78 GUIDE TO THE FOSSIL INVEETEBHATE ANIMALS. 
Gallery 
VIII. 
Table-case 
26. 
Wall-case 
15 A. 
SaUcrdla and Arenicolites Irom the Ba.sal Quartzites of Lower 
Cambrian age in Sutherland. All these are .su])posed to 
liave been wonn-hurrows like those of the living lob-worm 
Arcnicola, but they may e([ually well have been made by 
})lant-ro(jts. Some supposed tubes of Serp^ilites from the 
same Quartzites have a slightly better claim to an annelid 
origin. On the top shelf of the Wall-case is another Areni- 
colites from the Upper Cambrian of Wisconsin ; in this the 
burrows are seen to stop short at tlie level of successive 
layers of rock, as though the animals had been killed off, 
either by a period of drought or by tlie sudden deposition of 
a thick coating of sand. With this compare the burrows in 
b c 
Fig. 35. — The tubicolous polychsete Ortonia. a, Ortoiiin intcrvwdia, 
from the Devonian of Canada : b, 0. conica, adhering to a hrachiopod 
shell, from the Ordovician (natural size) ; c, a single tube of the same, 
enlarged (after Nicholson). 
Wall -case 
15A. 
Table-case 
26. 
Wall-case 
15 a. 
Carboniferous sandstone from Calderwood Glen. A similar 
form called Seolithus comes from the Totsdam Sandstone of 
the same age near Ottawa ; the bit of rock exhibited on the 
bottom slope of the Wall-case shows over 80 burrows on a 
surface no bigger than a man’s hand. 
Among British Silurian specimens may be noted the 
lare'e Serpulites longisshnus, ot which a tube cur^ed in an 
almost complete circle is at the back of the W all-case, the 
small coiled SpirorUs (Fig. 3G), and the ringed tubes of 
Cornulites often found in clusters. The similar tiibes ot 
Ortonia are attached to shells and such-like objects (hig. 
From the Lower Devonian of Cornwall come some peculiar 
