1893. SOME NEW BOOKS. 149 



appendages, doubtless sheathed in true horn during Ufe; several of 

 the upper premolars were as complex as the molars, the incisor teeth 

 were reduced in number or wantmg, and the femur had nearly lost 

 its third trochanter. Diplacodon, of the upper or Uinta Eocene, forms, 

 however, as might have been expected from its geological horizon, a 

 perfect connecting link between litanotherium on the one hand and 

 Palaosyops and its allies on the other. In this genus the skull has 

 no horn-like appendages, while only the last of the upper premolars 

 resembles the molars, and the typical three pairs of incisors are 

 retained. 



The evolutionary development of the PahTosyops-Titanothevinm line 

 may, therefore, now be regarded as worked out as fully as that of 

 the Rhinoceroses, and it is curious to notice how closely the two groups 

 follow parallel courses in this respect. Thus, in both there has been 

 a development of horn-like appendages to the skull ; in both the pre- 

 molars have tended to assume a molariform structure, while in both 

 the last upper molar has more or less completely lost the hinder 

 of its two inner columns ; then, again, the more specialised forms 

 in each group have the front of their jaws edentulous. On the other 

 hand, while the most specialised Rhinoceroses have acquired high- 

 crowned (hypsodont) molar teeth, and have reduced the number of 

 digits on the fore-limb from four to three, the Titanotheres have still 

 low crowned retained the (brachyodont) molars and tetradactylous fore- 

 feet of their Eocene ancestors. 



So far as we can gather from his memoir, Mr. Earle seems to 

 consider that the unguiculate Chalicotlierium, in spite of the similarity 

 in the structure of its molar teeth, has no sort of affinity with Palo'o- 

 syops and Titanothevium. This, however, we are not at present pre- 

 pared to admit. R. L- 



The Student's Handbook of Physical Geology. By A. J. Jukes-Browne, B.A., 

 F.G.S. 2nd edition. Pp. 666. London : George Bell & Sons, 1892. Price 7s. 6d. 

 The new edition of Mr. Jukes-Browne's Handbook is too bulky, and 

 would be improved by judicious compression. We would suggest, 

 for instance, that it is quite unnecessary to say so much about the 

 internal state of the earth, considering how little is known, and how 

 likely to mislead is an appearance of knowledge. Already the dogmas 

 of the rigidity of our globe and the stability of the earth's axis have 

 been rudely shaken, and even the mathematicians hesitate. Is it 

 really necessary, also, to ask the unfortunate student to master such 

 terms as metatropy, metataxis, and mctacvasis, and to understand what 

 they mean ? No examiner is likely to expect a knowledge of a 

 number of technical expressions which he does not himself use, and 

 which are not current coin. 



We draw attention to these slight imperfections, for it is evident 

 that the book meets a want, and will have an established place as a 

 class-book for students, if it can be kept within reasonable limits as 

 to size and price. 



Atlas des Algues Marines. By Paul Hariot. Pp. 51. 48 Plates. Paris: 



Klincksieck, 1892. Price 12 francs. 

 This volume of the Librairie des Sciences Naturelles aims at guiding the 

 young phycologist to a knowledge of the more common seaweeds. 

 On the 48 plates there are represented no species (not 108 as stated 

 on the title-page), easily collected on the shores of France, and, with 



