Marvels of the Universe 831 
THE KEYHOLE LIMPETS AND THE ORMER SHELL. 
Noteworthy for the “‘slit’’ in the shell which allows for the passage of fresh sea-water and waste material to and from 
the shell. In the Ormer the slit develops into a series of perforations. 
peculiarity is still further developed in the neighbouring Egg Shell (5), where the outward semblance 
to a spire is completely lost, and the aperture is enlarged till it occupies the whole length of the 
shell. This shell is one of the Cowry family, and it is noteworthy that the race, in their early 
stages, develop normal, though small, spirals, which are swallowed up in the aggregation of the 
later whorls. 
Now let us examine the clasp shells on the lower part of the page. The variety is not so great 
as in the univalve shells, and is chiefly concerned with the position of the umbones, or beaks, situated 
near the hinge. The normal position for these is shown in the Scallop Shell (1), though its tendency to 
lean to one side, as in the Venus Shell (3), is very common. Sometimes a shell is so formed that one 
valve is out of all proportion to the other ; and when this happens, the beak of the larger valve is 
always very prominent, and curves towards the margin, while that of the smaller valve is merely 
rudimentary. This style of shell architecture reaches its highest fulfilment in the Lamp Shell (2), of 
which a fossil is shown on page 833, and becomes a perversion of all recognized ideas of bivalves in 
t 
Hippurites cornu-vaccinum. What the laws are which have governed these developments it is at 
TENT SHELLS. 
No. 1 is a Tooth Shell, which is probably a highly developed form of ‘a primitive “Tent,’’ such as the Umbrella (2). The 
Slipper Limpets (3 and 4) and the Cup-and-Saucer Limpet (7) show a more elaborate internal structure. The packing habit 
of the Slipper Limpets is shown in 5 and 6. 
