184 PROF. T, M‘KENNY HUGHES ON SOME TRACKS OF 
some varieties of the beetle-tracks, especially those of land-beetles, 
strongly approach Wereztes and Myrianites. 
I have noticed above the occurrence of marks produced by worms - 
and grubs in relief on the surface of the mud; another curious 
example I may also give. In some cases in the footprint of a frog 
the line of the toes is marked in relief (Pl. XI. fig. 5), not depressed, 
as one would naturally expect, on the upper surface of the mud. 
This appears to happen where the mud has just that consistency, 
which causes it to stick to that part of the foot which is well 
pressed into it, and which, on being withdrawn, lifts it up, as a 
spoon or finger draws up after it a column of treacle or honey. 
When a night’s frost catches the wet surface of the mud, the 
most beautiful sprays of ice-crystals grow from the margin and 
from each projecting stick or stone. The water crystallizes out free 
from impurities, and needles of ice shoot through the mud in all 
directions. If a morning succeeds which is favourable to rapid 
evaporation, the ice evaporates directly, or the drying of the mud 
goes on fast enough to preserve the casts of the groups of ice- 
crystals. These are extremely difficult to procure, as the surface so 
scored readily cracks up and is not easily removed. The curious 
plume-like markings shown on. Pl. X. figs. 1 & 2 represent the 
frost-pattern on the mud, but give only a poor idea of what they 
are when fresh. 
Nathorst, in the valuable work referred to above, does not, of 
course, put forward as the result of his observations, that there were 
on the shores of the early Cambrian Sea the very same species of 
Crustacea as those he selected for his experiments, nor would I 
suggest that the Cruziania was the track of Melolontha vulgaris ; 
but I quite agree with him that from the analogy of these recent 
forms it is most probable that Cruziana, Nereites, Crossopodia, 
Palceochorda, and all that class of fossils are mere tracks, and do not 
represent either marine vegetation, as has been suggested in expla- 
nation of Cruziana, or the impression of the actual body of ciliated 
worms, as supposed by some in the case of WVerettes. 
EXPLANATION OF PLATES VIII.-XI. 
Puate VIII. 
Figs. 1 & la. Track of Water-beetle (Dytiscus &c.), showing variation in 
track as the animal passed from the more slimy part at A to the 
firmer mud at D. 
Fig. 2. Track probably of a Myriopod: compare with Pl. IX. fig. 4. 
Puate IX. 
Fig. 1. Track of Lithobius or similar form, crossing tube formed by bur- 
rowing animal. 
2. Track made by large fly? 
3. Track of burrowing animal. 
4, Track of Lithobius forcipatus, showing the marks made by the feet at 
one end of the track, a smooth trail in the softer slime, and the 
animal itself at the other end. 
