Observations on the genus Rastrites and some allied species of Monograptus, 5 



species the theca? and the interne-dés only at a great distance from the sicula attain 

 their full size ; it can easily be inferred that distal fragments of one species may 

 be mistaken for proximal pieces of another. To this should be added that, owing 

 to lateral pressure, even complete specimens, at many localities, have been distended 

 in one direction and compressed in another to such a degree as to resemble 

 species quite different from those to which they really belong. Most of these diffi- 

 culties may certainly be surmounted if a sufficient number of examples from the 

 same locality and the same horizon are obtainable, but this is far from always 

 being the case. 



This paper, therefore, should be regarded only as a preliminary essay towards 

 unravelling the more distinguishable forms of Rastrites that have come under 

 my notice. And I have thought it not inappropriate, in connection with the 

 account of my researches into that genus, to add some observations on a few spe- 

 cies of Monograptus which in their appearance approch, more or less, to the 

 Rastrites. 



The material upon which the following observations are founded consists for 

 a great part in collections made by myself in different provinces of Sweden, in 

 England, Scotland, Bohemia, and Thuringia. To Mr. Robert Eisel, of Gera, I 

 am further indebted for a valuable collection of Thuringian graptolites, which he 

 was so kind as to present to me several years ago. As this collection was intended 

 to form an illustrative supplement to a paper published by him in 1899, and en- 

 titled »Ueber die Zonenfolge Ostthüringischer und Vogtländischer Graptolithenschie- 

 fer» l ), I have cited this paper in the lists of synonyms given in the sequel; and 

 in stating the zones of the Thuringian species, I have followed the zonal arrange- 

 ment proposed by Mr. Eisel 1 ). For the assistance offered to me by the keeper of 

 the Geological Museum of Lund, Professor J. C. Moberg, in using the collections 

 of the museum, I owe him my best thanks. 



1 ) Communicated to »39 bis 42 Jahresberichte der Gesellschaft von Freunden der Naturwis- 

 senschaften in Gera (Reuss) 1896—1899», Gera 1899. — Compare also: R. Eisel, Nachtrag zum 

 Fundortsverzeichnisse wie zur Zonenfolge thüringisch-vogtländischer Graptolithen; the cited Trans- 

 actions 1900—1902; Gera 1903. — The zones referred to in the sequel are (in ascendiag order): 

 Zone 12 a, Zone of Monograptus triangulatus 

 » 12 b, » » Rastrites peregrinus 

 » 13, > > Diplograptus (Cephalograptus) cometa 

 » 14, » » Rastrites Linnœi 

 » 15, » » Monograptus exiguus 



