304 Z. ASCIDIOIDA. Alcyonidium. 



from its place, and swim about hither and thither as it were endow- 

 ed with volition, turning on its axis frequently, moving- sometimes 

 on one side, sometimes on its edge, when the cilia become invisible. 

 I have seen the cilia, when the ovum was at rest, suddenly disappear, 

 withdrawn as it seemed within themselves, or under the opaque mar- 

 gin, and again be quickly protruded. By their motion they drive a 

 current of water over the surface, but this current has certainly not 

 an uninterrupted circular motion — it is rather a flowing to the sur- 

 face, and a cm'rent from it, or as Raspail would express it, an inspi- 

 ration and expiration of water. — When lying still, I have seen the eggs 

 exhibit the most unequivocal signs of irritability, contracting and di- 

 lating themselves. The ovum appears to be formed of a firm elastic 

 coat or shell filled with agranular matter ; it is opaque, excepting on 

 ■ the margin, under which the cilia appear to originate. 



3. A. ECHiNATUM, polypidom incrusting dead univalve shells, 

 the surface muricated with rough prominerit papillce or cells. Mr 

 Montagu. 



Plate xlii. Fig. 3, 4. 

 Alcyonium echinatum, Flem. Brit. Anim. 517. Johnston \n Trans. Newc 



Soc. ii. 251, pi 9, fig:. 2 L'A. herisse, Blainv. Actinolog. 525. 



Hub. Parasitical on Buccinum undatum and similar univalve 

 shells ; not uncommon. Stevenston, Ayrshire, Rev. D. Landsbo- 

 rough. Berwick Bay. 



" This species incrusts dead univalve shells exclusively ; and is 

 about the one-twentieth of an inch in thickness. When first taken 

 out of the water, it is soft and spongy, but becomes rigid on drying." 

 The surface in this state is muricated with spinous papillce, somewhat 

 less than a line in height aud rough with minute prickles pointing 

 upwards and arranged in rows. The polypes appear to have only 12 

 tentacnla. 



4. A.? PARASiTicuM, inc7'usting corallines, earthy, the sur- 

 face even and porous. Rev. Dr Fleming. 



Plate xli. Fig. 4, 5. 



Alcyonium parasiticum, Flem. Brit.' Anim. 518 L'A. parasite, Bhiinv- 



Actinol. 525. 

 Hab. Parasitical on Sertulariadse and old shells. Hartlepool, ,/. 

 Hogg. On the valve of an old Venus islandica dredged from deep 

 water at Scarborough, 3Ir Bean. Berwick Bay, rare. 



This production spreads up the stem and branches of various flexi- 

 ble corallines coating them with an incrustation of an earthy appear- 

 ance, from a line to the eighth of an inch in thickness. The sur- 



