice of the last-formed chamber 

 being placed at the apex of the entire shell. In 

 Carpenteria, the interior of the chambers " is 

 filled with a fleshy sponge-like body, strengthened 

 by numerous minute, simple, pin-shaped and 

 fusiform smooth spicula placed in bundles." In 

 both of these organisms the entire shell is pierced 

 with very many, minute, circular perforations. 



