Alcyonidium. Z. ASCIDIOIDA. ;3Ul 



tinolog. 525, pi. 92, fig. 1 Ulva diaphana, Eng. Bot. pi. 2G3. Wifh. 



Bot. Arrang. iv. 121. Hull, Brit. Fl. ii. 312. Lam. and Decand. Flor. 



Fran9. ii. 6. Alcyonidium diaphanum, Lamour. Soland. Zooph. 71. 



Gray Brit. PL i. 353. Hook. Fl. Scot. ii. 75. Loud. Encycl. PI. 928, 



no. 15045 Al. flavescens, Lout/. Encyclop. PI. 928, no- 15046 



Halodactylus diaphanus, Farre in Phil. Trans, an. 1 837, 405, pi. 25 and 26- 



Hab. Deep water, attached to old shells and stones. " Margate 

 in the island of Tanet," Johnson. " Prope INIargate 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 long-e 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 I2 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 olour, 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, aud are all placed immediately un- 

 derneath the skin, for the centre of the polypidom is a clear transpa- 

 rent jelly traversed with corneous fibi'es 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 



