426 Prof. W. J. Sollas on the 



XLIX. — Tlie Sponge-fauna of Norway ; a Report on the 

 Rev. A. M. Norman'' s Collection of Sponges from the Nor- 

 icegian Coast. By Prof. W. J. SoLLAS, M.A., F.R.S.E., 

 &c. 



[Plate XVII.] 

 [Coutinued from p. IGo.] 



Tetilla cranium (contiuued). 



Before proceeding to the description of the next sponge it 

 will be necessary to add, by way of appendix, a- few words on 

 the generic designation of this species. I had indeed hoped 

 that its title Tetilla was inalienably joined to it ; but unfortu- 

 nately that is not the case, since it is not the type of the genus. 

 This place is occupied by T. euplocamus^ O. S., on which, in 

 in 1868, the genus was founded. This species, indeed, en- 

 joys a name which cannot be changed, but not T. cranium • 

 let any difference of generic importance be discovered between 

 it and the type, and T. cranium must find a new generic 

 name. The existence of such a difference has already been 

 proclaimed by O. Schmidt, who regards the possession of an- 

 choring filaments by T. e^iplocamus^ jiolyura^ radiata, and 

 snbmersa as a generic character, uniting them together, to the 

 exclusion of T, cranium. As a matter of course, T. cranium 

 should receive a new generic name ; but, as a matter of fact, 

 the new name has been found for the type and its congeners, 

 while the old one is retained by the residual T. cranium. 



Whatever special advantages this plan may possess are 

 counterbalanced by its contravention of a recognized custom, 

 and its consequent tendency to throw our nomenclature, 

 which is based on recognized custom, into confusion. The 

 oftener general rules are broken the less binding do they 

 become; and the natural result is anarchy. The taunt of 

 being a "purist" in these matters is a reproach to glory 

 in ; for till we have the absolute despot, desired by a writer 

 in ' Nature,' to regulate our terminology we shall do well 

 to make the best use we can of an existing substitute; and 

 that is loyal and implicit obedience to those few simple 

 rules which have approved themselves to the general sense of 

 biologists, and of which an excellent summary is given in the 

 ' Stricklandian Code,' published under the approval of the 

 British Association. The practical application of this moral 

 excursus is obviously that Tetilla euplocamtis should retain its 

 generic name, and if a new one is necessary it should be found 

 for T. cranium. But I greatly doubt the necessity ; for the 



