PALEONTOLOGICAL EECORD. 381 



■worms, Suctorial-worms, Round- worms, &c). We are, therefore, 

 without any geological evidence of the former existence of Scolecids; 

 though no doubt can be reasonably entertained but that the group 

 dates back to times long anterior to the present fauna. 



d. Annulosa : — Many of the lower Annulose animals, such as 

 Leeches, Earthworms, and Errant Annelides, possess no structure by 

 which we could expect to get direct evidence of their past existence. 

 The last of these, however, have left ample traces of their former 

 presence in the form of burrows or tracks upon the mud or sea-sand ; 

 and the so-called "Tubicolar" Annelides are well represented by 

 their investing tubes. In the case of the higher Annulosa another 

 law steps in to regulate their comparative abundance as fossils. Most 

 of the fossiliferous formations have been deposited in water, and of 

 necessity, therefore, most fossils are the remains of animals naturally 

 inhabiting water. As most deposits, also, are not only aqueous but 

 are further marine, most fossils are those referable to sea-animals. 

 It follows, therefore, that the remains of air-breathing animals, 

 whether these be terrestrial or aerial, can only be preserved in an 

 accidental manner, so to speak, as by falling or being blown into the 

 water ; except in the rare instances in which old land-surfaces have 

 been buried up by sediment and thus partially kept for our inspection. 

 In accordance with this law, the most abundant and important fossil 

 Annulose Animals are Crustaceans; for these are not only generally 

 aquatic in their habits, but are provided with a resisting shell or 

 " exoskeleton." The air-breathing classes of the Myriapods (Centi- 

 pedes and Millipedes), the Arachnida (Spiders and Scorpions) and the 

 Insscta or true Insects, on the other hand, have been much less com- 

 monly and completely preserved ; though many of them are perfectly 

 capable of being fossilised. Almost all such remains as we have, 

 however, of these three great classes are the remains of isolated 

 individuals which may have been accidentally drowned ; or else they 

 occur in hollow trees, or in fragments of ancient soils, or in vegetable 

 accumulations such as. coal and peat. There are, however, some 

 aquatic insects, and there are many insects the larvae of which 

 inhabit water ; and we have not infrequent instances of their occur- 

 ring as fossils. 



e. MoClusca: — This sub-kingdom requires little notice, since the 

 greater number of its members possess hard structures capable of 

 being readUy preserved in a fossil condition. Thus, the homy or 



