BARNACLES AND ACORN-SKELLS. 183 



There is a smaller species of Necked Barnacle (Scalpellum 

 vulgare), the shelly portion of which, seen edgeways, looks like 

 a penknife, whence the Latin name. It is usually found grow- 

 ing among corallines ; it is figured in accompanying group. 



PYRGOMA. SCALPELLUM. 



ACORN-SHELL. 



PORCATE-BARNACLE. 



There is a peculiar little Barnacle called Pyrgoma anglicum, 

 which is parasitical upon the pretty Devonshire Cup-coral 

 (Ca y yophyllia smithit). It is shown on the coral in the upper 

 left-hand side of our illustration above, and may be looked 

 for in any of the localities where this coral occurs. It attaches 

 itself to the outer edge of the plates of the corallum. 



Let us turn now to the more familiar Acorn-shells (Balanus 



