280 NOVEMBER. 



shells and small pebbles being incrusted with crowded 

 colonies of the commonest Acorn Barnacle. 1 We see 

 the same species, by tens of thousands, covering roods 

 and roods of the seaward surfaces of our rough rocks 

 between tide-marks. They rarely exceed one-third 

 of an inch in diameter at base ; but there is a much 

 more massive kind, rough with ridges and furrows, 

 and hence called porcate, occasionally found adhering 

 to the jutting angles of rocks hereabout, and much 

 more commonly on the coast of South Wales, around 

 Tenby. 



These Acorn Barnacles have no foot-stalk, but adhere 

 by the whole broad base to the rock or shell, on which 

 a floor either of strong stone, or of thin membrane is 

 formed, and from whose margin the stony plates arise, 

 enclosing a more or less conical chamber, with an orifice 

 at the summit. If we look in at this during the life of 

 the animal, we discern, a little below the rim, some 

 angular valves, which meet with a straight suture, and 

 close the interior. These are moveable, however ; and 

 under water they open like folding-doors, and a hand 

 of many fingers, each composed of many joints, modelled 

 on the same plan as that of the Scalpellum, but less 



1 Balanus balanoides, of which a gnnip is seen in the extreme left of the 

 foreground in Plate xxxi. ; B, porcatus, a single specimen, is a little to 

 the right. 



