CURRENT LITERATURE. 73 



museums. The author has in many cases examined the type-specimens and in some 

 cases when it was not possible for him to do this, 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 due to the very vague manner in which several specific names, such as 

 biplcx, •plicatills, 2Jol}/pIocus, and 2^ohjgyratus, have been used, owing 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 that its 

 limits must be drawn somewhat artificially. Thus Parkinsonia is distinguished from 

 Perisphindes by the presence of a median ventral furrow, but as this character 

 occurs in some Perisphindes it cannot be regarded as of generic value, and only 

 those forms must be referred to Parldnsonia which combine this character with 

 others, such as the presence of lateral or of ventral tubercles. In other characters 

 Parkinsonia resemljles Perisphindes and supports Teisseyre's view that Parkinsonia 

 is the ancestral form of many of the Perisphindes. This is indirectly confirmed by 

 their geological age, for whilst Parkinsonia commences, according to the author, in 

 the Upper Lias, attains its maximum development in the Inferior Oolite, and dies 

 out in the zone of Oppelia fusca, true Perisphindes commence in this same zone. 

 Again Neumayr's Sirnoceras is distinguished from Perisphindes by the presence of a 

 smooth band on the peripheral area, but the author includes in that genus only such 

 forms as possess that character in combination with others, namely the presence of 

 tubercles and the gradually diminishing number of the bifurcating ribs. To the 

 genus Perisphindes, however, the author refers certain species which have frequently 

 been placed in the genus HiqAites, reserving for that genus only those forms which 

 in addition to the ventral furrow possess marginal or lateral tubercles ; and he 

 transfers to Olcostephanns the groups of stephanoides, desmonolns, polijptychus and 

 virgatus which some authors have placed in Perisphindes. 



There is a short but interesting chapter on the morphology of the shell. Whilst 

 admitting the importance of the character of the remains of former apertures which 

 are preserved on the shell the author does not consider them to possess the taxonomic 

 value that has sometimes been ascribed to them, in fact he considers, and 

 rightly so, that any classification founded upon a single morphological character is 

 arbitrary and unnatural. The author bases his classification upon the principle that 

 the inner whorls of an individual reproduce the morphological characters of the adult 

 of its direct ancestor occurring in the preceding geological stage; but in framing 

 such a classification he has experienced great difficulty owing to the fact that 

 many species of Perisphindes have been hitherto inadequately described, that is to 

 say, all .their important morphological characters, such as the character of the inner 

 whorls and of the body-chamber, the details of the suture-line and the precise form 

 of the aperture, have not been given. 



The author naturally first paid special attention to the geologically oldest forms 

 of Perisphindes, namely those found in the zone of Oppelia fusca, and having care- 

 fully diflerentiated these, sought for their nearest relatives in the next higher geolo- 

 gical stage, and so on through each successive stage of the Jurassic rocks. In this 

 way he has grouped the 367 species of Perispihindes which he has recognized, 

 into a number of " Formenreihe " or groups of contemporaneous species, and 

 these again into a number of " Mutationsreihe " or developmental series; these are 

 arranged in six sections and grouped into five subgenera thus: I. Grossouvria, 

 n. subgen. (including II. Bipliees, Sutner), III. Ataxioceras, Fontannes, IV. 

 Perisphindes, s. str., V. Proccrites, n. subgen., and VI. Chuffatia, n. subgen. 



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, a drawing of the suture line 

 of many of the species, and in some cases also of the form of the aperture, being 

 given in the illustrations included in the text. 



As defined by the author the genus is exclusively Jurassic, the oldest types ap- 

 pearing in the Inferior Oolite, and only a few species reaching to the Neocomian. 

 He considers that the four principal types, viz., Grossouvria, Perisphindes, 



