C. Lapworth — On Scottish Monograptidce. 309 



Thuringia — have not as yet afforded Graptolites. They occur, 

 however, in abundance in the succeeding Eiccarton beds, and a few 

 have also been obtained from the more recent deposits of the 

 Pentland Hills. 



3. Vertical Bange of the Monograptidce. — In the present memoir I 

 shall treat of the species of Hhabdophora already collected from 

 these Scottish rocks, which belong to the family of the Mono- 

 graptidcB. Several of these have been figured and described by our 

 British palaeontologists, — M'Coy, Harkuess, Salter, Carruthers, 

 Nicholson and Hopkinson. It is only lately, however, that the 

 vertical range of many has been definitely ascertained. Others 

 again have been erroneously identified, some imperfectly figured or 

 described, while several new species await notice, and the whole 

 subject stands in need of a thorough revision. 



The Graptolites included in the family of the MonograptidcB 

 — which embraces the three genera Bastrites, Barr., Monograptus, 

 Geinitz, and Cyrtograptus, Carruthers — are confined exclusively to 

 the Middle and Upper Silurian rocks. Not a single example has 

 hitherto been detected in strata inferior in geologic position to the 

 Bala Limestone of North Wales. Several forms from more ancient 

 deposits have indeed been classed by palaeontologists under Graptoli- 

 tlius (^Monograptus) , but there now appears to be sufficient evidence 

 to prove that they were all in reality merely disjoined fragments of 

 compound Graptoloidea. The British and Continental strata, long 

 known as affording in great abundance species truly belonging to 

 the family, were formerly assigned to the epoch of the Lower 

 Silurian on insufficient evidence, and are now known to appertain 

 either to the Llandovery or to the true Upper Silurian. 



The range of the genus Monograptus is included between the 

 horizons of the Bala and Aymestry Limestones. Cyrtograptus has 

 nearly the same vertical distribution. The genus Rastrites seems to 

 be strictly confined to the Llandovery, and is wanting even in the 

 highest and lowest beds of that formation. 



4. Distribution of the Monograptidce in Scotland. — In Scotland the 

 Monograptidce make their first appearance in the Birkhill Shales 

 (Upper Moffat). In the underlying deposits of the Middle and 

 Lower Moffat beds they are wholly wanting. Striking evidence of 

 this restriction is afforded by the circumstance that in the numerous 

 anticlines in the districts of the Lammermuirs, Moorfoots, Leadhills, 

 etc., where the Birkhill Shales are absent, not a single Monograptid 

 has yet been detected in the highly fossiliferous Moffat Series ; while 

 in the Ettrick, Moffat, Dumfries, and South Wigton districts, where 

 the Birkhill beds are present in force, they swarm innumerably. 

 These Birkhill Shales not only exhibit the advent of the family, 

 but also afford tolerably conclusive evidence of its specific 

 culmination, — the overlying groups showing a great falling 

 off both in species and individuals. The very numerous forms 

 afforded by these Birkhill Shales allow us to parallel the sub-forma- 

 tion exactly with similar deposits in the North of England, Ireland, 

 Thuringia, Bohemia and Scandinavia. Monograptidce occur also, but 

 in much less abundance, in the carbonaceous beds found near the 



