LOCALITIES AND SPECIES PER LOCALITY 



431 



I^UMBER OF LOCALITIES AND NUMBER OF SpECIES PER LOCALITY IN THE 

 DIFFERENT TyPES OF SeDTMENT 



Table V. — Groups of Cambrian and related Ordovician Brachiopoda giving 

 the number of localities and the number of species per locality in the dif- 

 ferent types of sediment. 





Number of localities. 



1 Average number of 

 species per locality. 



Groups, 



Total. 



Shale. 



Sand- 

 stone. 



Lime- 

 stone, 



Shale. 



Sand- 

 stone. 



Lime- 

 stone, 



A. — Lorality Nos. 1-300 ( U. 8. 



National Museum ) 



B.— Locality Nos. 300-396z (Lit- 



erature) 



703 



642 



35 



192 



170 

 12 



189 



241 

 



322 



231 

 23 



2.15 



1 55 

 1,75 



2.77 



1.70 

 



2,81 

 1,73 



C. — Chinese localities 



1.96 







The groups into which this table has been divided require a word of 

 explanation. Group A, numbers 1 to 300, includes collections that have 

 been made by members of the United States Geological Survey and the 

 United States National Museum at various times and under differing 

 conditions since the organization of the museum. With few exceptions 

 each represents a distinct faunule, definitely numbered, and all of the 

 brachiopods were culled for the work on the Cambrian Brachiopoda. 

 Group B, numbers 300 to 396z, represents miscellaneous collections in 

 the United States National Museum to which locality numbers have 

 never been assigned and occurrences mentioned in the literature. The 

 numbers have been arbitrarily assigned, there is no certainty that each 

 number, represents a distinct faunule, and in the case of the localities 

 taken from the literature there is hardly the probability that all of the 

 brachiopods occurring at each of the localities were described. Group C, 

 the collections made by the Carnegie Institution of Washington Expedi- 

 tion to China, is probably the best of the three for the purposes of this 

 study, since all of the collections were made by one man, under more or 

 less similar conditions, during a single field season; yet sandstones are 

 entirely unrepresented. Moreover, the forms from each of the groups 

 (Group B containing the only specific occurrences that have not been 

 checked by actual examination of the specimens themselves) have been 

 studied under more or less uniform conditions by the same specialists. 

 Among these three groups there appears to be no uniformity of ratio 

 between the number of localities in each of the three classes of sediment 

 and the total number included in the group. For the first two groups 



