sponge-fauna of Norway. 429 



siderable ; and it would be a nice point to determine how far, 

 after his published figures and description, it could be re- 

 garded as a merely MS. name ; into that question I have 

 fortunately no need to enter. That T. muricata differs in a 

 marked manner from other described species of Tethya is, 

 however, already quite clear; and Gray (iii.), who had a real 

 knowledge of the sponge, so cleai'ly perceived this as to make 

 it the type of a new genus, which he named Thenea^ and thus 

 defined : — 



Fam. 3. Tethyad.^. 



Thenea. Sponge massive. 



Spicules : — 1. Simple, not ijrotruded beyond tlie surface. 



2. Large, furcate, teruate, with expanded long 



acute rays. 



3. Elongate, stellate, projecting beyond the 



surface. 

 Thenea vmricata, Bwk. ih. i. pp. 25, 108, figs. 35, 304, 305. Norway, 

 Vigten Isl. 



In this definition I recognize as correct the statement that 

 the sponge possesses acerate and bifurcate-ternate spicules 

 and elongate stellates — a collocation of forms so different from 

 that which obtains in any other sponge known in Gray's 

 time as to make the generic distinction founded on it a matter 

 beyond dispute. Moreover, lest it should be objected that 

 the genus rests on a MS. species, I would submit first tliat 

 Gray, by thus bringing together Bowerbank's scattered 

 references and figures, and by adding thereto, as further infor- 

 mation, the presence of acerate spicules, did virtually raise 

 Thenea muricata from the rank of a ]\IS. to that of a de- 

 scribed species ; and next, if this be not admitted as a matter 

 beyond question, that there is no reason why, upon occasion, 

 a genus should not be defined before a species. If the parti- 

 cular information which would enable us to define a species 

 be not forthcoming, while the general characters which are 

 available for generic distinction lie ready to hand, there can 

 be no reason, beyond a superstitious adherence to custom (not 

 recognized convention), which shall prevent us making good 

 use of them. Thenea^ therefore, is a well-grounded generic 

 title applicable to all such sponges as possess a spicular com- 

 plement like that defined in this connexion by Gray. 



Gray's definition is not unmixed truth ; thus, we know now, 

 in direct contradiction to Gray's statements, that the sponge 

 is not massive, that some of the acerate spicules do project 

 beyond the surface, and that the spinispirules do not*. Seri- 

 ous as these errors undoubtedly re, they are in no way fatal j 



* Or do so only iu dried specimens as a consequence of shrinking. 

 Ann. & Mag. N. Hist. Ser. 5. Vol. ix. 30 



