702 
MR, S. J. HICKSON ON THE CILIATED GROOVE 
In the Primnoacese I have shown that there is no siphonoglyphe, and the negative 
evidence of other authors affords us strong evidence for supposing that it is absent in 
the Gorgonacese. In both these families there is only a thin layer of ccenenchym 
covering the solid axis. If these two facts are mutually dependent upon one another, 
as I suppose them to be, there is sufficient reason for separating those forms which 
have only a thin ccenenchym covering the axis, and into which the polyps are never 
completely retracted, and in which there is no siphonoglyphe, into a distinct group. 
This group might retain the name of the Gorgonidse, whilst other genera which do 
not possess these characters and which were formerly included in the Gorgonidse, 
might be placed in another group of the Alcyonaria altogether. 
Provisionally, then, the Alcyonaria might be divided into the following groups :— 
1. The Pro to-Alcyonaria, containing the simple isolated genera. 
2. The Stolonifera containing those forms with stolons such as Tubipora, 
Clavularia, Sarcoclictyon, &c. 
3. The Pennatulida constituted exactly as it is at present. 
4. The Gorgonidse, containing the Primnoacese, Gorgonacese, and the other 
families which possess no siphonoglyphe. 
5. The Alcyonidse containing all the remaining Alcyonarians. 
GORGONID/^ 
PENNATULIDA 
PROTO-ALCYONARIA 
