320 Viscount (I'Archiac and M. de Verneuil 



only species that has been hitherto met with in the four quarters of the globe. Among 

 the ten Devonian and Carboniferous species, we may notice the 8p. oblata (Sow.), 

 as being found in Ireland, England, Belgium, the Eifel, and as occurring in Van 

 Diemen's Land; likewise the Sp. glaber, Sow., over all Western Europe and in 

 the state of Ohio. The three species which are met with throughout the entire series 

 of ancient deposits are, the Sp. octoplicatus, Sow., the Sp. crispus, Dalm., and the 

 Sp. striatulus, Schlot., but the S. striatulus is extremely rare. 



The Pentameri are hitherto exclusively Silurian. This genus is largely repre- 

 sented in the Ural chain, and species different from those of Europe are distributed 

 from Bogoslofsk in the north to Bielozeskoi in the south. {April 1842.) 



The Strygocephali, on the contrary, are peculiar to the Devonian system, and 

 the S. Burtini (Bronn) is very characteristic of its beds on the right bank of 

 the Rhine and in Devonshire. These shells appear to be very rare in the strata of 

 the same age so highly developed in Russia, for we have found only a single in- 

 dividual in the Ural. 



We have retained provisionally the name oi Atrypa for those shells which have not 

 yet been placed in any other genera, but it must be acknowledged that this group 

 is not zoologically well characterized, and that its distribution in the three systems 

 is but of minor interest : twenty-six Silurian species occur in England and Scan- 

 dinavia ; twenty-one Devonian are found in the south-west of England, as well as 

 eight which belong to the Carboniferous system. 



The TerehratulcB, as we have already mentioned, are almost equally distributed 

 through the three systems in Europe ; there are fifty Silurian, forty-nine Devonian, 

 and forty-four Carboniferous. This near equality of distribution is maintained in 

 relation to such of them as are common to two systems, for there are thirteen 

 which are both Silurian and Devonian, and ten Devonian and Carboniferous. 

 The greater part of the TerehratulcB peculiar to the Silurian system are from the 

 border counties of England and Wales, as well as from Scandinavia, and some are 

 found in Esthonia, Ingria, south of St. Petersburg, and in the province of Bolivia. 

 Conrad does not admit the existence of a single true Terebratula in the Silurian 

 system in the United States ; but we must remark, that this zoologist cites shells 

 under the name of Atrypa, which, in our opinion, are true TerehratulcB, and which 

 have in general been regarded as such down to the present time. 



In the middle system the TerehratulcB abound, particularly in Devonshire and in 

 the Eifel, on the right bank of the Rhine, and in the limestones of Elbersreuth. 

 Among the species peculiar to this system, the T.ferita, and the T. concentrica of 

 de Buch, are very characteristic in Devonshire, the Bas Boulonnais, the Coten- 

 tin, Belgium, the Eifel, the environs of Cologne and Russia : one of the most 

 interesting in Russia is the T. Meyendorfii, nob., which is very abundant on the 



