In a paper which I communicated to the Geological Society of London, Nov. 21, 1866, (“On some points in the structure of the Xiphosura, having reference to their relationship with the Eurypterida”) I have recorded all the then known genera both of Xiphosura and of Eurypterida, and in the tables which accompany the first part of my Monograph on the Merostomata, I have given both the genera and species with their range in time and space.

Among the new Oolitic Crustacea to which I drew attention at the meeting of the British Association, Dundee, was a species of Prosopon from the Stonesfield Slate.

This genus was proposed by H. von Meyer, in 1835, for certain minute forms of crustacea from the Upper White Jura of Oerlinger Thal, and other localities in Germany, from whence he has described twenty-nine species, and in addition to these, one from the Lower Oolite, three from the Coral Rag, and one from the Neocomian (see Palœontographica, for December, 1860, vol. vii., p. 183, pl. xxii.)

Having described in some detail, the rocks of the Maentwrog, Festiniog, and Dolgelly groups, and given a list of the fossils found in each, I shall now make some general remarks upon the fauna. In Part I. I have mentioned that out of all the numerous Trilobites from the Lower Cambrian rocks, only two genera, Agnostus and Conocoryphe, have been found in higher strata. Strictly speaking, this is only true of Agnostus, which passes unchanged in type from the Menevian to the Caradoc strata. On the contrary, the species of Conocoryphe from the Lower Cambrian rocks are of essentially different type from those that have been placed in that genus from higher beds. The latter have, I believe, been referred to the genus Conocoryphe rather from superficial resemblances than from true affinity.

The states of semi-crystalline silica are so various, and so connected in their variety, that the best recent authorities have been content to group them all with quartz, giving to each only a few words of special notice; even the important chapters of Bischof describe rather their states of decomposition and transition than the minerals themselves. Nevertheless, as central types, five conditions of silica are definable, structurally, if not chemically, distinct; and forming true species: and in entering on any detailed examination of agatescent arrangements, it is quite necessary to define with precision these typical substances, and their relation to crystalline quartz.

The following notes on the Weathering of Rocks near the Sea, culled from my note-books, appear to be facts unobserved by the various writers on subaërial denudation. Those agents would seem to act differently near the sea than away from it, not only in the quantity of the work done but also on the colouring matter in the rocks.