C. Schuchert — Russian Carboniferous and Permian. 157 



the ever-recurring disputes concerning Lower Silurian, Cam- 

 brian, CambrO'Silurian, Ordovician, or Chain plain. 



5. Tschernyschew lays great stress upon the occurrence of 

 a form of the brachiopod family Lyttoniidse in the Schwagerina 

 horizon of the Urals. Certainly it has great faunal value, but 

 the acumen of Tschernyschew also led him to note the fact 

 that it is not of the Indian genus Lyttonia ( '= Leptodus ) . 

 To it he gave the generic name Keyserlingina, and the few 

 involutions of the brachia indicate that it has not yet progressed 

 to that degree of specialization shown in the brachia of the 

 Indian genus Lyttonia. In other words, Keyserlingina holds 

 a lower stratigraphic horizon than Lyttonia. In the Austrian 

 Alps, another primitive form of the Lyttoniidse is found, but 

 here the brachial folds are not laterally directed as in the other 

 forms, but anteriorly. Hence, it is not in the direct line of 

 evolution with the Indian genus, which has also been discovered 

 in Xevada and at El Paso, Texas (Dr. Girty states that he 

 also has it from the Robinson beds of California). The reviewer 

 therefore believes that while Keyserlingina unmistakably indi- 

 cates that the Schwagerina fauna is of the Asiatic type, it is 

 less highly specialized than Lyttonia, and consequently holds 

 a lower geological horizon. 



6. In regard to Tschernyschew's conclusion that the Russian 

 Permian brachiopods show " atavistic trends, 1 ' the writer does 

 not think it is borne out by the facts. A list of the species is 

 given on page 31. All of the forms occur below either in the 

 Artinsk or the Upper Carboniferous. In fact all are persisting 

 or long-lived species and are therefore not atavistic in any 

 phylogenetic sense. The brachiopod fauna of the typical 

 Permian, however, may be said to be atavistic in aspect 

 because all of the progressive forms of the Artinsk have failed 

 to continue into this formation. 



7. The reviewer, from his knowledge of the late Paleozoic 

 brachiopods, is confident that this class of fossils can be relied 

 on for detailed correlation of stratigraphic horizons over widely 

 separated regions, and further on account of their persistence 

 and wide distribution they are among the best evidence for 

 facial affinity. The Carboniferous and Permian brachiopods 

 are given too great specific latitude by many paleontologists, so 

 that it is common in the literature of the subject to note that 

 many species are found on more than one continent. Pro- 

 ductus semireticidatus is believed to occur throughout all Car- 

 boniferous time and is common to the world. Such a condi- 

 tion permits of no exact correlation. 



8. The writer can not see that the evidence as presented by 

 Tschernyschew breaks down the laboriously attained conclu- 

 sions of "Waagen, j^oetling, and Diener, that the Productus- 



