Sponge-fauna of Norway. 431 



lacks tlie cortex which is essential to that genus ; on the 

 other hand, it agrees fundamentally with Thenea, and may be 

 called, at this stage of our argument, Thenea agariciformis. 



Again in 1870, December of that year, Mr. Saville Kent 

 (vii.) described quite independently a sponge in all respects 

 identical with that mentioned and labelled by O. Schmidt. 

 Kent's description is good and fully illustrated, perhaps a 

 little too fully, as he includes certain extraneous sexradiate 

 spicules as proper to the sponge, an error which he was the 

 first to correct (viii.). Kent named his sponge Dorvillia 

 agariciformiSj choosing, by a quite accidental coincidence, the 

 same character for specific designation as Schmidt had done 

 previously. According to the fortune which seems to wait 

 on nomenclature, we might therefore expect the species would 

 turn out to be different ; but, notwithstanding, they are cer- 

 tainly the same. 



In the note (viii.) which followed his first paper, Kent states 

 that Thenea WalUchn is an embryonic form of T. agarici- 

 formisj a view accepted by Wright and by spongologists 

 generally. Since, however, Wright's figures of the large few- 

 rayed stellates differ somewhat from those given by Kent, it 

 appeared to me that a loophole was left open for error ; and I 

 was led therefore to compare the type specimen of T. Wal- 

 lichii * with Kent's figures and witli mountings of the usual 

 agaric form. The result is to show, in a most satisfactory 

 manner, that no sort of real difference exists between the two 

 species : T. agaricformis is larger and has a well-marked 

 agaric form with a specialized poriferous area, while T. Wal- 

 Uchn is of a globular form and without an evidently specialized 

 poriferous area ; these trifling differences are unquestionably 

 due to a difterence in age. Though young. Professor Wright's 

 specimen is not embryonic — at least no more so than a child of 

 six is, compared with an adult man. It is considerably ad- 

 vanced in growth ; for my smallest specimens of young Thenea 

 WalUcliii measure only 0'0146 inch in diameter, and this is 

 0'075 inch, or more than five times as large across. 



As Wright's species is certainly a good one, and as it takes 

 precedence of Schmidt's by some three months, that of the 

 latter must, by the most fundamental rule of nomenclature, be 

 suppressed ; we then have 



Wyvilk-Thomsonia Wallic/m, Wriglit. 1 



Stelleita agaricifai-mis, 0. S. \ = Thenea Wallichii, Wright. 



Dorvillia affariciformis, Kent. ) 



* For the loan of this valuable type my thanks are due and heartily 

 tendered to Mr. C. Stewart and the Council of the Royal Microscopical 

 Society. 



30* 



