vi BRITISH GEAPTOLITES. 



Walilenbci'g describes the occurrence of similar Graptolites also in Dalecarlia (at 

 Osmundsberg and Furudal), and notices cai'efully the various conditions of 

 preservation in which they ai'e found. " In the shale of Scania, Avliich always has 

 a black colour, the Graptolites occur as impressions with a certain peculiar lustre, 

 or when pyrites is present are rusty, and at the same time they are occasionally 

 found as solid bodies filled up Avitli pyrites." These, he contends, " show clearly 

 the nature of Orthoceratites." 



In addition to Linngeus' G. scalarls, Wahlenberg also notices the occurrence of 

 certain one-sided forms which he erroneously refers to Linnteus' G. Sagittarius. 

 According to the Swedish geologists, the form identified by Wahlenberg with G. 

 Sagittarius is probably identical with the species subsequently named Monograptns 

 leptotheca by Lapworth. At any rate, it is quite clear that it is not the same as 

 Linnseus' G. Sagittarius (see aiite). He holds that there is but little doubt that these 

 one-sided forms have their origin from the same minute Orthoceratites by a peculiar 

 kind of decomposition. " Some of these Orthoceratites, which had a siphon or a 

 lateral nerve, seem to have curved themselves after the destruction of the opposite 

 wall, and so to have produced lines on one side like the points of an arrow." He 

 considers that these arrow-like structures, which are curved, have arisen from the 

 " interlocular dissepiments." 



The result of Wahlenberg's work was to call general attention to these fossils, 

 and the observers who succeeded him found no difficulty in recognising the organic 

 remains thus fixed as " Graptolites," and they employed the term strictly in 

 Wahlenberg's sense. 



1322 The views of Walch and Wahlenberg, with respect to the 



VoH ScMothelm, Ceplialopodous nature of the Graptolites (as thus restricted 



' NachtrJlge zur Petre- by Wahlenberg), were adopted by von Schlotheim, who, in 

 faktenkunde; pt. ii. ;^g22, described and figured a Graptolite under the name 

 Ortlioccratites serratus. It is impossil)le to identify this species with certainty from 

 Schlotheim's figure, but the " haarformige Nervenr()hrc," which he notices running 

 down the back of the fossil, is almost certainly the structure now known as the 

 virgula. This form was obtained from the shales of Andrarum. According to von 

 Schlotheim, his species is the same as that described by Schroter inhis 'Einleitung,' 

 Til. iv, but we have not been able to gain access to Schrciter's paper. 



1828. Von Bromell's primitive idea of the vegetable origin of 



Brongniarl, these curious fossils, however, was not relinquished by all 



'Histoire rles pahrontologists, and in 1828 Brongniart described and figured 



Vc'gt<taux Fossiles.' ^^^.^ ^^^^ g^^^-g^ ^^^ Graptolites from the limestone of Pt. Levis, 

 under the names of Fiicoides serra and /''. dentatus. The former is the species 

 of T(',tragra,j)tus Avliich was subsequently described by Hall as T. hrgonoides 

 (' Graptolites of the Quebec Group,' 1865), and the latter is a DiiAograftus 

 {D. dentatus). 



