On the 24th of June, 1885, a paper by me, entitled “Observations on some imperfectly known Madreporaria from the Cretaceous Formation of England,” was read at a meeting of the Geological Society which, encountering an adverse report from the referee, was with the consent of the Council, withdrawn by me, and published verbatim in the Geological Magazine of the same year (Dec. III, Vol. II, pp. 541–563, PI. XIV), 1885. The present communication is a continuation as well as a correction of the former one, which has become necessary from the acquisition of additional material.

My attention has recently been called to some very interesting comments on the problem of the delimitation of the Silurian and Devonian systems, which were made by Dr. Elles in her Presidential address to Section C of the British Association at Liverpool. I am so heartily in agreement with all the principles of the modern classification of strata, as laid down by Dr. Elles, that it seems of advantage to recall very briefly how closely these principles are adhered to in using the Ludlow Bone-bed as the local base of the Devonian in England.

The following note is based on two papers by Professor A. G. Nathorst and on further details which he has kindly communicated by letter. For the loan of the block (Fig. 1) thanks are due to Dr. H. Munthe, Secretary of Geologiska Föreningen i Stockholm.

By the term ‘collodion imprint’ is meant the impression of any surface on a thin film of collodion. Such an impression is obtained by letting a drop or two of collodion dissolved in ether fall on the surface to be copied. The ether evaporates rapidly, so that in two or three minutes the film is hard. If it does not of its own accord come loose at the corners, it is easily raised by a needle or sharp knife. It is then lifted on to a glass microscope-slide and preserved dry under a cover-slip held in position by gummed strips of paper or by Canada balsam. When the imprint is very sharp, the film can, if desired, be preserved in glycerine-jelly without its distinctness being greatly affected. Some films may be less successful than others, and some may curl too much, so that it is as well to take more than one imprint. In any case it is advisable to throw away the first made, since it usually retains some dust from the surface of the object, whereas following films will be free from this. If the collodion solution is too thick it may be thinned by the addition of ether or of ether and alcohol.

After a recent visit to Trinidad I am led to add my testimony to that of the numerous observers, who for more than a hundred years have written concerning this remarkable phenomenon.

The skeleton figured on Plate XII is that of a small Pliosaur, Peloneustes philarchus, Seeley, sp. This specimen was obtained from the Oxford Clay in the neighbourhood of Peterborough by Mr. A. N. Leeds, F.G.S., to whom the British Museum is indebted for a great series of more or less perfect skeletons of many species of Oxford Clay Reptiles, including the beautifully preserved and nearly complete examples of Cryptocleidus oxoniensis and the remains of Cetiosaurus leedsi, now mounted in the Gallery of Fossil Reptiles. So far as I am aware, this is the first skeleton of a Pliosaur that has been mounted so as to show the true form of the body in those reptiles. All the bones belong to a single individual, but the left-hand paddle and the distal portion of the other paddles being wanting, they have been represented by plaster models made from the paddles of another individual, which are exhibited on the floor of the case. The left ischium has been modelled from that of the opposite side.

In commencing a new volume the Editors desire to convey their thanks for the generous support they have received during the past year from contributors and subscribers. They still, however, find themselves faced with financial difficulties of a serious nature, arising from the continued increase in the cost of production, For the first half of 1920 a small profit was made, but this was almost wiped oyt by a considerable further rise in the cost of printing in the middle of the year. An important item in expenses is the cost of plates, and they are regretfully compelled to inform their contributors that it will under persent conditions be impossible to produce plates at the expense of the magazine. They feel sure, however, that their friends will not hesitate to incur the expense involved in meeting the cost of the illustrations, which are so voluntarily in the past, and the editors trust that even under the present conditions, that bear so heavily on people of moderate means, they will be able to continue to provide them.