Summary: In the preceding pages I have described 55 different forms of jaws, of which there are 33 from the Cincinnati group, 13 from the Niagara and Clinton group, 7 from the Hamilton group, of the Canadian rocks, and 2 from the Lower Carboniferous in Scotland. The respective numbers included under the different genera are as follows:— Eunicites 14 forms, Œnonites 10, Arabellites 19, Staurocephalites 1, Lumbinconereites 4, Nereidavus 1, Glycerites 3, whilst 3 forms are not referred to any genus. Of many of the forms there are numerous examples, whilst others are represented only as single specimens. Whilst there is thus shown a predominance of forms belonging to the genera Eunicites, Œnonites , and Arabellites (on account of the number and variety of the different jaws in the individuals of these genera, which renders the work of classification to a certain extent doubtful), no definite conclusions can be drawn as to the relative abundance of the different genera. It is quite possible that the number of species represented may be less than half the number of forms to which I have given names and descriptions, and they will therefore have to be accepted more for palæontological reference than as indicating so many separate species of these Annelids. It is possible that future discovery will bring to light some of these fossil Annelids with their jaw-plates in their respective positions, which will enable many of the forms described to be placed under a single species; in the mean time I have thought that it would be of interest to geologists to show, what had previously been inferred from the trails and markings, that Errant Annelids were very abundant in the Palæozoic rocks, and that, judging from their jaws, many of them were closely related to existing forms.