1869.J The Treasures of Siluria. 33 



Species of one 



Groups. Total Species. Locality. 



Plautss 82 47 



Amorphozoa 136 92 



Foraminifera 25 



Coelenterata 507 220 



Ecliinodermata 500 365 



Annelida 154 m 



Cirripedes 8 6 



Trilobita 1611 708 



Entomostraca 318 198 



Polyzoa 441 265 



BiacLiopoda 1650 699 



Monomyaria 168 87 



Dimyaria 541 287 



Pttropoda 358 210 



Gasteropoda 895 454 



Cephalopoda 1454 858 



Pisces 37 26 



Incertae sedis 12 10 



8897 4620 



The total resuU is tliiis seen to be that more than half of 

 the known Silurian species have hitherto been found in only one 

 locality. This fact alone is sufficient to remind us (what Dr. 

 Bigsby quotes) that so thoughtful a naturalist as the late Professor 

 Edward Forbes asserted that a large proi^ortion of all known 

 species of fossils are founded on single specimens. 



It is a very remarkable fact that the species which are thus 

 restricted to a small geographical area are also those which attain 

 a small vertical range. Thus, in Bohemia, in two small and adjoin- 

 ing parishes near Prague, we find huddled together no less than 

 112 species of Cyrfoceras, 27 of Trochoceras, and 30 of Orthoceras, 

 with many other fossils, all of which are confined to one stratum, 

 and none of which have hitherto been found elsewhere. 



At the present day large assemblages of species (though their 

 value as such is doubtful), of one class of animals exist in certain 

 regions. For instance, the rivers of North America have yielded 

 countless forms of Unionidae, and those of Brazil (according to 

 Professor Agassiz) no less than 2000 species of fish. These " com- 

 munities," as Dr. Bigsby calls such poj)ulations, had their parallel 

 in Silurian times in Bohemia ; for there, in the wonderful deposit 

 E.e.2, which we have already mentioned, no less than 921 sf)ecies 

 have been discovered in a bed about 150 feet thick, extending over 

 an area not more than 15 miles long by 7 broad. Of this 

 large number, 590 species belong to the order Cephalopoda, 

 and of them no less than 220 species are pecuhar to one parish 

 (Lochkov), and 102 to another (Kozorz), while 75 others are 

 common to the two. These 590 species represent only 9 genera, 

 Orthoceras including 252 species, Cyrfoceras 199, Gompliocera^ 

 VOL. VI. r> 



