BRITISH SPONGIADiE. 363 



membrane appears to envelop the whole of the sponge ; it 

 is thin, translucent, and abundantly coated with sarcode, 

 but rather sparingly furnished with tension spicula irre- 

 gularly disposed on its surface. Beneath the dermal mem- 

 brane the interstitial spaces are regularly furnished with 

 membranes, coated with sarcode, and sparingly furnished 

 with tension spicula, but the membranous tissues appear to 

 fail at about one sixth of the diameter of the branch within 

 the dermal membrane; below this part they only occa- 

 sionally make an appearance, and are frequently entirely 

 absent for a considerable space ; but where they do thus 

 appear in detached patches, they exhibit the usual amount 

 of sarcode and spicula, and the reticulated structures are 

 also abundantly coated with sarcode. 



This species varies considerably in its structural develop- 

 ment, in different localities. In exposed situations the fibre 

 is generally stouter, but not more abundant in spicula than 

 sponges from quiet and protected localities. In some 

 specimens from the river Orwell, about four miles below 

 Ipswich, the fibre was exceedingly delicate, or entirely 

 obsolete, so that a section might have readily been mis- 

 taken for that of an Isodictya. Dr. Johnston, in his ' His- 

 tory of British Sponges,' page 170, and Montagu, in 

 Wernerian Memoirs, vol. ii, p. 94, describes Spongia levi- 

 gata ; the latter author says : " This is the most dehcate of 

 all the soft British sponges ; when compared with either 

 Oculata or Dichotoma, their texture is extremely coarse.^' 

 He also says : " The only piece of this sponge that has 

 come under observation is tubular throughout, &c." 



The specimen in Montagu's collection, now in the pos- 

 session of Professor Grant, of University College, labelled 

 Spongia laevigata, in the same handwriting as the other 

 specimen of that collection, consists of several small 

 branches of the young of Halichondria oculata of Johnston. 

 It agrees perfectly in the form and proportions of the 

 spicula, and in the arrangement of the rest of the tissues, 

 with well known specimens of the young of that species. 

 The extreme variations that occur in Hal. oculata, both in 

 form and degree of rigidity, renders the differential cha- 



