XVI 



FACTS AND OBSERVATIONS. 



Some information on the recurrency of this order may be had in the great Table on the subject 

 in page 191. 



BRACHIOPODA. There has been placed on page 126* a summary of the geographical distribution 

 of the Silurian Brachiopoda. It tells us that North America has yielded 1121 specific appearances, 

 and that Europe &c. has given 1672, a much larger number. Twenty-seven genera of this order are 

 common to the two worlds; eight are exclusively American, and fourteen are European. With 

 respect to the comparative numbers of species, the Table in page 126 is approximately correct, and it 

 enters into curious details on the species common to several widely separated countries. 



Almost all the genera are scattered freely; the richer, of course, very widely. It is interesting 

 in no ordinary degree to run the eye along the Table (p. 126*) from West to East, from Bolivia 

 (S. A.), or Rupert's Land in the north, through forty-one Silurian areas, and see that even now 

 there is an almost unbroken line of Orthides girdling the globe a . Other genera present a like 

 continuous belt of species passing from land to land round the world : we refer to Atrypa, Discina, 

 Lingula, Pentamerus, Rhynchonella, Spirifera, Strophomena. It is almost certain that the other 

 genera have a similarly wide range (Chonetes, Obolus, &c). The gaps are fast filling up. 



The Table (I) subjoined is intended to show the vertical distribution of the Brachiopodal species. 

 If this order can be said to be very characteristic of the Silurian epoch, it is from the some- 

 what equable manner in which the species are diffused over its four stages, especially those of the 

 larger genera. Eight rich genera appear in every stage, sometimes increasing in numbers from 

 below (Athyris, Atrypa, Rhynchonella, Spirifera, &c.), while others rather decrease, as Lingula, 

 Or this. 



TABLE I, showing the Vertical Distribution of the Silurian Brachiopoda (species). 



They are not so much massed in one or two beds as the Cephalopoda are in Trenton Lime- 

 stone, Pleta, or Fauna E. e. 2 of Bohemia. 



a The Table gives 37 as the number of countries inhabited by the Orthides ; but we now find it to be 41. Dis- 

 crepancies of this limited kind will be found elsewhere in the ' Thesaurus.' They are almost inseparable from the 

 progressive nature of the work, 



b Ehynchonella Corinthia. c Strophomena Aurora. 



