378 



Br. J. J. Bigsby's Brief Account of the [Feb. 21, 



The Cephalopoda, Crustacea, Brachiopoda, and Annelida of Europe ap- 

 pear to largely exceed in number of species those of North America, while 

 in nine Orders (see Table C) the two hemispheres hold nearly equal quan- 

 tities. America greatly surpasses Europe in the number of its Crinoids, 

 and to a smaller extent in Plantse and Gasteropoda. I am not prepared 

 with any inference from these facts. We know that the mineral constitu- 

 tion, and the past external influences in these several parts of the earth 

 are different- — not that the first is as influential as has been supposed. 



Many species are marked as undefined in the ' Thesaurus,' because they 

 are often only known by simple fragments. 



About a thousand species have never been seen but in one locality. 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 Marmora and Mene- 

 ghini, have not hitherto produced a Trilobite ; nor has Spain given up a 

 Fentamerus, as far as can be learnt. Out of our sixty species of AsapJius 

 only one is known in Bohemia. Silurian fish are only mentioned as exist- 

 ing in Britain, Bohemia, and Russia ; but doubtless they are in other Silu- 

 rian areas. 



The Trilobite genus Bikelocejphalus 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 New- 

 foundland, although primordial, is thought to be without this remarkable 

 genus. 



Each of the twenty- seven known species of the Heteropod Maclurea is 

 confined to one spot ; twenty are American ; and of these, eleven are con- 

 fined 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 Konieprus and Mnienian. 



Out of 2/0 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 Fleurotomaria, 



On the other hand. Nova Scotia holds one^half of all our Cleidophora ; 

 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. 



