Geology and Mineralogy. 413 



having perfect apertures, and his plates are the most perfect de- 

 monstration, which we have yet seen, of the importance of the 

 contours of the aperture in the classification of sub-groups. The 

 author divides the genus Arcestes into several divisions according 

 to the peculiarity of the sutures and gives complete tables of the 

 geological and geographical distribution of the species. In fact 

 the stratigraphical paleontology is treated in the most perfect 

 manner. Any criticisms of the zoology of the work would be out 

 of place and inapplicable, since it is essentially, as are all the later 

 German paleontological memoirs on this and kindred subjects, 

 paleoiitological geology; the differences of the animal remains 

 being invariably the aim of all the researches, with the view 

 of establishing data by which the different strata may be distin- 

 guished one from another, and the peculiarities of the faun* noted. 

 Two new genera are described, Didymites and Lobites. The latter 

 being related to the true Arcestes in about the same way that 

 Scaphites is to the typical Ammonites. Whether this will eventu- 

 ally hold or not is doubtful, since, as Quenstedt has shown in his 

 master-work on the Jura, such forms are intimately connected with 

 normal forms, sometimes not even specifically separable according 

 to the generally accepted methods of classification. a. h. 



'7. Mammelsberg : Hamlbuch der Mineral- Chemie. 2d edition, 

 980 pp. 8vo, Leipzig, 1875. — The second edition of Rammels- 

 herg's valuable work on mineral chemistry is an indispensable 

 volume to all interested in the progress of mineralogy. The gen- 

 eral plan adopted by the author is essentially that of the first 

 edition (published in I860), the most important changes being 

 those which strict conformity throughout to the principles of the 

 new chemistry has required. The first volume (136 pp.) contains 

 the general treatment of the subject of mineral chemistry, with a 

 detailed discussion of the principles of isomorphism and hetero- 

 morphism. The second volume (744 pp.) takes up the mineral 

 species in order, giving under each the most of the analyses pub- 

 lished, especially those of recent date. For each analysis the 

 atomic ratios of the different elements have been calculated in full, 

 and from them the formulas are deduced. The author has been so 

 long an authority in mineral chemistry that his present conclusions 

 on many disputed points, though occasionally appearing somewhat 

 arbitrary, will have great weight with all. e. s. d. 



8- Einleitung in die Krystallberechmmg, voK Cael Klein; 

 2^ce^7e Ahtheihoig, pp. 209-393. Stuttgart, 1876.— The first part 

 pf Professor Klein's valuable work on crystallography was noticed 

 }n a recent number of this Journal, (III, xi, 68.) The present part 

 includes a detailed description of the methods of calculation appli- 

 cable to the monoclinic, triclinic, and hexagonal systems, the whole 

 being characterized by the same clearness and thoroughr^ ^- 



