620 HISTORICAL GEOLOGY. 



The earliest of known fossil insects is from Graptolitic slates iu the upper 

 part of the Lower Silurian of southern Sweden. It is a Hemipter, and is 

 named by Moberg Protocimex Siluricus (1892). 



729. 



Telson of Ceratiocaris Angelini, nat. size. Jones and Woodward, ' 



Characteristic Species. 



Great Britain. — Arenig group. — The Skiddaw slates of the Arenig group abound in 

 Graptolites of the genera Diplograptus, Climacograptus, Didymograptus, Phyllograptus, 

 Denclrograptus, etc. Other prominent genera and species of the group are : Orthis calli- 

 gramma, Oholella plicata, Lingulella Davisi; Pleurotomaria, Ophileta, Baphistoma; 

 Bellerophon, Conularia Homfrayi, Orthoceras; Agnostus, uEglina grandis, Ogygia, 

 Asaphus Homfrayi, Amp)yx Salteri ; also the new genera Trinucleus, Illcenus, Barrandia, 

 Calymene, Phacops, Plaropai'ia, Humolonotus. 



Llandeilo flags and Loiver Bala. — Graptolites of the same genera as in the Arenig j 

 also Halysites catennlatus, Monticulipora favulosa, Favosites fibrosiis ; Actinocrinus, 

 Echinosphoerites, Glyptocrinus, Palaeaster ; Acrotreta, Crania, Leptcena, Strophomena, 

 Bhynchonella; Modiolopsis., Ctenodonta, Palcearca, Pleurorhynchus (Conocardium),. 

 Ophileta compacta, Murchisonia bellicincta, Euomplialus, Loxonema, Pleurotomaria ; 

 Orthoceras., Bndoceras, Piloceras ; Ogygia Buchii, Asaphus tyrannus, A. Poioisi, Ampyx 

 nudus, Barrandia, Trinucletis, Acidaspis Jamesii, Lichas, Blcenus, Homalonotus, Cheiru- 

 rus, Phacops, Calymene Bhimenbachii, ^glina mirabilis. 



Bala beds, Caradoc sandstone, and Coniston limestone.-^ Monticulipora frondosa M., 

 Favosites fibrosus, Heliolites interstinctus, Halysites catennlatus, Cyathophylluni, Petraia ; 

 Leptcena rhomb oidalis, Orthis biforata, O. caUigramma, 0. flabelluhim, 0. porcata, 

 0. elegantula, Atrypa imbricata, Leptcena (Plectambonites) sericea, Crania divaricata ; 

 3Iurchisonia, Holopella, Trochonema, Baphistoma, Cyclonema, Bellerophon bilobatus, B. 

 nodosus, B. carinatus (which three species occur also in the Lower and Upper Lland- 

 overy) ; Orthoceras vagans, 0. annulatum, 0. Barrandii (the three continuing into the 

 Lower Llandovery) ; Endoceras, Lituites, Cyrtoceras, Trocholites, Piloceras; Elcenus, 

 Phacops, Cheirurus, Lichas, Acidaspis, Ampyx, Agnostus, Harpes, Bemopleurides, Caly- 

 mene Bhimenbachii, C. Allportiana, Sphcerexochus minis. 



Lower Llandovery group. — Favosites fibrosus, Halysites catennlatus, Heliolites inter- 

 stinctus, Petraia bina, Orthis Bouchardi, Atrypa, Meristella subundata, Stricklandinia 

 lens, Bhynchonella tripartita, Spirifer plicatellns, S. exporrectus, Strophomena arenacea, 

 Pentamerus oblongus, P. undatus, P. globosus (the three occurring in the Lower and 

 Upper Llandovery) ; Blcenus Bowmani, Cheirurus bimucronatus, Trinucleus concen- 

 triciis, Proetus Girvanensis. Lower Silurian beds occur in the south of Scotland, and 

 also in the northwest Highlands. But in the latter region there is a striking resemblance 

 in fossils, as pointed out by Salter, to forms in Canada and New York — the species includ- 

 ing Orthoceras arcuoliratum, Orthis striatula, Ophileta compacta, Blurchisonia gracilis, 

 M. bellicincta, and also species of Maclurea, Baphistoma, and others of American type. 

 Moreover, at the same time, the species of northwestern Scotland differed from those of 

 England and Wales. From these facts it is evident that troughs with Archajan confines- 

 had the same importance on the British or European border of the Atlantic as on the 

 North American side. We may conclude also that the barrier between northwestern Scot- 



