232 PORINID.E. 



tion between it and the depressed body of the cell. 

 Avicularia are wholly wanting*. 



Genus ANARTHROPORA (part.), Smitt. 



Der. From dvap9poe, unjointed, and iropos, an opening. 

 LF.PRALIA (part.), Busk. 



GENERIC CHARACTER. ZO<ECIA with the oral extremity 

 slightly produced and free, subtubular ; orifice terminal, 

 semicircular ; an avicularian pore on the elevated portion 

 of the cell in front ; special pore wanting. ZOARIUM (in 

 the British species) adnate. 



SMITT has united A. monodon with the two species of 

 Porina in one genus. But the more I have examined the 

 former, the less I have been inclined to adopt this course. 

 It seems to exhibit points of divergence from the latter 

 forms, which make it convenient to mark it off by a sepa- 

 rate generic designation. We are not, of course, to 

 understand by genera hardly- defined isolated provinces : 

 such, indeed, it would be difficult to find. They merely 

 represent phases or modifications, more or less marked, 

 of the family type, and are set apart to indicate in a 

 striking way its chief morphological variations. In 

 framing them we do not look for hard-and-fast lines : 

 they just as often suggest affinities as mark differences ; 

 they are simply landmarks in the morphological history 

 of a tribe. The present form seems to me to have quite 

 enough individuality to separate it from Porina. 



The orifice in A. monodon is semicircular, instead of 

 orbicular as in the latter. The shape indeed is affected 



* Smitt, indeed, has figured a specimen with avicularia, obtained by Pour- 

 tnlea off the coast* of Florida (Flor. Bryoz. pt. ii. pi. vi. fig. 141), which he 

 refers to thig form ; but I have little doubt that it is really a young colony 

 of Anarthropora monodon. 



