84 Mr. G. Busk on three new species of Polyzoa. 



venient usually to refer to the back view of them, as I have done 

 in this case. 



In habit this species bears so close a resemblance to Scrupocel- 

 laria scruposa, that to the naked eye there is veiy little difference 

 between them . The branches are a little broader, and perhaps more 

 regularly and more closely disposed. The cells are wider in pro- 

 portion to their length than in that species, and their sides, 

 especially the upper one, more square and straight. The prin- 

 cipal difference in the form of the cell consists in the existence 

 in S. scrupea of a rather deep depression or sinus on the back 

 of the cell and towards the outer margin, in which sinus is lodged 

 the vibraculum*. This organ is placed considerably more behind 

 the cell than it is in /S. scruposa, and differs somewhat in shape 

 from the same organ in that species. It is wider, flatter, and as 

 it were, more of a spatulate form. The avicularium occupies the 

 same position or neai'ly so as in that species, or perhaps is also 

 placed a little more posteriorly. An important difference how- 

 ever between these very similar species consists in the reniform 

 pedunculate operculum, which projects in front of the mouth of 

 the cell. Although this organ exists in a great variety of forms 

 in many species of Cellulariadae, and is particidarly well developed 

 in the common Scnipocellaria reptans, I am not aware that it has 

 hitherto received the attention it would seem to deserve in the 

 distinction of species : that its presence or absence could scarcely 

 be regarded with safety as a generic character, the present in- 

 stance might perhaps suffice to show, as it does not exist in S. 

 scruposa ; but of its specific importance I am convinced, from the 

 examination of many foreign species. Several species furnished 

 with this appendage and in various forms are figured by Savigny 

 in the great work on Egypt, but no allusion is made to it by 

 Audouin in the meagre text relating to those figures. 



This process does not arise from the edge of the cell (at least 

 not generally), but from the wall of the cell a little beyond the 

 margin, and it usually appears to be tubular at its origin. It 

 assumes various forms, some very fantastic, and increases in size 

 as the cell becomes older, so that in the older cells at the bottom 

 of the branches it almost entirely covers the mouth. 



In the case oiSa'upocellaria scruposa,th.e want of this operculum 

 appears to be compensated for by the greater thickness of the 

 velum, and which in that species, in the older cells, becomes the 

 seat of an increased deposition of calcareous matter. When in 

 this state, the cells anteriorly very much i-esemble those of certain 

 species of Catenicella. 



I have subjoined a figm*e of this operculum as it occurs in 



* I employ this term to signify the organs furnished with a moveable or 

 vibratile seta, as distinguished from the prehensile avicularia. 



A 



