598 



NA TURE 



{April so, 1885 



relate, it owes its recognition as such to two rami of the 

 mandible ! 



re at firs: puzzled by the numbers applied to 

 certain premolars in the author's description of the denti- 

 tion of some fossil species belonging to still existing 

 genera, until the following paragraph in the Introduction 

 was noticed : — " In enumerating the teeth of the typical 

 heterodont Eutherian mammals, each tooth of the cheek 

 series is referred to its proper position in the complete 

 series, the first premolar always meaning the first tooth 

 in the typical series of four, and so with the succeeding 

 teeth." Mr. Lydekker has therefore resuscitated what 

 we had thought was long defunct — namely, the Owenian 

 system of expressing the homology of the teeth by ima- 

 gining a fixed mode of reduction for a typical number of 

 44, of which the premolars, for instance, when reduced in 

 number, are supposed to become so by symmetrical loss 

 from before backwards ; so that when, for example, two 

 upper premolars alone remain, these must be considered 

 to be the third and fourth. It is, however, an incontro- 

 vertible fact that in many species of mammals it is the 

 third premolar in the upper jaw that is wanting, that 

 further reduction is accomplished by the loss of the 

 second, and, lastly, of the first premolar, the fourth pre- 

 molar of the original series alone remaining, this tooth 

 very rarely disappearing also. In the lower jaw of certain 

 species with three premolars the second premolar is the 

 first to disappear, so that here the same difficulty exists- 

 Were the mandible of such a species to become fossil, the 

 two remaining premolars would, by the Owenian system, 

 be recognised as the third and fourth, whereas they would 

 really be either the second and fourth or the first and 

 fourth. Indeed Prof. Owen himself notices (" Anat. 

 Vertebr.." iii. p. 374) that "in some instances the first 

 premolar remains of small size when p. 2 and p. 3 are 

 lost ; " and Prof. Flower, commenting on the theory of 

 reduction advanced by Prof. Owen, remarks (" Encycl. 

 Brit., 1 ' xv p. 353) that " if this were invariably si 

 labours of those who describe teeth would be greatly 

 simplified ; but there arc unfortunately so many excep- 

 tions that a close scrutiny into the situation, relations, 

 and development of a tooth may be required before its 

 nature can be determined, and in some cases the 

 evidence at our disposal is scarcely sufficient for the 

 purpose." 



Space will not admit of entering upon a criticism of the 

 geological horizons adopted, which, so far as the Tertiaries 

 of Europe are concerned, have been slightly modified by 

 the author from the tables given by Gaudry, Boyd 

 Hawkins, and Max Schlosser. We note, however, with 

 satisfaction that he has rejected the prevalent notions as 

 to the position of the Siwalik and Pikermi beds, referring 

 the ossiferous strata of the former to the Upper and that 

 of the hitler tt. tin Lower Pliocene— a view, if we mistake 

 not, urged for some time past by Mr. W. T. Blanford. 

 We could wish for a special note on the position of the 

 Caylux and Quercy phosphorites of Central France, 

 referred to the Upper Eocene ; for the highly specialised 

 character of the mammalian remains from these deposits 

 appear to throw much doubt on their supposed age. 



Where there is much to blame there is also much to 

 praise : the descriptions appear to be in most cases ex- 

 cellent and carefully worked out, the subjects chosen for 



illustration well selected, and the woodcuts (thirty-three) 

 well executed. We hope that this volume and the next 

 (which will probably include the remaining species of 

 fossil Mammalia represented in the collection) will to- 

 gether form but a " Prodromus '' to ,1 catalogue of fossil 

 Mammalia by the same author, which, while equalling 

 in comprehensiveness the best of the hitherto published 

 catalogues issued by the Trustees of the British Museum, 

 shall, however, surpass all of them in accuracy of de 

 scription and in the number and excellence of its 

 illustrations. 



THE SELF-INSTRUCTOR IN NAVIGATION 

 The S el fi- Instructor in Navigation and Nautical Astro- 

 nomy for flu- Local Marine Board Examinations and 

 for Use at Sea. With numerous Examples, Illustra- 

 tions, Diagrams, and Charts. By W. H. Rosser. New 

 and Thoroughly Revised Edition. (London : Imray 

 and Sons, 1SS5.) 



BOOKS of this character have presumably their use ; 

 and this particular one is neither worse nor better 

 than many others which owe their being to the necessities 

 of the examination room rather than to the wants of the 

 practical navigator. Its table of contents is framed 

 according to the schedule of the Board of Trade ; and 

 though it is spoken of in the preface as " adapted for use 

 at sea,' 7 Mr. Rosser has proved in other books that he 

 knows it can be so considered only as an indirect com- 

 pliment to the Board of Trade Examinations, which have 

 been carefully devised so as to call for the greatest possible 

 amount of cram and the smallest possible amount of real 

 knowledge. The "Self-Instructor" has run through 

 many editions, and no doubt answers the purpoi 

 author sufficiently well : it is, he says, essentially practical 

 and not theoretical ; though he omits to say that practical 

 is to be understood as referring to what is wanted for the 

 examination, and that theoretical refers to an;- n 

 or intelligent mode of working. It is not Mr. Rosser's 

 fault that the examination is laid down on such clumsy 

 and really unpractical lines ; and what he has professed 

 to do he has done fairly well : though it would be as well 

 to expunge from future editions the symbol given on p. 2, 

 for the " observed distance between the sun's near limb 

 and the moon's far limb" ; more especially if the symbol 

 is to be used, as on p. 304. for a distance observed to the 

 moon's near limb. 



As a little matter of history, it may be remarked that 

 the statement on p. 364, that the method oi determining 

 the latitude by the altitudes of two stars on the same 

 hour-circle was originally given by Mr. Boll in the 

 Nautical Magaeine fc* 1874, is not quite accurate. Mr. 

 Bolt, in the article referred to, makes no claim ol 

 i i merely says that the problem may be new to 



many even expert calculators. In point of 1 

 method suggested itself to, and was taught and practised 

 by, the writer of this notice in 1859. and was introclui ol 

 by him into the examination papers of th< i •> 

 College in 1 866 ; since which time it has been repeatedly 

 set as a theoretical question. In reality, it ought only to 

 be so considered ; for though it gives very good results, 

 and the observation is by no means a delicate one,.a 

 rough approximation to the interval of tune being quite 



