S36 Dr Coldstream's Additions to the 



so that the outline of the whole mass is conical, and resembles 

 that of some Buccina. (Fig. 4. Plate II, is a sketch of a sec- 

 tion of the mass, shewing the position of the Turritella, and the 

 cavity in the sponge). This cavity was inhabited, in both 

 specimens found, by the common hermit-crab. Externally, in 

 one specimen, there are three fecal orifices, in the other only 

 one. The surface of the spiral cavity is smooth ; and, near the 

 shell, it is perforated by numerous small holes. The spicula 

 are slightly curved, pointed at one end, and terminated at the 

 other by a round head. (Their outline is represented in Fig. 5.) 



The history of these sponges I presume to be this. The crab 

 takes possession of the Turritella, when young ; the sponge 

 then attaches itself to the shell, and, as it grows, is forced, by 

 the motions of the crab, to assume a spiral form, with a cavity 

 enlarging towards the mouth, corresponding to the progressive 

 development of its crustaceous inhabitant. 



Montagu, who first described this species, found it generally 

 in the very same circumstances as those I have just described ; 

 but he says, that, in every specimen which he obtained, the 

 sponge had spread within the aperture of the old shell to which 

 it was attached ; and that, in some cases, it seemed to have in- 

 creased so much internally, notwithstanding the motions of the 

 crab, as to force the latter to remove to another shell (Wern. 

 Mem. ii. 102.). In my specimens, the sponge does not spread 

 within the aperture of the shell. 



Actinea maculata, (Adams, Linn. Trans, v. 8.) *. General 

 mass of the animal flattened and extended ; thickness at the oral 

 disc three-tenths of an inch, diminishing towards the circum- 

 ference of the base ; longest diameter of the base about three 

 inches ; margin minutely crenated ; colour of the body, near the 



• This has been given as a synonyme of A. sulcata^ (Flem. Brit. An. p. 498, 

 and Diet, des Sciences Nat. Ix. p. 294); but the characters of the species here 

 described do not correspond with those assigned to A. sulcata, while they agree 

 closely with the description of the maculata of Adams. In the A. sulcata, the 

 tentacula are greenish, and longer than the body ; in the A. maculata, they 

 are white, with a faint streak of brown, and shorter than the body ; the first 

 has the oral disc dentated, the latter has it plain. Lamarck (An. sans Vert, 

 iii. 69), gives the specific name of maculata to a species from the Red Sea, but 

 neither the characters assigned to it, nor the figure in the Encyclopedie, 

 (PI. 72, f. 10), correspond with those of our animal. 



