PALAEONTOLOGY. 12T 



INVERTEBKATA. 



Mollusca. Eemains of all those classes possessing in- 

 ternal or external shells are very abundant ; the 

 Tunicates being soft-bodied are alone unrepre- 

 sented. 



Annulosa. Of Insects, the skins, limbs, and wings 

 are occasionally found ; of Myriapoda and 

 Arachinda remains are very rare ; of Crustacea,. 

 the limbs and carapaces are found in abundance, 

 and from the earliest times. 



The Annelids are only known by the shells of 

 Tubicola, and by the tracks and burrows of other 

 orders. 



Annuloida. Echinoderms are frequent fossils, leaving 

 remains of their tests, stems, arms, or spines. 



Scolecida, having no hard parts, are quite un- 

 known. 



Ccelenterata. The Actinozoa present abundant remains 

 of their hard skeletons or corals ; but the Hy- 

 drozoa, being mostly soft-bodied, have left few 

 traces. 



Protozoa are chiefly represented by the spicules of 

 Sponge and the minute shells or tests of Fo- 

 raminifera. 



Since the majority of rocks composing the crust of 

 the earth are of aqueous and principally marine origin, 

 we should naturally expect the fossils which they con- 

 tain to be the remains of aquatic and principally marine 

 beings ; this at once accounts for the preponderance of 

 such forms in the above list as are commonly met with 

 in the fossil state. 



