STUDY OF THE GRAPTOLITES. 269 



SUPPLEMENTARY NOTES. 



REMARKS UPON THE GENERA DIDYMOGRAPTUS M'COT, CLADOGRAPTUS Geinitz, CLADO- 

 GRAPTUS Carruthers, DICRANOGRAPTUS AND CCENOGRAPTUS Hall. 



In 1851, Prof. M'CoY {British Palmosoie Fossils, page 9) suggested the 

 name Didymograptus in the following manner, after describing Diplo- 

 graptus ? sextans Hall, sp. : 



" From the strong aiEnity between this and the D. furcatus Hall, sp. I 

 provisionally leave it in the present genus, though it differs much from the 

 normally formed species. Those species, l)ifid from the base as this, the serra- 

 tulus Hall, murchisoni Beck, etc., form a little group, having one row of cells 

 on each branch, sometimes on the inner, and sometimes on the outer edge: if 

 necessary, these might be called Didymograptus — the twin graptolites." 



The term Didymograptus as adopted in Great Britain, has usually 

 been applied to such forms as G. murchisoni and G. serratulus ; but Prof. 

 M'CoY clearly included species of two very distinct types, since G. sextans 

 and G. furcatus have a different mode of growth, the cellules being on 

 the outer margin of the polypary, and of a different form from those of the 

 first named species and others usually referred to Didymograptus. 



In 1852, Prof Geinitz* proposed the name Cladograptus, which, in 

 its definition, included also the two groups of species here noticed, viz : 

 those with the cellules angular and on the inner margin of the stipe, and 

 those with curving indentations upon the outer margin of the stipe. He 

 cites C. ramosus and C. furcatus Hall sp., in his first group, and C. mur- 

 chisoni Beck, C. serra Geinitz, C. forschammeri Geinitz, C. sextans and C. 

 serratulus Hall sp., in his second group. We have in fact precisely the 

 same grouping under Cladograptus that M'Coy has given under Didymo- 

 graptus. If the latter term be employed to designate such forms as G. 

 murchisoni Beck, G. serratulus and G. bifidis Hall, and similar forms, then 

 Cladograptus may be used in the restricted sense to designate such forms 

 as G. furcatus, G. sextans and G. divaricatus Hall. In this case the term 

 Dicranogkaptus might be dropped ; since it may not be proper to sepa- 

 rate those with the stipe partially divided from those entirely divided, 



* Die Versteinerungen der Grauwacken formation in Sachsen, etc. Heft 1, Die Chaptolithen, 

 pp. 29-32. 



