NIABARA GROtrP. 249 



BRACHIOPODA OF THE NIAGARA GROUP. 



We find at this period large numbers of individuals of this family of fossils, though of com- 

 paratively few species. There is a manifest diminution in the number of species of Lingula, 

 Orthis and Leptcena ; while we observe an increase among those of Spirifer and Atrypa over 

 similar forms in the Lower Silurian period. This change, which was noticed in the Clinton 

 group, becomes more conspicuous in the Niagara period ; showing not only a continuannce, but 

 an increased intensity, of those causes which operated through successive periods of time, as 

 manifested throughout the palseozoic era. 



We have comparatively few new species among those which have fallen under observation, 

 most of them having been published in this country or in Europe. We find in this family, as 

 well as in others, that the fossils of the Niagara group correspond so closely (many species being 

 identical) with those of the Wenlock limestone of Great Britain, that we can not hesitate to 

 regard the two formations as synchronous. This geological parallel is in fact almost the only 

 one that we can regard as fully established, except for the great groups below this, when taken 

 together ; for we are not able to identify them individually. Neither are we able to identify 

 the succeeding formations, except in a very general way. From some facts developed in re- 

 lation to the succession of groups in this country, it would seem that we have, in a succeeding 

 limestone and shale, another representation of the Wenlock formation, as these rocks are almost 

 a repetition of the Niagara group. This formation, consisting of the limestone bearing Penta- 

 merus galeafus, and of the " Delthyris shaly limestone," though separated from the Niagara 

 group by many hundreds of feet, and in fact containing scarcely one fossil found in that group, 

 seems to be, in Great Britain and elsewhere in Europe, merged in one formation with the 

 Wenlock. Therefore it may appear that the fossils of the Niagara group will but imperfectly 

 represent those of the same period in Europe ; and it will only be when we have brought 

 together, in a succeeding volume, those of the higher rocks, that a full comparison can be 

 made. 



437. 16. LINGULA LAMELLATA. 



PL. LIII. rigs. 1 and 2. 

 Lingula lamellata. Hall, Geol. Rep. 4th District, 1843, pag. 108, fig. 2 ; descr. p. 109. 

 Oval, somewhat broader at the base ; surface marked by concentric elevated lamellae ; lamella 

 slightly undulating ; shell sometimes wrinkled at the margins ; base rounded. 



Fig. 1. A specimen preserving the shell, and having the beak acute. 



Fig. 2. A specimen where the shell is removed, leaving the surface with faint concentric lines 

 and a few longitudinal striae. 



[PALiEONTOLO&Y — VoL. II.] 32 



