A developmental sequence of Membraniporellæ showing progressive subordination of the ribbed front wall to a solid secondary front wall can be traced fairly directly from Membraniporella pustulosa, Bryd., which is prevalent in the zone of M. cor-anguinum and the Uintaerinus band and seems to die out in the zone of Marsupites. In the zone (restricted) of A. quadratus it is succeeded by

Membraniporella thoraciformis, sp. nov. (PL IX, Figs. 1–3.)

Zoarium unilaminate, incrusting.

The Iguanodon has been known since 1825, when the genus was first described from teeth by Mantell. Odd bones and various associated portions of the skeleton have been found in England, and in 1878 the skeletons of many individuals were discovered in the Wealden of Bernissart, near Mons, Belgium.

Almost due west of Mozambique Island, at a distance of about forty-two miles from the sea, the military road from Mosuril to Nampula crosses the Ampwihi River, an important tributary of the Monapo. During the dry season the stream is reduced to a string of stagnant pools, separated by long reaches of sand and gravel that here and there are interrupted by outcrops of the underlying formations. Throughout the greater part of its course the Ampwihi flows through a region in which gneisses persist with monotonous regularity, the only variation being that due to occasional intrusions of granite and of still later pegmatite dykes. At the point where the military road crosses the narrow channel a welcome diversion is introduced by the presence of a dark compact dyke about 10 feet in thickness. The dyke appears on the right-hand bank and crosses obliquely to the other side, taking a N.N.W.–S.S.E. course across the strike of the older rocks. Upstream, about seventy yards to the south-east, the Ampwihi bends to the south-west, so that it returns towards the dyke, which is again exposed across its sandy floor. The dyke was traced by Mr. E. J. Wayland in July, 1911, for a distance of altogether 200 yards, and was examined by Mr. D. Alex. Wray and later by myself during the same year. It is clearly the latest rock of the district, and is intruded along a line of fault, for in two cases pegmatite dykes seen on the eastern side are broken across and reappear on the western side with a well-marked northerly displacement.

There are many features characterizing the surface portions of deposits which are very puzzling. Indeed, the more one studies them the less one is inclined to be dogmatic. Many true glacial deposits show remarkable signs of disturbance throughout their mass. We may instance the Contorted Clay of Norfolk as a case in point. Even when boulder-clays are too uniform in texture to show signs of movement they are often kneaded into the rocks upon which they rest, and rocks of all ages often show such disturbances when they have been overridden by ice. Here we are dealing with the results produced by the action of forces operating from without the deposit.

During the past seven years I have published several papers based upon preliminary investigations on the anatomy of the Holectypoida, an order of the Euechinoidea which, by general consent, is regarded as transitional between the Regular and Irregular sections of the class. Continued study, aided by increased mental and technical experience, has revealed an ever-increasing number of interesting features in the order, and has made possible more definite and confident surmises as to its affinities with other groups. The series of contributions here commenced is intended to amplify, and in some cases to correct, the statements made in my earlier papers. With very few exceptions the actual descriptions that are given in the former work still seem to be essentially correct, but every fresh examination, even of the same specimens, testifies to the incompleteness of most of the observations hitherto published. New material, better or differently preserved, often draws attention to features overlooked or discarded as unimportant in the examples already studied. No apology is needed for the publication of incomplete descriptions of natural objects, since complete knowledge is as yet nowhere attained. When inaccuracies of observation have been detected, their nature and cause will be stated frankly, accompanied, verbally or not, by suitable contrition.

In working through the literature of Cretaceous Cribrimorph Polyzoa, it has been found necessary to determine the significance of the genera under which the different Cretaceous species have been placed by various authors, and, consequently, the genotypes of these genera. In several cases where a genus has been founded upon more than one species, apparently no subsequent author has definitely chosen a genolectotype from the several genosyntypes at his disposal; it has, therefore, seemed desirable to publish a list of certain genera under which various authors have placed Cretaceous Cribrimorph forms, namely those of which the genotype is or has been in doubt. It is hoped thus to simplify the work of future authors and to reduce to less confusion the somewhat chaotic use of certain names.