326 Heports and Proceedings — Geological Society of London. 



amount of labour and research. For the present monograph of this 

 ■very extensive genus the author therefore deserves our best thanks. 

 He tells us that in its preparation he has consulted 128 separate 

 publications in German, French, English, Italian, Spanish, Polish, 

 and Russian ; and that besides his own collection, which contains 

 several hundred examples of the genus, he has examined the col- 

 lections of several private individuals, as well as those of various 

 Continental museums. In some cases in which the author was 

 unable to see the type-specimens he obtained plaster casts of them, 

 in order to gain a correct idea of the species. One great difficulty in 

 dealing with this genus is caused by the very vague manner in 

 which several specific names, such as biplex, plica tiJis, pohjplocus, and 

 poJygyrntus, have been used, due in some cases to the inadequate 

 description or figure of the type-specimen. The author concludes that 

 a precise limitation of the genus from allied genera is not possible, and 

 thatitslimits must be drawn somewhat aitificially. Theauthordevotes 

 a short but interesting chapter to the morphology of the shell, and 

 then proceeds to the classification of the genus, in which he recognizes 

 about 367 species, only a few of which are new. His investigations 

 lead him to divide the genus into six sections, which he groups into 

 five subgenera, thus: — I, Grossouvria, n. subgen. (including II, 

 BipUces, Sutner) ; III, Ataxioceras, Fontannes ; IV, Perisphinctes, 

 s. str. ; V, Procerites, n. subgen. ; and VI, Choffatia, n. subgen. 

 These are divided into ' Mutationsreihe,' or developmental series, and 

 these again into ' Formenreihe,' or groups of contemporaneous species. 

 The author gives a description of each species, lateral views of the 

 new forms and of some others are given on the eight photographic 

 plates accompanying the work, an outline of the transverse section 

 of the whorl and a drawing of the suture-line of many of the species 

 being given in the illustrations which are included in the text. 

 There is an index to the work, but this appears to be somewhat 

 incomplete. G. C. C. 



I2.EI=OiaTS .iLlsTX) :PS,OGE!E3IDI3SrC3-S. 



Geological Society of London. 



I.— May 10, 1899.— W. Whitaker, B.A., F.E.S., President in the 

 Chair. The following communications w^ere read : — 



1. " The Geology of the Davos District." By A. Vaughan 

 Jennings, Esq., F.L.S., F.G.S. 



Alpine geology has attracted many workers since the date of 

 Professor Theobald's classic memoir on the district of which Davos 

 forms part, and new principles of interpretation have been 

 established. The author has more especially studied (a) the age of 

 certain rocks formerly classed as ' Biindner Schiefer,' but distinct 

 from the grey shales variously regarded as of Jurassic or Tertiary 

 age ; (h) the origin and date of the serpentine near the Davoser 

 See ; and (c) the tectonic structure of the district. The following 



