Echini from the Palaeozoic formations are rare, and rarer still is it to find a new form of one of the more specialized genera in good condition of preservation. It was a keen pleasure to me, therefore, when my friend Dr. F. A. Bather, of the British Museum, recently gave me the privilege of studying and reporting on the specimen here described. It proves to be a species of the highly specialized genus Lepidesthes from the Lower Carboniferous, and was sent to Dr. Bather for study by the authorities of the Hancock Museum, Newcastle-on-Tyne.

The greatest diameter of a Pecten is nearly always the height. It is easier to visualize the size of a shell from this measurement than from the length. Consequently in tabulating the dimensions of the species the height is first given in millimetres, followed by the length as a percentage of the height. Since in the vast majority of the ordinary species the shell is, except for the auricles of the right valve, subequilateral, no obliquity measurement is necessary as with the Limidae. Another redundant measurement in dealing with Jurassic Pectinidae is the inflation. This dimension is always such a small percentage of the height that accuracy of measurement without special apparatus is a matter of difficulty unless both valves happen to be joined, closed, and free from matrix. Even such differences as do exist can rarely be detected in allied species, such as might be liable to confusion in other respects.

During the last two years a series of deep excavations have been made in the floor of the Aire valley near Skipton (on the border of sheets 92 S.E. and 92 S.W. 1 inch to 1 mile, Geological Survey). These have brought to light a hitherto unsuspected deposit of laminated clays of great thickness, which are of considerable interest in interpreting the events of the Glacial retreat in this valley. A. Jowett and H. B. Muff in 1904 published their work on the glaciation of the Aire valley between Keighley and Bradford, in the course of which they described three terminal moraines of the Aire glacier, at Tong Park, near Baildon, at Hirst Wood, about a mile and a half west of Shipley, and at Bingley; in the course of the paper they mention without comment the fact that above the Hirst Wood and Bingley moraines there is in each case an extensive flat of alluvial material, extending far up the valley. Although these have long been tacitly regarded as lake flats, the first confirmation was received in 1920 when the excavation of a deep trench in the flat half a mile west of the Hirst Wood moraine revealed a quantity of laminated clay underlying the undoubted river gravels. The excavation was only temporary, and unfortunately no measurements or deeper trials were obtained. Recently a trench above the Bingley moraine has been cut deep enough to show the laminated clay underlying the river gravels here as at Hirst Wood, and these two exposures have directed attention to the existence during late Glacial and post-Glacial times of a series of lakes held up by the terminal moraines left by the Airedale glacier. That such lakes existed has long been the opinion of most local geologists, but they have always been regarded as of brief duration, drainage being rapidly accomplished by breaching of the moraine barrier, or, in the Hirst Wood case, by super-deepening of the cut round the north end of the moraine, a cut probably initiated in late Glacial times. The material from the Skipton excavations indicates that these lakes were of far longer duration than previously suspected.