34 RELICS OF PRIMEVAL LIFE 



It would thus seem that for some unknown reason 

 the highest and lowest Mollusks may have been lo- 

 cally plentiful, but the intermediate types were rare. 



The much lower group of Echinoderms, or Sea- 

 urchins and Sea-stars, curiously enough puts in but 

 a small appearance in the Early Cambrian, being 

 represented, as far as yet known, by only one 

 embryonic group, the Cystideans. A little later, 

 however, Feather-stars became greatly abundant, 

 and a little later still the true Star-fishes and 

 Urchins. The aberrant group of the Sea-slugs seems, 

 so far as known, to be of more modern origin ; but 

 most of these animals are soft-bodied, and little 

 likely to have been preserved. 



The great group of the coral animals, so marked 

 a feature of later ages, is scarcely known in the 

 oldest Cambrian, except by some highly generalized 

 forms ^ (Fig. 5). There are, however, small Zoophytes 

 referable to the lower type of Hydroids, and mark- 

 ings which are supposed to be casts of stranded 



^ Dr. G. J. Hinde has carefully studied these forms, and also 

 similar species occurring in Lower Cambrian beds in different 

 parts of North America, Spain, Sardinia, and elsewhere. See 

 note in the Appendix, and Journal Geol. Society of Londo?i, 

 vol. xlv. p. 125. 



