HISTORY OK RESEARCH. xciii 



thograpsus Granti, Ptilograpsus foliaceus, Thamnograpsus bartonensis, and 

 < •allograpsus niagarensis. 



187i). In I <S70 LinnarssoD described the various graptolite 



Lirmareson, horizons of Sweden, and compared them with those of Greal 



"Jakttagelser ofver .1- Britain and elsewhere. He recognises three main divisions: 



graptolitforande ^ Lq ^ Middl nd /g) g Graptolite 



skiffrarne i Skane, v ' . . 



' Geol. Foren Forh.' shales, corresponding in the main to (1) Arenig, (2) Llandeilo- 



uo. 50, bd. 4. Bartfell, (3) Llandovery to Lower Ludlow. 



187 In the same year Linnarsson described three species of 



Linnarsson. Graptolites from the Visby and Middle Gotland Groups el' 



" Om Gotlands the Silurian formation in Gotland. The Graptolites, though 



Graptoliter," ' Kongl. rare, are well preserved in limestone, and Linnarsson was 



Vetensk-Akad. Forh.,' ab]c t(j • (1( , t . |i|( , (1 descriptions of their structure, illustrated 



no. 5. , f. , , [ 



by excellent drawings. 



Structure. — In his description of Monogra/psus yriodon he calls attention to 

 the variation in form of the proximal portion of the polypary, as figured by 

 different authors ; and he inclines to the view that the straight shape is the more 

 typical. 



1879. An admirable summary and digest of the chief results of 



Zittel. research and opinion with respect to the Graptolites to the 



"Handbuch der cloge of tll0 ye;u . lg7 g wag given ))y Zitte ] j n t]lc second part 



gl (issued in 187 ( .>) of his ' Handbucb der Palseontologie.' He 



assigns the Oladophora (Hopk.) to the Campanulariae, and 

 classes the Rhabdophora (Allmann)as a distinct sub-order of the Hydroida, but under 

 the title of the Graptolithidse. The structure of the polypary in the ( Jraptolithidae is 

 described and illustrated; and the mode of existence and zoological position, etc., 

 of the Graptolites in general discussed. The classification adopted agrees 

 essentially with that of Lapworth (1873). The geological ranges of the various 

 genera are noted, and it is shown that six main Graptolitic horizons or zones are 

 already recognisable in Europe and North America. The text is illustrated by 

 several good figures. 



His observations on the structure of Eetiolites Geinitzianus are somewhat 

 indefinite, owing to the fact that he had only one specimen for examination. The 

 chitinous network he believes to be quite superficial, and the stronger strands 

 which mark the boundaries of the thecee probably mere threads, not lamellae as is 

 the case with other Graptolites, so that the interior of the polypary is not divided 

 up into separate thecse. No virgula was observed by him in this Gotland 

 specimen, and he is inclined to doubt the existence of two virgula? as described 

 by Barrande. A species of Viclyonema is also recorded by him, but is not 

 described or figured. 



