NORTH AMERICAN PORIFER^. PART II. 507 



ness the determination of the pigment particles to the opposite or cloacal pole, as described 

 by Barrois. This coloration has been seen by Barrois, however, in his Verongia rosea, 

 and the area is figured as a bare space, PL 15, fig. 41, and has been observed by Carter, 

 Barrois and myself, in several different species of the true siliceous sponges and Chalinulse, 

 as a bare projecting knob at the cloacal pole, which invariably appears to be imperforate. 



DESCRIPTIONS OF GENERA AND SPECIES. 



Spongia Auct. 

 Euspongia Bronn. Caccospongia Schmidt. 



The skeleton is composed of solid elastic fibres. The structure is irregularly radiatory. 

 The primary fibres, those having their origin in the external integument, are usually 

 though not invariably more or less radiatory, but the secondary, or connecting fibres, are 

 excessively irregular, and generally very closely intertwined. The primary fibres are 

 particularly noticeable on the inner side of the walls of the excurrent openings. A very 

 regular structure of the skeleton is found more or less in the walls of the larger cloacal 

 canals and in the young of nearly all species, and in the adults of some undoubted specimens 

 of Spongia, but, as a rule, there is no very definite arrangement, like that in Spongelia. 

 The specimens, however, in which a radiatory arrangement of the primary fibres cannot 

 be detected, are exceptional among the Florida sponges, though perhaps not so common as 

 among the Mediterranean forms. The skeleton exhibits a very rough surface. This is due 

 to the development of large projecting masses of the secondary fibres, which are separated 

 by horizontal channels of greater or less depth. The primary fibres protrude above the 

 surface of the cushions or ridges thus formed, carrying with them more or less of the 

 secondary fibres, and forming a series of sub-dermal or superficial tufts, giving the skeleton 

 a pecularly hirsute aspect. In some sponges these, like the cushions or ridges, are 

 absent, though I have failed to find any of this genus in which both have been wanting ; 

 i. e., a specimen with a perfectly smooth, even surface. 



This structure of the surface, when it is covered, as in the livino: state, bv the external 

 membrane, gives a very peculiar aspect to the subdermal region .This appears to be under- 

 mined with innumerable holes and channels, which open beloAV into the water system, and 

 externally by means of pores through the dermal membrane. These pores are very numer- 

 ous, quite permanent in their position, and though irregularly scattered over the sides 

 of the mass, often remain open even in dried specimens. The cloacal canals are few in 

 number but exceedingly large, and the interstitial canals very numerous and not compar- 

 atively very small. The large excurrent apertures are ii-regularly scattered about, but 

 almost always on the upper side of the colony. 



The dermal membrane in a living condition is of a dark brown or very dark purple or 

 black color. The external layer is usually more or less filled with whatever sediment 

 may be prevalent in the water, and, especially in the West Indies, with the siliceous spicules 

 of other sponges. A sort of selection also appears to be exercised in favor of the simplest 

 and finest forms of spiculse, which I presume are more abundant in the surrounding 

 water. These, together with minute fragments of stone, pass into the substance of the 

 primai-y fibres, which are rarely free from such impurities. The secondary fibres, owing 

 to their mode of deposition within the ectoderm are, however, always clean. 



