246 THE AMERICAN MUSEUM JOURNAL 



from a common base, and connected with each other by root-like 

 stolons, which form the attachments to the rocks on which they 

 grow. The texture of the skeleton is very fine and smooth. 



Tuba. — ^The genus Tuba is represented by two species T. 

 bullata and T. plicifera. These are more or less trumpet-shaped 

 as the name implies. The specimen illustrated on page 245 is 

 especially fine. 



The Homy Sponges (order Monoceratida) includes the sponges 

 whose skeletons are entirely made of the spongin substance. 

 The most typical and most important of these are the commercial 



FIG. 26. — THE ZIMOCCA SPONGE {Euspongia zimocca Schulze) 



Sponges. They are divided into the genera Euspongia and 

 Hippospongia. In addition to these the fine finger-like sponges 

 of the genus Chalinopsilla, the black branching skeleton of 

 Hircinia atra Whitfield (type) and the graceful cup-like specimens 

 of Stelospongia (see illustration on page 227) are worthy of note, 

 although they possess no commercial value. 



THE COMMERCIAL SPONGES^ 



The sponge of commerce is the elastic homy skeleton of 

 spongin from which all the living tissues of the animal have been 

 removed. The principal sources of supply are: 



