FOSSIL SCORPIONS 69 
ages have been hunted extensively; they must 
always have had plenty of natural enemies anxious 
to prey upon them. 
4. Arachnida (Greek, arachné = spider). — Head 
and thorax joined, and covered with a carapace. 
Four pairs of walking legs. No proper feelers. 
Breathe by lung-sacs. Examples: Spiders, Mites, 
and. Scorpions. Spiders are familiar animals, and I 
shall not attempt to describe them. Scorpions 
have two pairs of limbs, one of them large and the 
other much smaller, ending in crablike nippers, 
which take the place of jaws. If you have learned 
some astronomy, you will bear in mind that one of 
the constellations was named by the ancients after 
the scorpion. There are fossil scorpions very 
similar to living species, and some of them have been 
wonderfully well preserved, so well that an un- 
skilled person having seen a modern specimen could 
not fail to know a fossil one. Up to the year 1884 
no land animal remains had been found in Silurian 
rocks, but in that year some fossil scorpions were 
discovered in Silurian strata of Scotland, the United 
States, and Sweden. If creatures so well advanced 
in the scale of life as scorpions existed in Silurian 
times there must then have been’a large variety of 
animal life, in spite of the fact that so few remains 
have been preserved. The Carboniferous rocks of 
Scotland have yielded great numbers of scorpions ; 
they may be found in the shales in excellent 
condition. 
Before passing on to the Mollusca, or the shell- 
fish proper, mention must be made of the Mot- 
LUSCOIDEA, which have soft, unsegmented bodies 
