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vine basalts corresponding to geological masses intermediate in characteristics between volcanic sheets and necks. In many of the neck rocks the hornblende is seen to have been partially resorbed and changed to augite. The continuation of the resorbtive process until every trace of the hornblende was dissolved, may account for the absence of the mineral in the sheet rocks.

Petrographical Notes.-In an article whose aim is to call forth more accurate determinations of the feldspars in volcanic rocks, and one which gives a practical method for making this determination, Fouqué has described briefly the volcanic rocks of the Upper Auvergne, the acid volcanics of the Isle of Milo and the most important rocks in the Peleponeses and in Santorin. Among the varieties described are doleritic basalts, andesitic basalts, labradorites, andesites, obsidians, trachyte andesites, phonolites, andesitic diabases, rhyolites, dacites and normal basalts. The labradorites are composed largely of microlites of labradorite with a few augites and tiny crystals of olivine in an altered glassy base. In all these cases the author has shown that the rocks contain several different feldspars at the same time, and in each « case he has determined their nature. The method made use of in the determination is based on the observation of extinction angles in plates cut perpendicular to the bisectrices.

In a well written article on complementary rocks and radial dykes Pirsson" suggests the name of oxyphyre for the acid complementary rock, corresponding to the term lamprophy re for the basic forms. He also calls attention to the fact that the dykes radiating from eruptive centers are usually filled with younger material than that which composes the core at the center. The dykes cutting the central mass will generally be oxyphyres and the more distant ones lamprophyres.

Cordierite gneisses are reported by Katzer1 from Deutshbrod and Humpolitz in Bohemia, where they are intruded by granite veins, and where masses of them are occasionally completely surrounded by granitic material.

In the examination of a large series of granites and gneisses from the borders of the White Sea, Federow" discovered that garnet is present in large quantities when plagioclase is absent and vice versa.

In a general article on the Catoctin belt in Maryland and Virginia,

Bull. Soc. Franc. d. Min., XVII, p. 429.

Amer. Journ. Sci., 1895, p. 116.

10 Min. u. Petrog. Mitth., XIV, p. 483. 11 Ibid, p 550.

Keith" gives very brief descriptions of the granites, quartz porphyries, andesites and the Catoctin schist of the region. The last named rock is apparently a sheared basic volcanic. All the rocks present evidence of having suffered pressure metamorphism.

GEOLOGY AND PALEONTOLOGY.

Notes on the Fossil Mammalia of Europe.-I, COMPARISON OF THE AMERICAN AND EUROPEAN FORMS OF HYRACOTHERIUM.Historically speaking Hyracotherium is one of the oldest of known fossil Perissodactyla, and it is of importance phylogenetically to compare the representatives of this genus in Europe with those of America, in order to acquire an exact knowledge as to the evolution of the molar cusps of the New and Old World species. My attention was called to this subject on account of having studied Euprotogonia of the Puerco, a genus which as well known, is considered to have one of the most primitive types of Ungulate molars.

The importance of having accurate drawings of the teeth of fossil mammals is nowhere better illustrated than in Hyracotherium. In the case of the enlarged drawing of the teeth' of H. (=Pliolophus) vulpiceps which has been copied extensively in works on vertebrate palæontology, we obtain quite an erroneous idea of the exact form of the molar cusps.

Kowalevsky' in his great work on "Anthracotherium" figures some of the molars of the type of Hyracotherium namely: H. leporinum, and I should judge from his description that he had studied Owen's type in London. However, his criticism of Owen's drawing of the type of Hyracotherium is very accurate, and as Kowalevsky remarks, Owen's figures gives one the idea that the teeth of the type are strictly bunodont, whereas they are really transitional in structure between a real bunodont type, such as Euprotogonia and a truly lophodont form like Systemodon.

1 14th Ann. Rep. U. S. Geol. Survey, p. 285.

'Jour. of the Geog. Soc. of London, 1858, p. 54.

2 Monographie der Gattung Anthracotherium, p. 205.

On my recent visit to London3 I took the opportunity to examine both of the types of Hyracotherium (H. leporinum and H. (=Pliolophus) vulpiceps). In general the external cusps of the superior molars in both forms is lenticular in section, being considerably drawn out anteroposteriorly, and the intermediate tubercles are well extended transversely. In the drawing of the type specimen of H (=P.) vulpiceps the molars are represented as greatly enlarged, and their internal portions shown as complete. In the original specimen the teeth are damaged internally, and it is with some diffiulty that the form of the cusps can be made out. However, I am satisfied that the internal cusps are not really bunodont as shown in the plate, but like the American forms of Hyracotherium these cusps are extended transversely and form by wear slight ridges with the intermediate tubercles. In comparing the upper molars of both types of Hyracotherium of England with those of the Wasatch of America, I find them to be in exactly the same stage of evolution as to the form of the cusps.

Lydekker speaks of the posterior transverse crest of the upper molars in the type of H. (=P.) vulpiceps as not being represented as sufficently well developed in the plate, but this crest on the last molar is drawn. correctly, and on the other two molars it is as nearly as well developed. A comparison of the upper molars in both types of Hyracotherium with those of Euprotogonia, reveals the fact that the form of the cusps in the former genus has undergone a progressive change; and this is seen especially on the last upper molar which is quadritubercular with a large development of the metaloph, whereas in Euprotogonia the last upper molar is tritubercular. Again the third upper premolar in the English types of Hyracotherium is tritubercular whereas in Euprotogonia, this tooth has only one external cusp.

