77 



form, a type almost unknown in the Lower, but very prolific of species in 

 the Middle and Upper Silurian. This group becomes extinct in the 

 Devonian. The genera Favosites, Heliolites and Helopora which here 

 first appear in force, are more characteristic of the upper than of the 

 lower half of the Silurian series. Most of the other new species belong to 

 the ordinary Silurian genera. 



The fauna of this Division is partly Lower and partly Middle Silurian 

 but is more strongly tinged with the former than the latter. 



Division 2. — From this Division we have only 39 species of which 18 

 are received from Division 1, and 21 here first made their appearance. 

 Out of the whole fauna 23, or more than one half pass into Division 3 and 

 16 into Division 4. As before stated, the only species very characteristic 

 of the Lower Silurian are Strophometia alternataa,nd 3Iarc]iisonia gracilis. 

 The most prominent fossil is Pentamerus Barrandi which occurs in 

 vast numbers. Owing to the inaccessible character of the coast in bad 

 weather, it was not practicable to make a thorough search for fossils in this 

 Division. 



Division 3. — In this Division there are 53 species, of which 23 are 

 received from Divison 1, and 26 pass upwards. We here meet for the 

 first time with Pentamerus ohlongus, Strieklandinia lens, S. lirata, iS. 

 brevis and Laptocoelia hemispherica. These are all strongly characteristic 

 of the Middle Silurian and occur in this Division and also in Division 4 

 in great abundance. 



Division 4. — There are 70 species from this Division, of which 26 are 

 received from below. 



Conclusion. 



The great abundance of such species as Strophomena rhom.hoidalis. 

 S. pecten, S. antiquata, Leptcena transversalis, Orthis Davidsoni, 

 Pentamerus oblongus, Strieklandinia lens, S. lirata, S. brevis, 

 Oyrtia Myrtea, Spirifera jjlieatella and JOeptocadia hemispherica, 

 together with the general aspect of the whole fauna of divisions 3 

 and 4, render it quite certain that this part of the series repre- 

 sents the Upper Llandovery rocks of England, and, perhaps, the 

 Lower Llandovery also. They may not be exactly synchronous, for it 

 seems to be now pretty conclusively demonstrated that a fauna may appear 

 somewhat earlier in one region than in another. But, so far as we can 

 at present decide the question by fossil evidence, these rocks are of the 

 same age. I use the word fauna in a purely zoological sense, with no 

 reference to geographical distribution. With regard to the Llandovery 

 formation, Mr. Salter makes the following remarks ; — " The Lower Llan- 

 dovery, or, as I prefer to call it, with Professor Phillips, the Llandovery 

 rocks, ^^ are intimately united with the Caradoc, and pass up from them 



