less than it really is. The frontal and premaxillary bones, as already described, are much larger in the American than in the African skull; and as the parts of these bones which form the boundary of the anterior nasal aperture are also broader, thicker, and more expanded from side to side, there is a corresponding difference in form and size of the anterior nasal aperture in the two skulls. The posterior nasal aperture is somewhat less in the American skull. The left bulla tympani is present, but without any opening; it is of an oval shape, keeled beneath, an inch and a half in length, an inch broad, and rather more than half an inch in thickness. It is attached in front by a short twisted process to the anterior portion of the pars petrosa, and by another larger transverse process behind. There is a deep oval depression at the upper and back part, a third of which is open above and a little in front, the roof being formed by the under concave surface of the anterior process of the petrous bone, which is lodged in a deep cavity at the under and back part of the root of the zygomatic arch. The pars petrosa and the posterior process occupy another depression, formed partly by the root of the zygomatic process and partly by the mastoid bone. The posterior process of the pars petrosa slightly projects externally by a transverse opening more than an inch in length, and half an inch from above downwards, situated between the occipital and mastoid bones, corresponding to the position of the foramen mastoideum. The anterior and posterior processes of the petrous bone, which are quite distinct in the Baleen cetacea, are so compressed together with the petrous part in this skull, as to appear to form but a single bone, about 2 inches in length, and rather less in breadth. The lower jaw is less massive than that of the African skull. Its length on each side, from the incisive edge to the angle of the jaw, is 73 inches, and the depth about 2 inches. The perpendicular height from the angle to the condyle is 5th inches, and the posterior part of the rami curves upwards from the angle towards the root of the condyle, but is nearly straight in the African skull, The distance from the condyle to the anterior point of the co ronoid process is nearly 4 inches, the upper border of the coronoid process rising two-thirds of an inch higher than the condyle. The maxillary canal greatly exceeds in size that in the African skull, and is not separated from the inflated extremity of the alveolar process posteriorly. It terminates in front in a wide-grooved foramen menti, with another foramen behind, which communicates with the maxillary canal, and is equal in size to the true foramen menti in the African skull. The distance from the angle of the lower jaw to the symphysis menti is about 4 inches, and the angle of the jaw is but slightly inflected, whilst in the African skull there is an acute inflected angle, the two inner points of the angles being only 3th inches apart. In the lower jaw of the skull from Honduras, the distance between the two inner points of the angles is 4th inches. The alveolar process of the lower jaw is 5 inches in length, slightly curved outwards and upwards at the posterior termination, where it perforates the roof of the coronoid process, and protrudes by its inflated extremity into the maxillary foramen. There are eight molar teeth on the left side of the lower jaw, and an empty socket in front; each tooth has two large transverse bi-tuberculated ridges, and a smaller ridge behind, implanted by two roots in sockets about an inch deep, like those in the lower jaw of the African skull. The roots of the teeth are flattened transversely, corresponding to the transverse coronal ridges, and the posterior root is bifurcate at the apex. The molar teeth in the upper jaw have two transverse trituberculated ridges, with a ridge-like thickening at the cervix anteriorly and posteriorly, similar to, but less in size than those in the African skull. Each molar tooth in the upper jaw has three roots, the inner root compressed longitudinally, the two outer roots compressed transversely; but the roots of the teeth are less divergent, and the external anterior root is less curved backwards, than those in the African skull. The three posterior teeth on each side of each jaw are nidamental; the three succeeding teeth are but very slightly worn; whilst those in front, still in situ, have their crowns much worn down and hollowed out in the middle, showing the central brown dentine, surrounded with a coat of enamel, and a slight outer layer of dark coloured cementum. m 9-9 = 36. 