AT. from the Fig. 1.--Femur

Downloaded from http://jgslegacy.lyellcollection.org/ at University of California-San Diego on December 19, 2016 456 H. G. SEEL~ ON A MAMMALIAN FEMUR AND 35. No~E on a Fsmra and a H~vs of a sx,~ MA,~AT. from the S~O~SF~LV S~r~. By H.G. S~.~Y, Esq., F.R.S., F.G.S. (Read February 26, 1879.) WHrLE examining, with the assistance of Mr. W. Davies, F.G.S., the unarranged and more fragmentary remains of Pterodaetyles from the Stonesfield Slate which are preserved in the British Museum, I was so fortunate as to detect two small slabs which contain, in good preservation, a small mammalian femur and a mammalian humerus of corresponding size. Mr. Davies has had as much of the matrix removed from these bones as was necessary to fully display their essential characters ; and I now offer to the Geolo~cal Society a brief account of the remains, for the opportunity of making which I would express my thanks to Mr. Waterhouse. It is perhaps impossible to determine with absolute certainty whether they belong to AmThi- therium, Phascolotherium, or to some new type, or whether the bones might not perhaps have belonged to two different animals ; but, on the chance of their being naturally associated, the generalized marsupial characters which they manifest make a useful contribution to our knowledge of that animal type, which has hitherto only been known, from Stonesfield, by rami of lower jaws. The right femur rests flat in the matrix, so as to expose the aspect Fig. 1.--Femur. of the bone, which during life was posterior and inferior. The ex- treme length of the specimen is 17~v inch. It has a straight aspect, is moderately expanded proximally, less enlarged at the distal end, and has the spheroidal articular head in- dined to the inner side and looking slightly forward. The most remarkable feature of the specimen is the expansion below the articular head of the two ~rochanteroid pro- cesses, which make the width of the bone in this position something less than ~ inch. The'inner trochanter is much the less massive of the two ; but its margin is imperfectly preserved, and it was obviously thinner than the great trochanter. It extends proximally to near the base of The outline shows the natural size the proximal articular head of the of the bone. bone, and had a narrow wing-like extension inward, curving somewhat forward at its proximal margin ; but, as preserved, its internal Downloaded from http://jgslegacy.lyellcollection.org/ at University of California-San Diego on December 19, 2016 HUMERUS I~RO~ THE STONESFI~ELD SLATE. 457 extension beyond the proximal articulation is hardly more than inch. It is in no sense a process, but simply an expansion of the bone, and terminates distally in a short sharp ridge on the angle of the side of the shaft. The external trochanter is much thicker, and extends beyond the border of the articular head for T2~yinch. It is separated from this convex surface by a concave excavation about -~o inch wide ; and its outer rounded border, which is nearly T~ inch thick, is reflected backward, and terminated proximally in a rounded process, which at the proximal end curves a little forward. The rounded articular head has no neck connecting it with the shaft; but a constriction extends below the globular surface pos- teriorly, and another depression is apparently more marked on the anterior aspect. The transverse measurement of the head is about ~_a inch, and the antero-posterior measurement is somewhat more. Its depth on the posterior aspect is about ~ inch. Between the head of the bone and the two trochanters is a concave space, which runs down the shaft for about one third of its length, disappearing in a line as the bone narrows from side to side, and it is deepest towards the great trochanter. There is no trace of an obturator pit, nor of any excavation towards the external trochanter, such as characterizes this part of the bone in the majority of mammals, and especially marsupials; so that at first sight there is a primd facie suggestion in this region of bats, or moles, or of a type allied to the monotremes, in which the trochanters were less developed than in Ornithorhynchus; but there are slight concavely curved lines extending between the trochanters and indicating muscular attachment. The shaft becomes reduced to its least width of about .