The species of H. (Pliolophus) vulpiceps is of importance, as in this specimen we have both upper and lower teeth belonging to the same individual. I should like to particularly emphasize the point that the last lower premolar in the type of Pliolophus is simpler in structure than the first true molar, the posterointernal cusp being absent. This character distinguishes this type from some forms of the American Wasatch which have been referred to Pachynolophus.

I wish to express here my thanks for the privileges I enjoyed in examining specimens in the British Natural History Museum, and especially to thank Sir W. H. Flower for his kindness. I am also indebted to him for having been able to visit the Royal College of Surgeons. Mr. C. W. Andrews of the Geological Department. I am also much indebted for his many courtesies.

Catalogue of Fossil Mammals in British Museum. p.11.

The question now arises what is Pachynolophus, or in other words what is the exact generic definition of this genus, and does it really occur in the Wasatch of America. It is usually stated that Pachynolophus is separated from Hyracotherium by the fact, that the last premolar is molariform but as far as I have been able to investigate, this definition will apply to only one European species, namely: Pachynolo phus (Hyracotherium) siderolithicus, and even in this species the last upper premolar exhibits a good deal of variation in its structure. Rütimeyer figures Pictet's species, P. siderolithicus, which in this specimen has the last upper premolar molariform, but in the same plate (fig. 21) is given another last upper premolar, which Rütimeyer referred to the same species. This tooth is tritubercular, or simpler in structure than the true molars.

Among the specimens of Pachynolophus in the collection of the Jardin des Plantes, Paris, there is a series of loose teeth from the Siderolithic du Mauremont, which are of considerable interest as they were studied by Kowalevsky, and referred by him to P. siderolithicus. This series contains at least one last upper premolar, and it has exactly the same character as that figured by Rütimeyer, in other words this is another case in which this tooth in P. siderolithicus is simple in structure. In Pachynolophus duvalii as figured by Rütimeyer, the last upper premolar is tritubercular, and this tooth has the same structure in P. desmarestii. In Pachynolophus cessarasicus figured by Filhol from the Middle Eocene of Céssai, the last upper premolar has only one internal cone and the two transverse ridges diverging from it are well developed. The length of the skull in this species is about one-third greater than that of Hyracotherium venticolum of the Wasatch.

Numerous species of Pachyrolophus occur in the different horizons of the Eocene of France, but in nearly all cases, they are represented either by upper or lower molars which were not found together. I believe the English Hyracotherium leporinum is the only known form in Europe in which both upper and lower molars were found associated, and actually belong to the same individual.

As is well known it is the last lower premolar which first becomes molariform, consequently if we find forms in which this tooth is simpler in structure than the molars, we can safely conclude that none of the superior premolars are molariform. In a jaw referred to Pachynolophus in the collection of the Jardin des Plantes from Phosphorites, containing all the lower premolars, the last tooth of this series is not molari$ Eocäne Sangethiere Welt von Egerkingen, pl. III, figs. 18–21. Vertébres Fossiles d'Issel Mém. Soc. Geog. de France, 1888, pl. XX, fig. 13.

form. As the Phosphorites are considered to represent the top of the Eocene, we should certainly expect to find in any species of Pachynolophus from this formation the last premolar as complex in structure as the molars. In this jaw, however, the last premolar is not molariform and the collection contains a crushed skull of the same species of Pachynolophus in which all the superior premolars are simpler in structure than the true molars.

I can find no good generic differences based on tooth structure separating Propalæotherium from Pachynolophus, and shall consider the former genus as a synonym of the latter in this paper. In Propalaotherium the species are much larger than in those of Pachynolophus, but certainly size alone can not be considered as of value in generic definitions. In all of the species included in Propalæotherium, the premolars are simpler in structure than the true molars.

I believe, however, if we divide the various known species of the Hyracotheriina into genera according to the complication of the premolars, that we shall be adopting an artificial character, and as shown above. Of all the known forms of Pachynolophus, P. siderolithicus is the only one in which the last upper premolars is molariform and even this species shows considerable variation in this respect. I conclude then that the only natural classification of these forms is a careful analysis of the form of the molar cusps, and to group the species into genera according to the development of the same; I refer here especially to the European forms of Hyracotherium and Pachynolophus.

Having thus attempted to show that in nearly all the European species of Pachynolophus the last premolar is simpler in structure than any of the true molars, I come to consider what are the generic differences separating Hyracotherium from Pachynolophus. Kowalevsky studied Pachynolophus siderolithicus, and if we compare the molars of this species with those of Hyracotherium angustidens from the Wasatch of America, we observe at once that the external cusp of the upper molars in the latter species are nearly round in section, and they are scarcely at all flattened. There is no mesostyle and the height of the crown is very low or strongly brachydont. In P. siderolithicus the ectoloph is considerably lengthened from above downwards, and the external cusps are strongly flattened, with a prominent mesostyle. In all the species of Pachynolophus which I have studied the molar crowns are higher than those of Hyracotherium, and in all the mesostyle is strongly developed. The latter characters demonstrate that the molars of Pachynolophus have reached a higher stage of evolution than those of Hyracotherium, and this transformation in the form of the molar cusps

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