370 Mr. A. H. Hassall's Catalogue of Irish Zoophytes. 



found tne number of tentacula in each polype to be the same, viz. 

 30. 



Dublin Bay : abundant on Fucus siliquosus. 



F, Hibernica. I have now ascertained that this species, which I 

 described in my Catalogue of Irish Zoophytes published in the 

 ' Annals ' for November 1840, is not a Flustra but aLepralia, which 

 I have again figured and described in this paper under the head of 

 L. pedilostoma. The figure given with the Catalogue represents a 

 posterior view of the cells, the wall of each cell posteriorly being 

 absent. The error of figuring the cells posteriorly instead of ante- 

 riorly, and the absence of the posterior wall, are thus accounted 

 for. The specimen from which the figure was taken adhered to an 

 Ascidia ; this Ascidia grew on the under surface of a rock, in re- 

 moving which, the Lepralia, which covered the rock before the As- 

 cidia, also came away, — the mouths of the cells adhering to it, and 

 the wall still remaining attached to the rock. The detection of an 

 error of this nature is almost as pleasing as the discovery of a new 

 species. 



Cellularia avicularia. This species 1 now find to be abundant in 

 the Bay of Dublin and about the neighbouring coast. 



Alcyonidimn gelatinosum. Occurs in long rope-like masses, and is 

 rarely obtained except by trawling. Rare, off Howth and Lambay. 



A. hirsutum. The polypidom of this species in its young state is 

 clavate, and not branched. As in this condition it might, possibly, 

 be mistaken for a distinct species, I have given two figures of it, one 

 representing it of its natural size ; the other is a magnified view of 

 it, wdth many of the polypi protruded. When under the microscope 

 it presented a very beautiful appearance, some faint idea of which 

 the drawing, Plate X. fig. 3, 4., is intended to convey. 



A. parasiticum. Polypidom encrusting, spongy ; cells polygonal, 

 but irregular in size and arrangement. Polypes with sixteen ten- 

 tacula. 



The nature of this production, which has long been involved in 

 obscurity, I have at last succeeded in determining. By very many 

 it was not considered to be a zoophyte at all ; I have, however, as- 

 certained, beyond all doubt, that it is a true polypiferous production 

 of the genus Alcyonidium. Dr. Johnston describes the polypidom 

 as " entirely composed of particles of sand cemented together with 

 mud or clay." Were this really its character, this fact alone would 

 be sufficient to decide that it could not be a zoophyte ; for the po- 

 lypidoms of all true zoophytes are growths, and not artificial for- 

 mations. Numerous sandy particles are certainly found in con- 

 nexion with it, but not, in my opinion, incorporated with it ; their 

 presence, I believe, being confined to cells vacant by the death of 

 the polypi. If previously dried, and then dropped into water, it im- 

 mediately sinks to the bottom, and does not remain there wholly 

 unaltered, but slowly absorbs a portion of the fluid until it has at- 

 tained its original dimensions. I also believe that I have detected 

 a few siliceous spiculee, and certainly numerous siliceous granules. 



