Chap. IX.] 
LOWER SILURIAN ANNELIDES ETC. 
201 
Annelides, or Sea-worms, we have already seen, Chap. LT., prevailed in some 
of the earliest sediments in which traces of organic remains are found*. They 
were not less plentiful in succeeding periods of the Silurian epoch, and occurred 
both in the form of burrows in the strata (Scolites), and as tracks upon the sur- 
face (Helminthites &c). It is scarcely doubtful that some of the long sinuous 
tracks observable on these old sediments were made by wandering species of 
this tribe ; but the idea has nevertheless been suggested by Geinitz, that some 
of those usually called Nereites may be soft and fleshy forms of Graptolithina, 
and therefore have no real affinity with the Annelides. Certain branched forms 
found in the old rocks of Thuringia, and described by Prof. Richter, give con- 
siderable force to this suggestion. Burrowing Crustacea also form such markingsf. 
Specimens of these tracks were figured, as previously stated, from Llampeter, 
in South "Wales, where they occur in strata which have been shown to overlie 
the Llandeilo rocks (see p. 72) : e. g., Nereites Cambrensis, Foss. 44. f. 3 ; N. 
Sedgwicki, f. 2 j and Myrianites MacLeayi, f. 1. 
Another form of these creatures, Crossopodia Scotica, f. 4, is given from spe- 
cimens collected by Professor Sedgwick, in the Graptolitic schists near Moffat, 
in Dumfriesshire, a locality which I have also examined, and where I found 
other species of these supposed long Sea-worms. The length of some of these 
creatures must have been prodigious, probably many yards, judging from the 
frequent parallel coils which are exhibited on the surface of the schists. (The 
annexed figures are very much reduced.) It should, however, be borne in mind 
that in many cases we see only the track of the Worm, and not the impression 
Fossils (44). Track-markings, produced by Annelides &c. % 
2 
1. Myrianites Mac- 
Leayi, Sil. Sysfc. 2. 
Nereites Sedgwicki, ib. 
3. N. Cambrensis, ib. 
4. Crossopodia Scotica, 
M'Coy. (All much re- 
duced in size.) 
Tracks of Sea- worms, 
and probably of other 
animals, in fine muddy 
sediments, now altered 
into slates. South Scot- 
land and Wales. 
of its soft body, which could rarely be preserved. Such tracks as these are met 
with in all the Palaeozoic rocks ; but the burrows of the Worms (Scolites and 
Arenicolites) are yet more frequent. Wherever the sediments are sandy 
these creatures seem to have been present ; and the markings generally at- 
tributed to Fucoids are for the most part only the filled-up burrows of marine 
Worms and other animals. 
* See Quart. J ourn. G-eol. Soc. vol. xii. p. 246 ; 
& vol. xiii. p. 199. 
t It is to be remembered that, according to 
Mr. Albany Hancock and other naturalists, such 
markings as these so-called Worm-tracks are in 
many cases caused by the burrowing of Crus- 
taceans beneath the sandy surfaces, — the galleries 
thus formed falling in, and producing furrow-like 
markings, with or without transverse notehings or 
lateral marks caused by the j erking advance of 
the burrower. Professor Dana (' Manual of Ge- 
ology ') and Professor Eupert Jones (' Geologist ') 
refer the Canadian Climactichnites to the burrow- 
ing of Trilobites; and Principal Dawson finds 
somewhat similar markings produced by the Li- 
mulus ('Canad. Geol. & Nat.'). See also Prof. 
Nicol's remarks on little borings at Durness, above, 
p. 166, note. 
I See Sil. Syst. pp. 363, 669, &c. 
