INTRODUCTION. 



In his classical work »Les Graptolites de Bohême», published in the year 

 1850, Bareande divided the Silurian graptolites of Bohemia into three genera, viz. 

 Gladiolites or Retiolites, Graptolithus and Rastrites. The last genus was established 

 to embrace such uniserial graptolites as were characterized by isolated, cylindrical 

 thecse; whereas both uniserial and biserial forms were included in the genus Grapto- 

 lithus if their thecrc were in contact with each other. The single-rowed species were 

 referred to the sub-genus Monoprion, the double-rowed, to the sub-genus Diprion. 

 Already in the following year Suess restricted the genus Graptolithus so as to com- 

 prise only uniserial species, but, at the same time, he withdrew Barra nde's genus 

 Rastrites, regarding the species referred to it as constituting merely a sub-group of 

 Graptolithus 1 ). In 1852 Geinitz proposed to substitute the name Monograpsus, in 

 later times altered to Monograptùs, for that of Graptolithus; and, as regards the 

 genus Rastrites, he adopted the views advanced by Suess. As an argument for 

 this conception he adduced the existence of such a form as Monograptus triangu 

 latus Harkn., which, according to his interpretation, was proximally a Rastrites, 

 and distally a true Monograptus 2 ). Suess looked upon Barrande's genus Rastrites 

 as representing a poorly developed group of Monograptus, Geinitz regarded it as 

 a degenerated group of the same 3 ). Richter has in several papers accepted the 

 nomenclature insisted on by these authors 4 ). Still as late as 1890 Geinitz maintains 

 his earlier opinion 3 ), but the majority of later authors who have written on grapto- 

 lites, are at one in admitting the validity of the genus Rastrites. 



The close resemblance that exists between the two genera now under con- 

 sideration is, no doubt, undeniable, and especially do some helicoid Monograpti in 

 their proximal parts show a puzzling approximation to the earlier forms of Rastri- 



') E. Suess, Über Böhmische Graptolithen, Wien; p. 6, 23. 



2 ) H. B. Geinitz, Die Versteinerungen der Grauwackeformation in Sachsen und den angren- 

 zenden Länder Ahtheilungen; Heft. 1. Die Graptolithen, Leipzig 1852; p. 19, 47. 



3 ) E. Suess, loc. cit. p. 5. — H. B. Geinitz, Die Graptolithen des K. Mineralogischen Mu- 

 seums in Dresden; Mittheilungen aus dem Koenigliclien Mineralogisch-Geologischen und Prähisto- 

 rischen Museums in Dresden, Neuntes Heft, Cassel 1890; p. 31. 



4 ) R. Richter, Zeitschrift der Deutschen Geologischen Gesellschaft, Bd V, 1853; Bd XXIII, 

 1871; Bd XXVII, 1875. 



