ON CERTAIN VERMIFORM FOSSILS. 19 



niiig from end to end; it is occasionally several feet in length, 

 winding in a very intricate manner, and is frequently and irre- 

 gularly convoluted, forming, as it were, loose knots or systems 

 in which neither the commencement nor the termination can 

 be easily detected, and which are usually connected together 

 by lengthened, slightly undulated portions of the track. The 

 windings are for the most part well rounded, and in their course 

 occasionally, but rarely exhibit inconspicuous, arched, transverse 

 ridges (c). The tracks also occasionally show enlargements 

 placed at some little distance from each other (fig. 2, a). When 

 this is the case there is no median groove. Another variety 

 occurs, but not frequently, in which there is neither groove nor 

 nodulous enlargements. The extent and complication of the 

 windings vary considerably ; and though they are for the most 

 part exceedingly intricate, as above described, they are at times 

 found of much less extent and comparatively simple, so that 

 they can be followed easily enough throughout their sinuosities. 

 At other times they may be seen, as it were, entirely unravelled, 

 running a considerable distance in an undeviating, or only 

 slightly tortuous lin§. 



Besides the above, another kind of track, also very abundant, 

 is found on our shores. It is, however, very different in charac- 

 ter, and is much smaller. It (PL IV. fig. 1) is in the form of a 

 narrow, wedge-shaped furrow (a), about two-tenths of an inch 

 wide, with the margins occasionally a little elevated (b, h). Its 

 windings are very capricious, irregularly rounded, frequently 

 abruptly angulated, and sometimes for a considerable distance 

 finely and regularly undulated or zig-zagged (fig. 2). This 

 species is often found in close proximity to the broad fo7^m pre- 

 viously described ; but occasionally it occurs high up on the 

 beach, and in pools and small hollows between the ripple-ridges. 

 In such situations, however, it is not confined to the bottom of 

 the hollows, but likewise passes up the sides of the bordering 

 ridges. 



A third variety (fig. 3) is occasionally seen, much resembling 

 the last both in size anjd windings ; but the furroAV (/:>) is smaller 



