\l IK\ TRUNCATA. 9 



HABITAT. Ou Algae and shells, between tide-marks and 

 in moderate depths. 



LOCALITIES. Lamlash Bay, Arran, on Laminaria saccha- 

 rina (Landsb.) : Isle of Man, on oyster-shells, common ; 

 Ilfracombe, on weed between tide-marks ; Swanage ; South 

 Devon, not very common (T. H.) : Guernsey (Miss Re- 

 nouf), &c. 



GEOGRAPHICAL DISTRIBUTION. Bahusia; Southern Nor- 

 way (Smitt) : Madeira (J. Y. J.). 



Aetea truncata presents very different appearances in 

 different states or stages of growth. In its simplest 

 condition, the zoarium consists of lines of sessile cells, 

 distributed at intervals along a delicate thread-like 

 fibre, as in the other species of this genus. It ex- 

 hibits indeed one peculiarity : a large proportion of 

 the cells are often furnished with a tubular tail-like ap- 

 pendage, given off from the back and usually directed 

 upwards ; it varies in length, and originates about half- 

 way down the cell. And in some cases this dorsal tube 

 becomes much elongated, and supports a second cell. 

 From this second cell a slender stem or pedicle is given off, 

 which terminates in a third cell, and so on. The species 

 has taken on the habit of Eucratea (Plate II. fig. 3) . 



This erect and composite form, however, seems to be 

 comparatively rare ; more commonly, so far as I have 

 seen, the simple habit prevails. The cells are usually 

 sessile, but occasionally are borne on a short tubular pro- 

 cess given off from the creeping stem. They are of a 

 pure white colour, and very bright and glossy. The fibre 

 is of extreme delicacy, and is very minutely but very beau- 

 tifully dotted over ; the enlargements from which the cells 

 rise are slender and comparatively inconspicuous. From 

 each side of them branches are given off' nearly at right 



