198 ADDITIONS AND CORRECTIONS. 



than I had previously been able to use, I found them to be 

 formed like a pin with a distinct head, and most of them per- 

 forated with a central canal. 



Halichondria sevosa, p. 147, 



The spicula are fusiform, curved, tapered to a sharp point at 



each end : they are all alike in form, and not very dispropor- 



tioned in size. 



Halichondria albescens. 



Character. Sponge Jihro-Jieshy, simple, pearshaped 

 with a subterminal osculutn ; spiculum short, slightly curved, 

 linear hut acute at both ends. 



Plate XX. Fig. 8, 8. 



Hab. Parasitical on Sertulariae in Berwick Bay. 



Sponge about half an inch in height, simple, pearshaped, fibro- 

 gelatinous, solid and almost transparent, of a watery-white colour, 

 apparently smooth, but the magnifier shows it to be subvillous 

 and minutely granulated without any perceptible pores. There 

 is usually a single osculum near the apex, circular with a plain 

 rim. The spicula are connected in a reticular manner and in- 

 terv.oven amid the organic mucus : they are neat, short, dif- 

 fering very little in length, but some are about twice as thick 

 as others. The species may be placed next to H. fucorum. 



Halichondria Johnstonia. 

 Bowierbank, MS. 

 Description. — " Massive, sessile, surface undulating, en- 

 crusted. Terminations of the excurrent canals disposed on 

 the most elevated part of the surface, depressed, sometimes 

 bounded by a slightly elevated marginal ring. IncmTent canals 

 inconspicuous. Colour of the crust slate-gray ; of the interior 

 substance dull yellow. Spicula of the skeleton mostly simple 

 and slightly curved, rarely attenuating towards their ends, but 

 usually of equal diameter throughout their whole length, having 

 hemispherical terminations : sometimes, but rarely, triradiate 

 or irregularly branched. Spicula of the flesh minute, stel- 



