Geology mid Natural History. 445 



because the author, following Smith Woodward, refers to this 

 sub-class the Arthrodira. The test for relationship the author 

 finds in the jaw of Arthrodires, for it conforms "strictly to the 

 Dipnoan type, a fact of cardinal importance for their classifica- 

 tion." c. s. 



2. The Paleontology of the Niagaran Limestone in the Chi- 

 cago Area. . The Trilobita ; by Stuart Weller. Nat. Hist. 

 Survey, Chicago Acad. Sci., Bull, iv, pt. ii, 1907, pp. 163-281, 

 pis. xvi-xxv. — Professor Weller gives here a complete account 

 of the Silurian trilobites of the Chicago area which extends 

 from Milwaukee, Wisconsin on the north, south to Joliet, Illinois. 

 There are 41 species and of these 19 are new. There is also one 

 new genus, Illaenoicles. The detailed stratigraphy is not yet 

 determined but four horizons are recognized in the dolomites, 

 seemingly ranging from the Clinton well up into the Guelph. On 

 pages 181-210 a complete bibliography is given of all North 

 American species of trilobites, of which there are 105. The 

 illustrations are good, being photographic reproductions of crayon 

 work on stipple paper. c. s. 



3. Revision der Ostbaltischen Silurischen Trilobiten • Abh. 

 VI, von Fr. Schmidt. Mem. Acad. Imp. Sci. St. Petersbourg, 

 xx, No. 8, 19(»7, pp. 104, pis. 3. — This extensive and valuable 

 work, treating of the Ordovician and Silurian trilobites of the 

 eastern Baltic region, begun thirty years ago by the author, is 

 now completed. In this part a general review of the work is 

 given, supplementing the old species with such information as 

 has been gleaned from new material and such changes as are due 

 to the interaction of the workof others during the interim. In 

 1858 Estland, Livland and Osel had furnished Schmidt fifty 

 species. Since 1876 he has made known from these and the St. 

 Petersburg regions 256 species or varieties, and of these he has 

 named about 105 forms. From the Lower Cambrian there is but 

 a single species, Olenellus mickioitzi. The next ti'ilobite zones 

 are to be correlated with the American Stones River and Chazy 

 formations of the Middle Ordovician and from these and the 

 Upper Ordovician horizons there are not less then 229 forms. 

 Not a single one of these passes into the Silurian, a fact of far 

 greater significance in the Baltic region than in America because 

 of the many prophetic species of the marine invertebrates in the 

 higher Ordovician beds of Estland. Of Silurian species there are 



•26 (the Swedish island, Gotland, alone having 76) and 6 of these 

 are cosmopolitan forms, ranging as far south as Ireland and Eng- 

 land. Of the southern European faunas there is but one in 

 common with Bohemia, Deiphon forbesi. 



Of the 229 western Russian Ordovician species, at least 64 are 

 also found in Sweden or Norway. The close proximity of these 

 regions leads one to look for a greater number of forms in com- 

 mon than is here indicated. As there was then, seemingly, no 

 land barrier between these regions, and as the fossils show that 

 all belong to one marine province, the discrepancy must be 



