So much confusion has occurred in the past over the identification of the genera which we have been discussing, that a list of some figured species from the Jurassic rocks, arranged in their proper sub-genera, may be useful. The only previous attempt at a list of this sort, so far as I am aware, is that by Professor Rollier, who was only able to enumerate five species. He called all these Beushausenia, but two are not Beushausenias but true Parallelodons, while a third belongs to a different genus.

The compressed angustumbilicate oxycones of the Deiran and Raasayan stages of the Lower Lias are generally assumed to be “homoeomorphous terminals of different lineages” of the Arietidae. But while the characters of the adult sutures of these forms link them with that family, there is comparatively little evidence as to the details of the ontogenetic developments of the various genera hitherto recognized. It is the purpose of this paper to repair this deficiency in some slight measure. The two forms selected, partially for convenience, are of considerably different ages: Victoriceras is a Raasayan form, while Oxynoticeras oxynotum occurs at a considerably lower horizon in the Deiran.

The suite of volcanic and metamorphic rocks described in this paper were collected by the writer in the early part of 1929. With the exception of the micaceous slate (Pl. XVIII, Fig. 3), which was found in situ along the valley of the Rio Patate near Guadaloupe, all the specimens were obtained near the Cascada de Agoyan, a locality a few miles downstream from Baños along the Rio Pastaza.

With certain well-known exceptions, ancient sandy and clayey sediments do little more than approach a condition of uniform grain-size. The so-called clays, silts and sands, and their consolidated equivalents, the mudstones, shales, silt-stones and sandstones, receive their appellation in most cases from the dominant grade present. Actually they consist of a mixture of particles, distributed over a considerable range of grain-size, in which the dominant grade, especially in the case of the finer deposits, often amounts to less than 50 per cent of the whole.