9-9 There are fifteen molar teeth remaining in the upper jaw, and fifteen in the lower, with six distinct empty sockets; the dental formula in the skull from Honduras is, therefore, It appears to have been from the American species, the Manátus australis of the British Museum Catalogue, that Daubenton, Cuvier, Gray, and others, have adopted the dental formula of the genus Manátus. In the British Museum Catalogue for 1850, the number of grinders in the genus Manátus is said to vary according to the age or state of the specimens, but when complete to be m 9-9 9-9 = 36. It is added that the front ones are often deciduous; hence Sir Everard Home describes them as m 6-6 = 24, and Cuvier as m 8-8 There is no skull of the African species mentioned in the Catalogue as existing in the British Museum; and there is none described in the Catalogue of the Royal College of Surgeons of London; and at a meeting of the British Association held at Cheltenham in 1856, Professor Owen stated, that he had not then had an opportunity of examining the dentition of the known African Manatee. The difference in the number of the molar teeth in these two distinct species corresponds with the difference in the length of the aveolar portion of the palate, and with other corresponding modifications which have been shown to exist between the two skulls. I am indebted to Professor H. D. Rogers of Glasgow for an opportunity of comparing the skull of the Manátus australis, with that of the Manátus senegalensis; and the result of this anatomical comparison appears to me to justify the 11-11 conclusion, that m = 44, is the normal number of 11-11 the dental formula for the genus Manátus, as this number was found to be present in the skull of the Manátus senegalensis, which inhabits the rivers at Old Calabar. III. Historical Review of the State of our Knowledge respecting Metamorphism in the Mineral Kingdom, with special regard to certain recent Researches. By JOHN S. LIVINGSTON, Esq. Mr Livingston stated, that within late years great additions had been made by the labours of chemical geologists to our knowledge of the more recondite geological phenomena. To these additions he wished to direct the attention of the Society, as they seemed in this country to have, in a great measure, escaped notice. After expressing his opinion that, if we are to make any advances in our knowledge of the deep-seated causes of metamorphic changes, it must be brought about by introducing into the methods of geological research much more of the experimental than had hitherto been considered necessary, he rapidly sketched the progress of inquiry into metamorphism. Every year was enabling us more and more to imitate the mineral productions that occur in nature, though we cannot reproduce all the conditions. under which they were formed. What the influence of the long lapse of ages might have been, must of course ever remain an insoluble problem. After passing under review the opinions of Hutton, Mr Livingston referred to the experiments of Sir James Hall, but especially to his having succeeded in producing a crystalline marble, by placing powdered calc spar in a gun-barrel hermetically sealed, and exposing it to a high temperature,-an experiment that had been recently impugned by Gunstav Rose, but on insufficient grounds. Reference was then made to the processes adopted by Berthier, H. Daville, and Caron, for artificially producing minerals by fusion alone, and especially to the production of corundum by Ebelman. But the most important results were obtained when Senarmont, by experimenting on minerals with water at high temperatures, and under enormous pressures, produced crystalline quartz, spathic iron, sulphate of baryta, and sulphide of antimony. Daubrée in 1857 had, by using a temperature of 572° Fahr., converted wood into anthracite; and Baroulier in 1858 obtained coal VOL. II. 2 M by placing vegetable matter in moist clay, and exposing to heat. Daubrée's observations made at the thermal springs of Plombières were next mentioned. These issue, with a temperature of about 172° Fahr., from a porphyritic granite in the mountains of the Voges. To convey the water of the springs to the baths, which the Romans had built there, a structure of brick and sand had been erected. Through this the water had trickled. On breaking into the mass numerous minerals of the zoolite family were found, but chiefly Apophyllite and Chabasite. Mr Livingston then mentioned the extensive changes effected by the juxtaposition of certain rocks, and especially the phenomenon termed Endomorphism by Fournet. He then discussed the bearing of these and other facts, and showed that, though the hypothesis of a central fire would undoubtedly explain much, yet that it would not all. If heat were the only agent in these changes, he asked why did they not take place according to the known laws of the propagation of heat and the conductibility of rocks? That water had to do in effecting these changes was evident from the occurrence of chiastolite, augite, garnet, and felspar in sedimentary rocks. The presence of water chemically combined in the masses ejected by volcanoes was a proof that it played an important part in the phenomena that take place at great depths. He then referred to the facility with which minerals, and especially the silicates, can be formed when water is present, to Daubrée's production of Wollastonite, to his process of forming the anhydrous silicates in the moist way, and his production of a substance like mica and chlorite. Mr Livingston believed that these researches invite us to hesitate before we commit ourselves to the views of the igneous rocks at present in vogue, and expressed his conviction that the faith of geologists, after much weary tossing between fire and water, would finally settle down somewhere between these two extremes. A conversation followed on the plutonic and aqueous agencies in the formation of rocks, and on the probable aqueous origin of granite, in which Professor M'Donald, Mr Alex. Bryson, and others, took part. |