Vermes — Worms. 85 



It must therefore be remembered, when consulting the collection Worms. 



of fossil worms, that the names given to the specimens do not mean GAILEBY 



the same in palaeontology as they do in zoology. Thus, zoologists 



use the names Serpula and Bitrypa for worms which are closely 15a and 



allied to one another, but differ in the structure of the thorax. T*^^^" 



case 79. 

 Palaeontologists, however, are unable to use this character, as no 



fossil specimen known of either genus retains any trace of this 



part of the body, and the genera are separated only by the 



character of the tube. The meaning of some other names, such 



as Pomatoceras, Sahella, and Galeolaria, also depends on whether 



they are used for recent or fossil specimens. 



The tracks made by worms when Avalking over soft mud cannot 

 be distinguished from those of some other animals and of plants, 

 and the tracks are therefore all placed together in Wall-case 7 

 in Gallery XI. In spite of the elimination of these, it is 

 probable that the specimens exhibited in the worm collection 

 include remains of animals belonging to other groups. Some of 

 the burrows (such as those in the Aymestry Limestone) were 

 probably made by moUusca, and some others (such as Talpina from 

 the Chalk) by sponges. Some of the tubes, moreover, such as the 

 Vermetus from the London Clay and some species referred to 

 Bitrypa^ will probably have to be transferred to the Mollusca 

 if the bodies be ever found. The famous Spirorlis from the 

 Coal-measures of South Joggins, in Kova Scotia, is almost 

 certainly a mollusc. (Fig. 148, p. 87.) 



The fossil worms, therefore, are not a group which admit of 

 much precision in identification and classification, although they 

 are often of considerable value to the geologist as marking the age 

 of rocks, and the conditions under which they were formed. 



The Vermes are divided into several groups, of which, 

 however, with some doubtful exceptions, only one is met with 

 in the fossil state. This is the group Chaetopoda, or worms 

 bearing bristles, or "setae." Of this group there are two 

 divisions — the Oligochaeta, the members of which have only 

 a few "setae"; and the Polychaeta, in which the worms have 

 bundles of bristles, attached to lateral appendages known as 

 " parapodia." The Oligochaeta are not certainly known as fossils, 

 and the Polychaeta therefore include practically all the fossil 

 worms. The Polychaeta are divided among two orders — the 

 Errantia, or free-swimming worms ; and the Tubicola, including 