-f-r inch near the middle. Its posterior lateral outline is concave, so as to give the distal articulation the aspect of being produced slightly outward. The internal outline is nearly straight between the internal troehanter and the distal articulation. The shaft of the bone is evidently flattened naturally, is straight on the posterior aspect below the trochanters, and becomes convexly curved from side to side. There is a slight groove extending down the length of the shaft in the median line from the external trochanteroid ridge to between the condyles, and gradually widening distally. The width of the bone across the distal condyles is rather less than a inch ; and though the specimen is not sufficiently developed from the matrix to show the thickness of the condylar end, it was evidently much less thick than is usual among marsupial mammals. The outer condyle is the larger; it has a transversely ovate outline, and is divided on the posterior aspect by a moderately deep depression from the smaller inner condyle, in which the greatest measurement was vertical. The depth of these condyles is about T~ inch, and the shaft above them is concavely excavated. These are the characters on which the systematic position of th6 animal must be determined. The bone is altogether less robust and is rather smaller than the same bone in Ornithorhynchus, has the trochanters narrower and smaller, the distal condyles narrower, Downloaded from http://jgslegacy.lyellcollection.org/ at University of California-San Diego on December 19, 2016 458 H. G. SEELEY ON A MAMMALIAN F]~MUR AND and the articular head directed less upward and more inward. In all these points of difference there is a nearer approach to the femur of Echidna, which, however, is twice as long. In that genus the trochanters are relatively less developed, and the head of the bone is less well defined on the inferior aspect, while in the fossil the internal trochanter has a greater proximal extension. Both these genera of living Monotremes agree in possessing a similarly unex- cavated condition of the posterior aspect of the external trochanter ; and there are enough intermediate steps between the two surviving genera to include such a form as this fossil bone, if there were any corroborative evidence to justify its location in the same order with them. Among the marsupials there are not many in which a sufficiently near correspondence can be detected to justify a comparison. It is only among some of the Phalangers, such as Phalm~gista Cookii, that there is a general resemblance seen in form and type, though the existence in that group of an obturator pit renders detailed comparison impossible. The only other marsupial to which reference may naturally be made is the Myrmecobius, interesting from its resemblance to Ampl~itherium ; but the bone is relatively shorter than in Myrmecobiusfasciatus; the condyles at the distal end are relatively much less thickened. The internal troehanter does not ex- tend so far proximally in the recent genus, and the fossil shows no trace of the excavation of the inferior aspect of the proximal end. It may therefore be concluded that the resemblance to Marsupials is, on the whole, less evident than the probable affinity of the bone to a Monotreme. It is interesting that Amphitherium has presented characters in the inflected angle of the lower jaw which induces Prof. Owen to dwell on its resemblance to the mole and the hedgehog, and to express a necessary caution against hastily concluding that the animal was not insectivorous. Dr. Gill, one of the most profound systematists of modern times, has sufficiently recognized, in his tabular view of the classification of the Mammalia, the near affinity of the Chiroptera, Insectivora, Rodents, and Edentates with the Marsupial and Bionotreme orders; and it is certainly remarkable that this fossil bone, like the jaw referred to, should present characters which necessitate close examination as to its placental or its implacental determination. There are many animals in which the proximal end of the femur has two well-developed trochanters, and frQm which the obturator pit is absent ; but in none do the condyles attain so great a size as in the fossil. In the Little Ant-ester (Oycloth~,r,s didact!flus) the femur is 11-~ inch long, while the transverse measurement across the trochanters is only ~ inch, so that in this animal the shaft is 3] times as long as the transverse measurement over the trochanters, while in the fossil the shaft is not more than twice as long as the width over the trochanters. The femur of the Mole has only a general resemblance to the fossil ; the trochanters are narrower ; the great trochanter is more developed proximally, and the concave area between the trochanters is of an altogether different character. A similar remark Downloaded from http://jgslegacy.lyellcollection.org/ at University of California-San Diego on December 19, 2016 HUMERUS l~RO~f THE STON]~SFIELD SLATE. 459 applies to the proximal end of the femur of the Hedgehog, which at first sight approximates in form to the fossil.

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