1873.] Annelides of the Older Palaeozoic Rocks. 289 



different nature from the preceding, and may reasonably be compared to 

 the burrows of the recent lobworms. These burrows run more or less hori- 

 zontally as compared with the laminae of deposition, or they penetrate the 

 strata obliquely. They are not burrows of habitation, but are wandering 

 tunnels excavated by the worm in its search after food. The fossils of 

 this group, therefore, as preserved to us, are not the actual burrows 

 themselves, but the burrows filled up with the sand or mud which the 

 worm has passed through its alimentary canal. The burrows of this 

 kind (including many forms previously described under the names of 

 Chondrites, Palceophycus, &c), the author groups together under the 

 name of Planolites. 



The second great group of Annelide-remains comprises genuine 

 surface-trails or " tracks," which of necessity never pass below the surface 

 of the bed on which they occur. Some of these remains, such as 

 C rossojpodia, are, beyond doubt, due to the operation of marine Annelides ; 

 but it may be a matter of question whether we have in these cases the 

 actually petrified body of the worm, or merely the track produced by the 

 passage of the animal over the surface of the mud or sand. The author, 

 however, gives reasons for believing that the latter explanation is truly 

 the correct one. Other fossils belonging to this group (such as 

 Myrianites) are equally, beyond doubt, produced by the operations of 

 marine animals : but it remains quite uncertain whether they have been 

 formed by Annelides, Crustaceans, or Mollusks. Lastly, there are 

 remains which appear to be really casts of the surface-trails of Annelides 

 or other marine creatures, and which, therefore, are elevated above the 

 surface of the bed on which they occur. Such remains may readily be 

 confounded with those belonging to the genus Planolites, from which 

 they are only distinguishable by the fact that they are strictly confined to 

 a single surface of deposition. To fossils of this nature the author 

 proposes to restrict the generic title of Nemertites. 



Finally, the author describes some singular tracks apparently produced 

 by Crustaceans belonging to the genus Ceratiocaris, and for which he 

 proposes the generic name of Caridolites. 



The following list comprises the species of fossils described in this 

 communication : — 



A. Bukeows. 



I. Genus Arenicoeites, Salter. 



1. Arenicolites sparsus, Salter. 



2. didymus, Salter. 



3. robustus, Nicholson. 



II. Genus Scoeithes, Haldemanjjf. ^ 



4. Scolithus canadensis, Billings.. 



5. linearis, SaO* f^ch& C^&^°^ * 



6. verticalis, Hall. 



