238 A MONOGRAPH OF THE 



in all parts alike of the dermal surface. The reticulation 

 of the skeleton contain but very few spicula, and it is very 

 difficult to distinguish its true characters in consequence of 

 the extreme abundance of the tension spicula, and it is only 

 in recently produced portions of the skeleton that its reti- 

 cular skeleton can be satisfactorily observed. These pecu- 

 liarities in its structure cause it very closely to simulate the 

 organization of a Hymeniacidon, but the short proportions 

 of the spicula, and the close texture of the internal cavities 

 of the sponge, greatly induce an observer to doubt its 

 belonging to that genus, and a more careful examination 

 wiU. rarely fail to identify portions of the reticulations of 

 the skeleton. The only species in the same division of 

 Halichondria with which this sponge is liable to be con- 

 founded is H. inconspicua, but the difference in the length 

 and proportions of their spicula will, on a comparison, 

 always distinguish them. Those of H. inconspicua is in 

 length as five to six to those of H. incerta, and at the 

 same time, although longer in the latter, they are less in 

 diameter than those of the former. 



7. Halichondria coalita, Johnston. 



Spongia coalita. Grant. 



Sponge. Sessile, irregularly latticed by rounded or com- 

 pressed inosculating branches. Surface smooth. 

 Oscula simple, dispersed, few in number. Pores 

 inconspicuous. Dermal membrane pellucid, abun- 

 dantly spiculous; spicula subfusiformi acerate, variable 

 in length and diameter. Skeleton. Interstitial spaces 

 rather uniform. Spicula same as those of the dermal 

 membrane, very variable in length and diameter. 



Colour. — Light gray. 



Habitat. — Coast of Devon, Montagu. Frith of Forth, 

 and Coast of Sheppey, Dr. Grant. 

 Examined. — In the dried state. 



