ADDITIONS AND CORRECTIONS. 199 



iRte rays attenuating regularly to their apices. Spicula of" 

 the crust simple, minute, and fusiform, having their surfaces 

 irregularly tuberculated, and their terminations very obtuse. 



" This sponge is found attached to the Thatcher, and other 

 rocks in the neighbourhood of Torquay about low -water-mark. 

 The parts of the cinist which are most exposed are of a dark 

 gray colour, sometimes almost approaching black, while the 

 marginal portion near the base is frequently of a light gray 

 and occasionally almost white. The crust varies from about 

 a quarter to half a line in thickness. The interior substance 

 is of a dull yellow colour, firm in texture, and very much re- 

 sembling the crumb of bread in its appearance. It is traversed 

 b^"^ numerous large excm-rent canals of about the tenth of an 

 inch in diameter, which pass in a tortuous direction from the 

 base of the sponge to the most elevated parts of its surface, 

 where they terminate in depressed areas, which are sometimes 

 surrounded by a slightly elevated marginal ring. These ori- 

 fices are frequently disposed in parallel lines, which occupy the 

 summits of the ridges that intervene between the depressed parts 

 of its surface. 



" The great variety that exists in the form of the spicula 

 of this species is very remarkable. The most common is that 

 of a simple slightly curved cylindrical spiculum, of equal di- 

 ameter throughout its whole length, with hemispherical termi- 

 nations. Occasionally, but not very frequently, there is a 

 single spiculum to be seen, in which there is a gradual attenua- 

 tion towards one end, but in all the cases that I have observed 

 of this description, it does not terminate acutely, but as in the 

 noi-mal form, hemispherically. Among the common forms there 

 are frequently to be observed large triradiate and irregularly 

 branched spicula, which have their ^;adii usually terminating 

 in a simple point; but they are sometimes bifurcated. The 

 central cavities are distinctly visible in these spicula, and in the 

 compound ones there is a free communication between all their 

 parts. In some of the spicula the centi-al cavity is much larger 

 than in others, and it may be observed with great advantage if 

 a small portion of the sponge is burned to a white ash in the 



