362 BALANIDiE. 



This species comes so close to the last, that I am not sure 

 that I have acted rightly in retaining it, but I think that it 

 is distinct ; and in this case, it is the representative, on the 

 other side of the Atlantic, of P. Anglicum of our own side. It 

 will be sufficient to point out the few points of difference. 

 The shell is much more depressed, with the orifice oval, 

 larger, and not so narrow. It is apparently of a paler red, 

 and the radiating ribs perhaps not so prominent. The 

 basis offers the most important difference, being deeply 

 imbedded in the coral; and there is not the least appearance 

 of the thin shelly layer, of which it is composed, being 

 permeated by pores, as, Ave have seen, is always the case 

 with P. Anglicum. As in this latter species, the sheath 

 here depends freely. The opercular valves are closely 

 similar ; but in the scutum, the adductor ridge occupies a 

 rather more central position ; and in the tergum, the basal 

 margin is more inclined towards, or forms a greater angle 

 with, the spur : these differences, by themselves, I con- 

 sider quite insufficient to characterise a species ; but con- 

 joined with the flatter shell, the larger orifice, the more 

 deeply imbedded and non-porose basis, they may, I think, 

 be admitted as specific. In dimensions, this species seems 

 to attain a slightly larger size than P. Anglicum, for several 

 specimens were *22 of an inch in diameter. 



3. Pyrgoma cancellatum. PI. 12, fig. 5 a — 5/. 



Pyrgoua cancellata. Leach (!) Encyclop. Brit., Supplement, 



vol. 3, PI. 57, 1824. 

 — lob ata. /. E. Gray (!) Annals of Philosophy, (new 



series), vol. 10, 1825. 

 Cretjsia kayonnante. De Blainmlle. Diet. Sc. Nat. (sine des- 



cript.), PI. 11G, fig. 7, a, b. 



Shell icith the circumference generally lobed : scutum elon- 

 gated, with the adductor ridge descending far below the basal 

 margin, and produced at the rostral end into a square point ; 

 tergum. icith the spur four times as long as the upper part 

 of the valve. 



