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Show 4 PROF. G. B. HOWES ON THE SKELETON AND [Jan. 18, there came under my notice a short paper by Traquair (26, p. 143), in which he describes the restoration of parts of the tail of Protopterus. Finding that he had discovered certain irregularities in the skeletal elements of the said restored tails, and knowing that Haswell had recorded (15) some irregularities of the Ceratodus paired fins, it occurred to me that the same determining cause might have been at work in the two cases-i.e., that Haswell's "branching" fins might perchance be "restored" ones, like Traquair's. I was soon undeceived ; for, apart from Haswell's paper, I have had the good fortune to examine one such fin, sent by him to Prof. Huxley. The deductions arrived at in the sequel have arisen out of a study of it and of the fins of five other individuals. Three of them were kindly lent me by my master, Prof. Huxley ; of the two which remain, one forms part of our teaching-collection at South Kensington ; for the loan of the other I am indebted to m y Demonstrator, Mr. M . F. Woodward. It is remarkable that Gunther, in his Monograph on Ceratodus (14), does not mention Traquair's discovery already alluded to. It is clear that that author's paper must have escaped him, as I fail to find note of it under either " Pisces " or " Ganoidei," as reported by him for the ' Zoological Record' during both its year of publication and the succeeding one. The structural plan of the fin of Ceratodus is too familiar to merit detailed description here. Huxley has described (19, p. 46 et seq.) its general features with exceeding care, and I shall, in accordance with his system, speak of the segments of the axis as " mesomeres." The lateral rays will be described, under the same nomenclature, as parameres ; those which look dorsally when the fin is placed against the side wall of the body (anteriorly when it is held out at right angles thereto) I shall speak of as preaxial; those which look ventrally under the first-named condition (posteriorly under the last-named) I shall describe as postaxial. Preaxial and postaxial correspond to the " dorsal " and " ventral " of the Germans. As the basal segment of the axis differs in its essential characters from those which follow upon it, I shall refer to it as the proximal meso-mere (the " zwischen-Stuck " of Davidoff (7), the " erste Glied" of Schneider (23)). II. On the Structure of the Ceratodus Paired Fins in general and of the Pelvic Fins in particular. The majority of observations made thus far upon the fins of Ceratodus bear especially upon the pectoral member ; its pelvic representative has received less attention. Davidoff (7) and Haswell (15) have dealt most fully with it, the last-named author especially as to certain "irregularities" mentioned in the Introduction. Fig. 1 is a faithful representation of the pelvic fin presented by him to Prof. Huxley ; and as it does not appear to correspond with any one figured in his own paper, I proceed to describe it in detail. The fin reached me cleaned and prepared, as represented in the |