SUESS^ — DISTRIBUTION OF THE BRACHIOPODA. 



287 



I presume that the bathymetrical distribution of the great groups 

 of Brachiopoda has ever been nearly the same as it is now, viz., the 

 species with a translucid shell being confined, or nearly so, to the 

 higher zones, and those with opaque shells living in the deeper parts 

 of the sea. It is not necessary to enumerate the numerous cases in 

 which fossil Lingulidas and Discinidos have been found, together with 

 ripple-marks, littoral shells, or other signs of shallow sea ; nor to 

 point out how rare it is to meet with other Brachiopoda in such con- 

 ditions. But I must beg you to remember how very predominant 

 hornlike shells of Brachiopoda are in sandstone and shale, and how 

 marked the maxima of Rhynchonellidse, SpiriferidcB, TerebratulidjB, 

 &c., are in limestone, and more especially in argillaceous limestone. 

 It is a gross error to believe that these families are so frequently 

 wanting in sandstones or shales, because these latter have been 

 formed by a sea too poor in lime for the formation of these shells. 

 MM. Logan and Hunt have taught us that the shells of Lingulse also 

 consist principally of hme. I believe that the extinct family Spiri- 

 feridee ranges, as I have just remarked, with the other families with 

 opaque shells ; but as to the Strophomenid83 you will see that excep- 

 tions are somewhat more numerous, most of them belonging to the 

 (restricted) genus Ortliis. And now let us cast a glance on the dis- 

 tribution of a number of Silurian Brachiopoda, and for the sake of 

 shortness let us call all Lingulidas and Discinidee the Group A, and 

 all other Brachiopoda the Grotojo B, the genus Orthis and a number 

 of other Strophomenidas being regarded as standing between these 

 groups, Orthis, as you will remark, often offering a very marked 

 tendency associating with group A. 



In looking, as a first example, at M. Barrande's newest list of 

 primordial fossils in the Bulletin Soc. Geol. xvi., 1859, p 516 — 546, 

 you may find the following Brachiopoda : — Eight species of Lingula, 

 two Obolus, three Discina, five Orthis, and one doubtful Atrypa. 

 This can only be Atr. inicula (Dalne), oy Atr. lenticularis (Dalne),the 

 first of which, according to M. Barrande, approaches to Obolus or Lin- 

 gula. The latter surely is one of the Strophomenidse, and probably an 

 Orthis, So you see that this fauna only offers thirteen or fourteen 

 members of the group J., and five or six forms of the genus Orthis. 

 I cannot helieve that this association of Brachiopoda has lived in deep 

 water, and you know that the predominant rocks in which they are 

 found are sandstones and slates. 



In this case it is possible to attain a marked conclusion even in 

 contemplating the primordial fauna of all regions in which it has 

 been found as a whole, but for further studies it is necessary to 

 regard one country after the other. I will select a few examples 

 now, but must, before T do so, say that a part of the conclusions 

 at which I have arrived has been anticipated in a very nice way 

 by the statement of Mr. Sharpe (Quart. Jour, 1848, iv., p. 158), 

 that the genera Lingula and Orbicula, now preferring shallow 

 water, do not ofier identical species in the Silurian beds of 

 North America and Europe. I beg you to read the passage of 



