J. H0PKIN80N ON BRITISH GRAPT0LITE9. 157 



McCoy, in the same year, raised tliese sections into genera, 

 altering the name Diprion to Diplograpsus, and retaining the 

 original name Graptolithus for the section Monoprion. In the 

 following year he established the genus Didymoyrapsus for species 

 having two simple branches. 



Hall, in 1857, described a remarkable form with four series of 

 hydrothecfe, naming it Phyllograptus. In 1865, he proposed three 

 new genera — Dendrograptus, for species branching and re-branching 

 from a thick hydrocaulus ; Climacograptus, for species having a 

 double series of hydrothecas excavated in the margin of the poly- 

 pary ; and Dicranograptus, for species having a single and double 

 series of hydrothecae on the same polypary. 



In 1858, Carruthers proposed the name Cladograpsus, for species 

 growing irregularly in two directions from the radicle, and re- 

 peatedly branching ; and in 1867, Cyi^tograpsus, for species re- 

 peatedly branching in one direction from the radicle. 



In 1861, Salter proposed the name Dichograjysus, for species 

 having many branches growing bilaterally from a central disc ; and 

 in 1863, Tetragrapsus, for species having only four branches. 



Nicholson has recently (1867) added the synonym Pleurograpsus 

 to the genus Cladograpsus, Carr. 



§ III. Classification. 



In a series of papers in Sir E. Murchison's " Siluria" (ed. 1867) ; 

 in the " Intellectual Observer " (May and June, 1867) ; and in the 

 " Geological Magazine " (February and March, 1868), my friend, 

 Mr. William Carruthers, groups all British genera of graptolites 

 into four sections. The genera of Section I. have a single series 

 of hydrothecae ; of Section II., a double series ; of Section III., a 

 single and double series ; and of Section IV., a quadruple series. 



In a paper read before the Geologists' Association last April, I 

 proposed to consider these sections sub-orders, or rather families, 

 and named them respectively — IlonojJrionidce, Diprionidce, Mono- 

 diprionidce, and Tetraprionidce. The family Monoprionidce cor- 

 responds to Barrande's section Monoprion (including Rastrites), and 

 the family Diprionidce to his section Diprion. 



The following is an arrangement of the British genera. It 

 differs but little from that of Mr. Carruthers. 



