320 ANNULOSA. 



pliycus, &c., are really the filled-up burrows of wandering 

 marine worms, and all such remains may at present be 

 grouped together under the common name of Planolites. At 

 the same time, some fossils of a similar general appearance 

 and occurring in similar strata (Cruziana, for example) may 

 really be of vegetable origin, and these will be briefly noticed 

 later on. 



The fossils known as Lumlricaria, so abundant in the 

 Solenhofen slates (Jurassic), have, again, been generally re- 



rig. 191. Plauoliies vulgar is, the filled-up burrows of a marine worm. Upper 

 Silurian (Clinton Group), Canada. (Original.) 



garded as casts of the alimentary canal true " worm-casts " 

 in fact of marine worms ; and certainly they present every 

 appearance of these. They are stated, however, to consist 

 commonly of crystalline carbonate of lime, and this would 

 render their true nature doubtful. 



III. Trails and Tracks. Lastly, we have to deal with a 

 great group of fossils which have been supposed to be of the 

 nature of the " trails " of Errant Annelides that is to say, 

 markings formed by the animal dragging its soft body over 

 the surface of wet sand or mud, between tide-marks or in 



