Geology and Mineralogy. 563 



brachiopods along modern lines will be conducive to better pale- 

 ontologic work in Europe. 



Holtedahl here monographs all of the Ordovician and Silurian 

 strophomenids found in southern Norway, 74 in number, of which 

 55 are named specifically. Of new species or varieties there are 

 22, and one new genus, Palmostrophomena (1 species). Of 

 American genera there are Kafinesquina with 22 forms, Brachy- 

 prion 5, Leptostrophia 2, Strophomena 18, Amphistrophia 2, Stro- 

 phonella 1, Schuchertella 1, Leptsena 5, Plectambonites 13, 

 Christiania 1, Triplecia 2, and Streptis 1. We therefore learn 

 that the generic development in America and Europe is almost 

 identical, but in regard to the species the story is very different. 

 There are only 8 forms that are certainly known to be common 

 to the two continents (there may be 11), and of these 4 are ubiqui- 

 tous [Schuchertella pecten, JLeptcena rhomboidalis, Plectambon- 

 ites sericeus, and P. transver salts). The 6rst intercommunication 

 of species, but to a very limited extent, occurs in the Middle 

 Ordovician (Black River-Trenton), with a more liberal inter- 

 change in late Ordovician (Richmondian) and more especially in 

 early Silurian time. In Europe the relationship in the earliest 

 Ordovician is between Norway and western Russia, and then the 

 exchanges in late Ordovician and Silurian times are between Great 

 Britain and Norway. 



The strophomenids of Norway and Russia begin in earliest 

 Ordovician time in but few species, with small individuals. 

 Plectella may be the progenitor of the family, and with it are 

 soon associated Ratinesquina, Palmostrophomena, and possibly 

 one or two other as yet undetermined genera. The first marked 

 evolution takes place early in the Middle Ordovician with a more 

 decided generic variation in latest Ordovician and earliest Silurian 

 time. 



Holtedahl has also grouped the species according to the kinds 

 of rocks in which they occur, and we learn that the strophomenids 

 in the main are lovers of clear seas depositing limestone. Of the 

 common species, 36 are restricted to limestones, 3 to shales, and 

 12 occur in both habitats. The mud-lovers are usually the ubiqui- 

 tous forms and the long-lived species are those that are adapted 

 to varying habitats. Finally, there is on page 10 of the paper a 

 valuable correlation table of the Ordovician and Silurian strata of 

 Norway and western Russia. c. s. 



2. A revision of the Cheirurince with notes on their Evolution ; 

 bv Donald C. Barton. Washington University Studies, Vol. 

 Ill, Pt. I, No. 1, 1915, pp. 101-152, 25 text figs.— This valuable 

 revision of cheirurid trilobites treats of 20 genera, of which 3 are 

 new : Pilekia, Kawina, and JLehua. The subfamily may have 

 had its origin in late Cambrian time, though none are known 

 earlier than the Lower Ordovician. In the Middle Ordovician 

 occurred the greatest amount of evolution, but four genera are 

 known in the Silurian, and none appear to have endured into 

 Middle Devonian time. The Cheirurinse are therefore essentially 

 Ordovician animals. c. s. 



