Dr. J. J. Bigsby on the ' Thesaurus Siluricus,' 295 



At least 200 Cyrtocerata are huddled together in the two contiguous 

 parishes of Lockhov and Kozorz, near Prague, and, with other 

 mollusks there, are unknown elsewhere. Other instances of this 

 might be cited. 



The two Silurian districts of Sardinia, with not a few fossils in 

 common with Spain, although tolerably well examined by La Mar- 

 mora and Meneghini, have not hitherto produced a Trilobite ; nor 

 has Spain given up a PentameruSy as far as can be learnt. Out of 

 our sixty species of Asaphus only one is known in Bohemia. Silu- 

 rian fish are only mentioned as existing in Britain, Bohemia, and 

 Russia ; but doubtless they are in other Silurian areas. 



The Trilobite genus Dikelocephalus of D. D. Owen contains 

 thirty species. Only three are found in two places. Twelve species 

 are near Quebec, and there only. Nine others are Minnesotan, 

 on the Upper Mississippi ; while the States of Texas and Vermont, 

 on Lake Champlain, have each one, and Wales three — all distinct 

 species. Western Newfoundland, although primordial, is thought 

 to be without this remarkable genus. 



Each of the twenty-seven known species of the Heteropod Mac- 

 lurea is confined to one spot ; twenty are American ; and of these 

 eleven are confined to Newfoundland West. 



Of the forty-five species of the genus Trochoceras (Cephalopoda), 

 forty-three are restricted to the vicinity of Prague ; and of these 

 twenty-seven inhabited the very small space of 4-6 square miles, in 

 company with many other mollusks. The Brachiopoda of Bohemia 

 are mostly in the Fauna F, and in, the two small districts of Konie- 

 prus and Mnienian. 



Out af 270 species of Orthis only two are believed to be in Nova 

 Scotia, and of the 109 species of the Gasteropod Murchisonia, again, 

 two, but not one of the elsewhere most abundant genus PleurotO' 

 maria. 



On the other hand. Nova Scotia holds one-half of all our Cleido- 

 phora; and Tasmania is singularly rich in Palcearca, while the 

 Point Levi shales are crowded with the Graptolite family, of extreme 

 beauty, and rarely found in other countries. We further observe 

 that, as it is with the horizontal disposition of Silurian life, so it is 

 with the vertical : only twelve per cent, leave their native horizon, 

 as we shall see. 



These few facts have been selected from many, to show the strong 

 tendency to localization inherent in the Silurian fauna. 



Primordial Stage* 



The * Thesaurus ' amply manifests the great extent of this stage, 

 and the high significance of its teachings ; but we shall here only 

 speak of a few leading facts relating to Canada, extracted from the 

 * Thesaurus' itself. 



While waiting for the results of field-work now in progress, Mr. 

 Billings has treated this subject with his usual great ability in the 

 first volume of the work entitled * The Palaeozoic Fossils of Canada.* 



21* 



