HIBEIiNACULA. 
?,11 
submerged iu the ocean, and that upon their upheaval the ({astropods 
now occu})ying these burrows merely appropriated them as convenient 
places of shelter, hut that the snails have themselves formed these 
rock-tunnels may, however, he almost couhdently assumed, not only 
because Helices, especially Helix ai^persa, are generally ahundant 
near the burrows and that living specimens are always found iu the 
Fig. 601. — Hibernncula or Rock-burrows formed by llelLx: aspcrsa Mull., discovered in the 
Great Ormes Head, North Wales, by Mr. R. D. Darbishire, H.A. (modified after Prof. Bonneyj. 
The vertical cliff had a north aspert ; the small detached fragment at base, though from a south 
aspect formed the roof of a horizontal fissure. 
freshest and least weathered tunnels, hut also from their characteristic 
(im'nding direction with the opening below, which clearly distinguishes 
these Ilelicidiau cavities from those of the marine boring mollusks, 
which usually follow a descending direction with the mouth of the 
tunnel opening ah(jve. 
