REVIEWS 171 



place of the discovery of edges which indicate axes of reference, is properly pointed 

 out on p. 66. It is questionable if the treatment of forms of lower symmetry within 

 a system as " merohedral " types is wise from the point of view of natural history. 

 Sir William Beale clearly recognises (p. 65) that the constituents of such crystals 

 are incapable of producing more symmetrical forms. While "hemimorphism" 

 remains a useful term to express dissimilar termination at opposite ends of a 

 crystallographic axis, the conception of "hemihedrism " and "tetartohedrism " 

 (p. 113) may well be abandoned, when we consider external form as dominated by 

 the internal space-lattice. Hemihedrism thus seems to belong to geometry rather 

 than to natural history ; and, as the author points out (p. 115), pioneers like Rome 

 de l'lsle and Haiiy dwelt on the importance of the type of homogeneous arrange- 

 ment throughout a crystal as controlling the faces that could be produced. 



Two appendices are added, one on methods of calculation and one on the 

 drawing of crystals. The author's illustrations are clear, and the forms are 

 accompanied throughout by their stereographic projections. Something seems 

 to have gone wrong in fig. 65c* ; but it may be presumed that the student will be 

 encouraged to use models as well as drawings, and to read the symmetry from the 

 disposition and number of the planes. The book, as might be expected, is hand- 

 somely produced, and we notice very few misprints. The round O on p. 10 to 

 express an infinitely small index should be 0, and, conversely, Naumann's symbol 

 on p. 32 should be OP instead of OP, while O and not should stand for the 

 octahedron. The author employs "pinakoid ' : for a single plane only (pp. 21 and 

 32), and individual planes should not, we think (pp. 32 and 33), be described as 

 "prisms," "domes," and "pyramids." The naturalist would like to see more 

 emphasis, with the printer's aid or otherwise, laid on the law of rational indices on 

 p. 10. The student, however, who has progressed for some distance on more 

 conventional lines will welcome this book as lifting him out of many difficulties. 



G. A. J. Cole. 



PALAEONTOLOGY 



American Permian Vertebrates. By Samuel W. Williston, Professor of 

 Palaeontology in the University of Chicago. [Pp. v + 145, with 32 text- 

 figures, frontispiece, and 3S plates.] (London : Cambridge University Press. 

 Price 10s. net) 



In such a rapidly advancing science as vertebrate palaeontology it is not a little 

 difficult to review a book which has already been in circulation for four years, 

 especially when, as in the present instance, the author has subsequently issued 

 what is in many respects a companion volume {Water-Reptiles, Chicago, 1914), 

 which to some extent covers part of the same ground, and contains modifications 

 or expansions of views tentatively enumerated in the original work. The reason 

 for such delay is that the edition for the United Kingdom has only just been 

 issued by the Cambridge University Press, to which the editor is indebted for 

 a copy. 



As stated in a paragraph in my article on vertebrate palaeontology for 191 1, 

 published in the April number of Science Progress for 191 2, Prof. Williston's 

 volume contains what were at the time of its original publication several emenda- 

 tions in regard to the classification of primitive amphibians and reptiles, notably 

 the separation of all the groups of the latter with complete skull-roofs, such as 

 the North American Pariotichus and the South African Pariasaurus and Cistc- 

 ccphalus from the typical mammal-like reptiles and their inclusion in the 



