Zoœcia separated by a distinct furrow, which passes into a deep crevice at the junction points, widely rounded below but tapering very considerably and almost to a point above, with areas of the same shape and upright rounded side walls thickening considerably below, and often developing something of an internal front wall; average length of area 28 mm., breadth 2 mm., but marginal zoœcia often run much larger.

During the preparation and arrangement of a series of Lovenia forbesi from the Australian Miocene (presented to the Geological Department by Professor F. J. Cole), a peculiar interambulacral structure was displayed. Two of the specimens are severely weathered, with the result that their surfaces are smooth (except for the areolæ of the large tubercles), while the sutures are clearly outlined in dark brown across the pale background of the plates. In this way there is revealed the surprising fact that plate-crushing and resorption, of a type similar to that often found in Echinoid ambulacra, occur in four of the interambulacral areas. There is no corresponding development in the ambulacra.

On account of the aid it has given, palæontology has been termed the handmaiden of stratigraphy, but up to the present time petrology has not been called upon, so far as it might have been, to fulfil its appropriate duty towards the elucidation of the problems of stratigraphical geology and palæogeography.

At about 55 miles we reach the Hendon Lobe fan. At Dollis Hill the base of the fluvio-glacial beds lies at a height of about 200 feet, whilst their upper limit at Hendon is about 280 feet. On Finchley Hill to the north-east the Boulder-clay lies between the levels of 240 and 340 feet. This was a small lobe, and the fluvio-glacial fan may have sloped rapidly towards the fluvio-glacial gravels of the main stream. On the section, Fig. 2, the heights are shown without correction for slope towards the River Thames.

The triangular non-perforated areas lying on each side of the glabella and bounded in front and laterally by the fringe are usually described as the cheeks and distinct from the fringe, as if they alone corresponded to the fixed cheeks of the Opisthoparia and Proparia, or even included also the free cheeks of these orders. But if the facial suture is marginal, and if the lower plate of the fringe is considered to represent the free-cheeks, as Beecher maintained, the upper plate of the fringe must be regarded as merely a modified marginal portion of the fixed cheeks, so that the triangular areas within the fringe would only constitute the inner part of the fixed cheeks.