Bibliographical Notices. 363 



To show the use of the Chart to the student, we cannot do better 

 than adopt Mr. Salter's explanation, as given in the Introduction to 

 the Catalogue : — 



" This Chart is intended to show at a glance the developraent in 

 geological time of the different orders of the class Crustacea. Pic- 

 torial representations of the different groups of fossils, in their geo- 

 logical order, have been often before attempted, and the * Tabular 

 View of British Fossils,' compiled and engraved by Mr. Lowry 

 (published by the Society for Promoting Christian Knowledge), has 

 been conspicuously useful in this way. But we do not know of any 

 published Chart in which the relations of the different members of a 

 family or group are preserved in an unbroken series, so as to show 

 the course taken by that family or order of animals in the successive 

 geologic periods, from their first appearance to the present time. It 

 has been found practicable (due regard being had to size and shape 

 of the sections of the Chart) to arrange the species nearly in their 

 right natural-history order. This could not always be done, inas- 

 much as there are often members of the same genus in two geological 

 divisions. It has been thought best, therefore, in the Catalogue, to 

 follow the same order as that of the plate, that the student may the 

 more easily, in studying each group, follow it from its commence- 

 ment to its close. The rule followed is to take each group in 

 ascending order, from its commencement in the lower strata to its 

 close, or to modern times. The Chart shows through what length 

 of time any genus existed ; and it will be observed that comparatively 

 few genera (except among the small Bivalve Crustacea) range through 

 more than one or two formations. When it is otherwise, the student 

 has only to look in the Chart, at the next overlying formation, for 

 the members of the genus he is occupied with (and they are arranged 

 as nearly together as the space and other circumstances will allow), 

 and then, turning to the Catalogue, he will be conducted by it over 

 all the genera peculiarly characteristic of the lower formation before 

 proceeding to those of a higher one. Thus, for instance, in the group 

 Eurypterida he will find, in the Lower Silurian, that only foot- 

 marks of a gigantic species are known ; in the Upper Silurian, the 

 Hemiaspis and Bunodes are confined to that formation, while the 

 great Pterygotus aud Eurypterus are figured as reaching through 

 two formations. Consulting the Catalogue, he will find that Pteiy- 

 gotus problematicus\% an Upper Silurian species, and that P. anglicuSy 

 a very similar form, belongs to the Devonian formation. Again, 

 Eurypterus tetragonophthalmus is a Lower Devonian form ; but the 

 gigantic E. Hibberti belongs to the Carboniferous formation. One 

 or two in the Coal close the series. Here, then, the range of each 

 genus is extended through the formations to which it belongs. ,But, 

 in this particular case only, the size of the animals is so great that, 

 instead of figuring P. anglicus and P. problematicus one exactly over 

 the other, a single large figure is made to do duty for both. In all 

 other cases, as in the genus Limulus on the right hand of the chart, 

 or the genus Ilomalonotus or Calymene among the Trilobites, the 

 successive species are placed one over the other, and the range of the 



