408 Dr. 0. Herrmann — Distribution of Oraptolites. 



simply constructed, the uniserial and one-sided Monograptidge, figur- 

 ing also as the oldest representatives of the group. He will wonder 

 to see the Graptolites suddenly make their appearance in the world 

 of organisms under complicated and yevy elegant forms. 



The oldest Graptolite family, Dichograptidfe, Lapw., appears 

 therefore, as we have already seen, in the uppermost division of the 

 Cambrian, attains the maximum of its development in the lowest 

 division of the Lower Silurian (Arenig formation), and becomes 

 extinguished before the superior limit of the Lower Silurian is 

 reached. 



The next oldest family, Phyllograptidfe, Lapw,, appears to be con- 

 fined to the lowest division of the Lower Silurian (Arenig). The 

 same is the case with the family LasiograptidEe, Linnars., or Glosso- 

 gi'aptidfe, Lapw., with its still partly problematical forms of Lower 

 Silurian age. The Leptograptidse, Lapw., and Dicranograptidte, 

 Lapw., are also confined to the Lower Silurian. The most ancient 

 representatives of both families make their appearance in the lowest 

 division (Upper Arenig), and the most modern are extinguished in 

 the uppermost division (Upper Caradoc) of the Lower Sihirian. 



The family Diplograptidse, Lapw., commences with isolated species 

 as early as the lower limit of the Lower Silurian, but is fully deve- 

 loped only at its upper boundary and extends up into the Upper 

 Silurian, although it dies out completely in the first division of this 

 (Valentian). 



The vertical distribution of the family Eetiolites coincides with 

 that of the preceding famil3\ 



All these families are followed, after the most luxuriant period of 

 this group of animals is passed, and it is already rapidly declining, 

 by the Monograptidse. "With regard to these Lapworth has shown 

 that, contrary to previous notions, they are strictly confined to the 

 Upper Silurian, and that therefore, according to the present stand- 

 point of our knowledge of the Graptolites, " the mere presence of a 

 single species of the Monograptidse may at once be set down as con- 

 clusive evidence of the (Upper) Silurian age of its containing beds." 

 This family, as already indicated, is survived only by the genus 

 Bictyograptus, Hopk., which passes into the Devonian. Bictyograptus, 

 Hopk., is at present still unranged in the system.' 



Passing from these brief remarks upon the distribution of the 

 Graptolites in time, to their distribution in space, or geographical 

 distribution, we must mention at once that our organisms are cosmo- 

 politan fossils. Up to the present time we have been able to ascer- 

 tain their existence in the Silurian deposits of three continents, 

 Europe, America, and Australia. 



In Sweden, where these fossils were first observed, we have to seek 

 the localities for Graptolites in the districts of Schonen, West and 

 East Gothland, Dalecarlia, and Jemtland, and in Gotland. The best- 

 known names of these may be here given in order to facilitate the 



^ S. A. Tullberg's most recent work (Zeitschr. d. deutsch. Geol. Gesellscli. 1883, 

 pp. 223-269) contains a system in which the Dictyograptidse, Tullb., are placed, as a 

 new family, at the head of all other families. 



