42 FURTHER REMARKS ON A LARGE FOSSIL MARINE WORM. 



But there is a well known species of another class — the earthworm^ to which 

 it seems to bear some analogy; it is asetigerous, so are they; it has no developed 

 head, the earthworms have not; it even appears, like the earthworm, to burrow, 

 as it sometimes dips through the stratum, and can be traced some little distance, 

 as if it had been burying itself in the mud — (not, however, like the Annelides 

 of the Dorsibranchiate order, who bury half their bodies in a permanent tube,) 

 probably not to any great depth, as there are no marks of holes burrowed in 

 the strata, and the greater part of the body is always found on the sm*face 

 of them; very few are found dipping through the strata. 



The only fossil Annelides which appear to have been much noticed are those 

 found in the lower Silurian flagstones at Lampeter. There are three or four 

 species, one or two allied to the Gordius; one named by Mr. Mc'Leay, Nemertites 

 OUivaixtii; the last has the most, but none of them bear much, resemblance to 

 the Annelide of the Carboniferous system. They are small, the largest is not 

 thicker than a quill, and appear to have been flattened, or else are only markings; 

 they are also, at least one is, setigerous — 'the others appear to be so; the setae 

 of the first are very well marked, but, at the same time, the articulations in 

 all are exceedingly imperfect. The Annelide of the Carboniferous system has, 

 on the contrary, the articulations very clearly marked — the setae not at all; 

 (nor is it probable there were any, because, if the Silurian rocks retained the 

 impression, it is likely that the Carboniferous would also;) the breadth is five 

 times greater than that of the largest Silurian; of the length, nothing can be 

 asserted of either. 



During the time when these Spiled up layers of tombs' were first deposited, 

 at the close of the Devonian period, the whole region must have been grad- 

 ually sinking; in some places masses of coral had already been formed and 

 submerged, constituting the floor Of the then sea; some obstacle had then arisen 

 — some change taken place in the flow of the current, or in the mouth of some 

 large river, and so a sand bank had been formed, which increased faster than 

 the bottom of the sea sunk. It rose to the level of the water^ a little above 

 it perhaps, at lowtide; it then became replete with life, and the worm, now 

 found fossil, not being capable of swimming, crawled over the sand at ebb tide, 

 and perhaps buried itself in it as the tide returned; but the bank, not being 

 raised above the sea level, of course sunk with the sinking land, and as it 

 sunk, one layer of sand was laid upon another, keeping its surface still at the 

 same level, while it gradually increased in thickness. The Annelides, few at 

 first, (for they ate found, though rarely, in the lower beds,) gradually increased, 

 owing their destruction to the submergence of the bank, or to the fresh water 

 brought down by some large river during the annual inundations — afresh water 

 acting like poison upon Marine Annelides.* The gradual sinking of the bottom 

 of the sea would, imperceptibly, change the zoology of the region; and the bank 

 having become submerged, the superincumbent strata would have been laid 

 upon it, to the depth of many hundred feet; and that sea shore, over whose 

 * Repoi'ts on Zoologj-. Eay Society, 1844, page 504. 



