16 BRA^X'H PORIFERA 



no commercial value. Example, Grantia. (2) The silicious 

 sponges, in which the skeleton is largely silica. Example, 

 Ewpledel'la. (3) The horny sponges of commerce. Euspongia 

 group. To this group belong the half-dozen species of Florida 

 and the Mediterranean and the Red Seas. Our American sup- 

 ply comes principally from Florida and the Mediterranean Sea 



Fig. 9.— A sponge auction at Anclote. (Report U. S. F. C, 1902). 



from water not exceeding 30 fathoms deep. Examples of this 

 group are Spongia, and the fresh-water forms of the genus 

 Syongilla. 



Most zoologists make but one class of porifera; others, two 

 classes : 



I. Calca'rea. 



II. Non-calca'rea. 



