REVIEWS 471 



geologist to give close attention to the fossil faunas present in his rock 

 formations, and to have accurate identifications of his fossils. It is, 

 therefore, a pleasure to notice the appearance of such a work as North 

 American Index Fossils by Grabau and Shimer. 



In the two volumes of 853 and 909 pages respectively which com- 

 prise this work, approximately 1,500 genera and 4,000 species are 

 defined, a large portion of the species being accompanied by illustrations 

 incorporated in the text, the figures being copied from various sources 

 for which credit is always given. The species selected for definition 

 have been chosen to include, first, those most characteristic of impor- 

 tant stratigraphic divisions, i.e., those of wide geographic and limited 

 stratigraphic range; secondly, those having a wide geographic distri- 

 bution even though their stratigraphic range is also great, i.e., the very 

 common American species; and thirdly, forms which it is important 

 that students of structural and anatomical paleontology should under- 

 stand. The species are arranged chronologically under their respective 

 genera, the genera being arranged systematically under their proper 

 families, orders, classes, and phyla. Brief discussions of the structural 

 features of each phylum and class are included, but except in the case 

 of the Arthropoda, no definitions of subclasses or orders are given. 

 Under each class is given a brief bibliography of the more important 

 literature, which will be of use to such as wish to carry their studies 

 beyond the limits of the work. A decided innovation is the inclusion 

 of extensive analytical keys to the genera under each of the classes. 

 These keys are probably the most elaborate ever attempted for fossil 

 invertebrates, and will doubtless be of much value to those using the 

 books, although it must be kept in mind always that such keys can 

 never be of so great utility in the classification of fossils, which are fre- 

 quently if not usually represented by more or less incomplete speci- 

 mens, as in the classification of living organisms. 



The closing pages of the second volume are given up to a series of 

 appendices, as follows: A, Summary of North American Stratigraphy, 

 Tables of Geological Formations (50 pages); B, Faunal Summary, 

 Tables Showing Distribution of Species Described (50 pages); C, 

 General Bibliography of North American Invertebrate Index Fossils 

 and Fossil Faunas (183 2-1 909) (89 pages). In this bibliography the 

 titles are arranged in accordance with the geological systems, those for 

 each system being grouped geographically; D, Hints for Collecting and 

 Preparing Fossil Invertebrates (16 pages); E, Glossary (36 pages) and 

 General Index. 



