228 PORINID.^. 



This name, liowever, had been previously (1850) appropri- 

 ated by D^Orbigny, and could not stand. In the mean- 

 while Busk, having only a fragment to deal with, had 

 made it an Onchopora. It then found a home in the 

 Anarthropora of Smitt, from which, however, it was 

 subsequently dislodged by Norman as an alien, and he 

 proposed for it the genus Tessaradoma. I most reluct- 

 antly disturb it once more ; but, as I can find no essential 

 distinction between the Tessaradoma of Norman and the 

 Porina of D'Orbigny, founded as early as 1851, I have no 

 choice but to refer it to the latter. Now that incrusting 

 species are admitted to the genus, Norman's name would, 

 in any case, be clearly inapplicable. 



The British form, indeed, has fewer rows of cells than 

 the species described in the 'Paleontologies' but their 

 mere number is a matter of no systematic importance ; 

 the difference between four and six or eight cannot 

 reasonably be made one of the criteria of a genus. The 

 point has no structural significance. In all essential 

 particulars Tessaradoma and Porina are identical. 



Unfortunately the change in the generic designation 

 involves the displacement of Sars's specific name for the 

 British form, as the Eschara gracilis, Lamk., is a Porina. 

 It becomes necessary, therefore, to adopt in its stead 

 Busk's name borealis, though it seems hardly right that 

 the discoverer of the species and the first to describe it 

 should have no direct part in it. I should gladly connect 

 his name with it did the laws of scientific nomenclature 

 permit. 



As to the union of P. tubulosa and P. borealis in one 

 genus, the cells of the two agree in all essential points ; 

 and, as I have already urged, there seems to be no suffi- 

 cient reason for creating genera merely to represent such 

 diftevences of habit as they exhibit. 



