82 THE OCEAN WORLD. 



Many species of Spongia are described as inhabiting British seas, 

 but none of any commercial value. Kegarding them as apolypiferous 

 zoophytes, Dr. Grant has pointed out certain principles of analysis 

 on which they may be grouped, according to the arrangement of the 

 horny fibres, the calcareous and siliceous spiculse, and the distribution 

 and formation of their pores and orifices. 



I. GEOUPS OF WHICH THE CONSTITUENT STRUCTURE IS KNOWN. 



Spongia. Mass soft, elastic, more or less irregular in shape, very 

 porous, traversed by many tortuous canals, which terminate at the 

 surface in distinct orifices. Substance of the skeleton cartilaginous, 

 fibres anastomosed in all directions, without any earthy spicula. 

 Example, 8. communis (Fig. 11 [2]). 



Caloispongia (Blainville). Mass rigid or slightly elastic, of irregular 

 form, porous, traversed by irregular canals, which terminate on the sur- 

 face in distinct orifices; skeleton cartilaginous, fibres strengthened 

 by calcareous spicula, often tri-radiate. Example, 8. compressa 

 (Fig. 11 [6]). 



Halispongia (Blainville). Mass more or less rigid or friable, irre- 

 gular, porous, traversed by tortuous irregular canals, which terminate 

 at the surface in distinct orifices; substance cartilaginous, fibres 

 strengthened by siliceous spicula, generally fusiform or cylindrical. 

 Example, S. papillaris (Grant) (Fig. 11 [3]). 



Spongilla (Lamarck). Mass more or less rigid or friable, irregular? 

 porous, but not furnished with regular orifices or internal canals. 

 Example, S. fluviatalis (Linn.). 



II. GROUPS DEPENDING ON CHARACTERS OF SURFACE OR 



GENERAL FIGURE. 



Geodia (Lamarck). Fleshy mass, tuberous, irregular, hollow 

 within, externally incrusted by a porous envelope, which bears a 

 series of orifices in a small tubercular space. Example, G. gibberosa 

 (Schmeiger). 



Coeloptychium (Goldfuss). Mass fixed, pedicled, the upper part 

 expanded, agariciform, concave, and radiato-porose above, flat and 

 radiato-sulcate below; substance fibrous. Example, C. agarisidioi- 

 deum (Goldfuss). Fossils from the chalk of Westphalia. 



