Another curious form closely related to this is the Keyhole Limpet,[26]
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 fœtid 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 ample ivory-like shells, which yet
cannot half contain the whiter flesh of their ampler bodies, and the
long stout yellow siphons that project from one extremity, reaching far
up the hole towards the surface of the rock.[27]
We lift one from its cavity, all helpless and unresisting, yet
manifesting its indignation at the untimely disturbance by successive
spasmodic contractions of these rough yellow siphons, each accompanied
with a forcible _jet d’eau_, a polite squirt of sea-water into our
face; while, at each contraction in length, the base swells out, till
the compressed valves of the sharp shell threaten to pierce through its
substance.
[Illustration: