AlcyOnidium. 
Z. ASCIDIOIDA. 
801 
tinolog. 525, pi. 92, fig. 1 Ulva diaphana, Eng. Bot. pi. 2G3. With, 
Bot. Arrang. iv. 121. Hull, Brit. FL ii. 312. Lam. and Decand. Flor. 
Fran^ ii. 6 Alcyonidium diaphanum, Lamour. Soland. Zooph. 71. 
Gray Brit. PI. i. 353. Hook. FI. Scot. ii. 75. Loud. Encycl. PI. 928, 
no. 15045 Al. flavescens, Loud. Encyclop. PI. 928, no. 15046 
Halodactylus diaphanus, Farre in Phil. Trans, an. 1837, 405, pi. 25 and 26. 
Hab. Deep water, attached to old shells and stones. “ Margate 
in the island of Tanet,” Johnson. “ Prope Margate in insula Tha- 
net Cantio adjacente primum observavit Johnsonus, postea D. Dale 
in insula Mersey, and D. Doody in insula Shepey,” Ray , “ Satis 
copiose reperitur posteriore insula, sed longe copiosius observatur in 
insula Thamesis ostio altius adjacente, Grain vocata,” Dillenius. 
“ In the month of August 1752, there was so great a quantity of it 
driven near Sheerness, in the Isle of Sheppey, as to clog the fisher- 
men’s nets, and interrupt their fishing,” Ellis. Isle of Anglesea and 
Walney, Hudson. Lowestoffe, Woodward. Leith shore, Jameson , 
where Dr Coldstream tells me it is sometimes very abundant. Very 
rare in Berwick Bay, G. J. Orkney islands, Dr Pat. Neill. 
The polypidom is attached by a narrow base to the substance from 
which it grows, and rises to the height of from 6 to 12 inches, “ some- 
times attaining the length of two or three feet.” It resembles a com- 
pact sponge, but is more pellucid and gelatinous ; sometimes simple 
and entire, usually branched ; the colour, as is well observed in Eng- 
lish Botany, varying from a very pale brown, almost like that of wet 
sea-sand, to a clear yellow ; in the latter case the polypidom has 
exactly the appearance of barley-sugar of the paler kind. The sur- 
face is smooth and speckled with minute dots produced by the 
dark bodies of the inhabitant polypes, which protrude their ten- 
tacula through angular apertures, and are all placed immediately un- 
derneath the skin, for the centre of the polypidom is a clear transpa- 
rent jelly traversed with corneous fibres forming a very wide and ir- 
regular net-work. The polypes are so intimately connected with 
their cells that it is almost impossible to remove them without mu- 
tilation. They have 16 filiform tentacula, disposed in a single 
circle, which are capable of being retracted within the cell. “ The ten- 
tacula are sixteen in number, (occasionally fifteen,) fully two-thirds 
the length of the body of the animal, and extremely slender and 
flexible. When expanded they are frequently seen to roll up closely 
upon themselves, even down to their base, the revolution taking 
place either inwardly or outwardly, and in one or more arms at the 
same time. Their full expansion affords a more perfect campanulate 
form than is usually met with in this class, each of the arms having 
