VESICULARINA : VESICULARIADJ5. 367 



it requires a practised eye to distinguish them. I have been induced 

 to consider this species as distinct from the genus Alcyonidium, to 

 which it bears a near relation, for the following reasons: — 1st. The 

 number of the tentacula, a character which I have found to be con- 

 stant, it being twenty in this and but sixteen in Alcyonidium; 

 2nd. This species never rises from the surface of attachment in the 

 form of an independent polypidom — it is invariably encrusting, 

 whereas all the species of the genus Alcyonidium do form elevated 

 polypidoms ; and 3rd. There is a difference in the form of the body 

 or organ to which I have referred in the description of the genus 

 Cycloum, it being circular in this, while it is oblong in the genus 

 Alcyonidium. 



" T have frequently noticed a species of zoophyte lining the inte- 

 rior of old shells of Buccinum undatum, and covering the under sur- 

 face of stones, which I consider to be identical with this. If a por- 

 tion of the polypidom of this species, in a living condition, be sud- 

 denly plunged into spirits, an instantaneous protrusion of the polypi 

 takes place, having their feelers arranged, as in life, in the form of a 

 graceful bell. In this state they may be kept, for a time, for the 

 purposes of future examination. The cause of this protrusion is rea- 

 dily explained. The polypes being already contracted within their 

 cells, on the application of the irritating spirit are compelled to 

 start outwards, — the only motion of which they are capable when 

 folded up within these cells." A . U. Hasscdl. 



IV. VESICULARINA. 



PoLYZOA CORNEA, J. E. Gray in Syn. Brit. Mus. 135. 



FAMILY— VESICULARIAD^. 



Since we profess to be guided, in the classification of zoophytes, 

 by similarity in the structure of the polypes considered independ- 

 ently of their polypidoms, the Vesiculariadse, notwithstanding their 

 apparent dissimilarity, must be associated in the same order with 

 Alcyonidium and Flustra. They have been hitherto united with 

 the Sertulariadas ; and, previous to our knowledge of their polypes, 

 this seemed a very natural union, for the polypidoms of both are 

 slender and plant-like, horny, fistular, and flexible, and furnished 

 with somewhat similar culls on their branches. Cut the differences 

 between them even in outward aspect are not inconsiderable ; and, 

 although it may be difficult to point out these by any description, 



