PHOLAS HOLES. 53 



Another curious form closely related to this is the 

 Keyhole Limpet, 1 whose shell is of a long oval outline, 

 of a lower cone, reticulated, like the Slit Limpet, but 

 pierced at the summit with a double hole, or rather a 

 perforation apparently made of two holes broken into 

 one, something like a keyhole. This orifice, like the 

 slit in the former case, is for the discharge of the effete 

 water taken in in breathing. 



See ! here is the soft red sandstone lying in great 

 beds, pierced through and through with smooth round 

 holes, just as if bored with a carpenter's auger, big 

 enough to admit a man's thumb. What agency has 

 been in operation to effect these perforations ? Let us 

 try to discover. 



A few good blows with the stout hammer on the 

 chisel-head serve to split off a great slice of the coarse 

 red sandstone. The holes run through its substance, 

 but they are all empty, or filled only with the black 

 foetid mud which the sea has deposited in their cavities. 

 Yes ; these are too superficial ; they are all deserted ; 

 the stone lies too high above low-water mark : we must 

 seek a lower level Try here ; where the lowest spring- 

 tide only just leaves the rock bare. Ha ! now we have 

 uncovered the operators. Here lie, snugly ensconced 

 within the tubular perforations, great mollusca, with 



1 Fissurella reticulala. 



