366 Graptolites. 



on the family is introduced, and he retains the word according 

 to the original Linnaean spelling, in which he is followed by 

 writers abroad. Under this name all the numerous and varied 

 forms were included which had been described by Hisinger, 

 Murchison, Portlock, Hall, Geinitz, and others. 



Barrande, in his valuable memoir on the graptolites of 

 Bohemia (1850), first subdivided the genus. He established 

 the new genera — Rastrites, for species with the cells separated 

 by distinct interspaces on a slender axis (Plate I., Fig. 17; 

 Plate II., Figs. 9 and 10), and Retiolites for a somewhat anomalous 

 form without a central solid axis (Plate I., Fig. 12). He further 

 divided the restricted genus Grcvptolithus into two sections, the 

 one Monoprion, characterized by possessing a single series of 

 cells (Plate II., Figs. 1, 3, 7, etc.), and the other Diprion, 

 having a double series of cells (Plate II., Figs. 2, 4, 5). 

 M'Coy in the same year gave these sections a generic value, 

 retaining the original name for Barrande' s Monojprion group, 

 and proposing the name Diplograpsus for the species included 

 in the section Diprion. 



Barrande, accepting Hisinger's determination, considered 

 the Priodon Sagittarius of that author the same as Grarptolitkus 

 Sagittarius, Linn., and consequently held the species with a 

 single series of cells to be the true Linnaaan type of the original 

 genus. He further endeavoured to show that G. scalaris, Linn., 

 was a " scalariforni" impression of a single-celled species, and 

 by an oversight which is remarkable in a work specially 

 characterized by the careful and accurate observation that 

 distinguishes all the labours of its illustrious author, he 

 figures a double- celled graptolite as the " scalariform" im- 

 pression of two single-celled species, viz. : G. nuntlus, Barr., 

 and G. Haiti, Barr., as has been already pointed out by Hall. 

 M'Coy, influenced by similar considerations, erroneously re- 

 tained the Linnasan generic designation for the single-celled 

 forms. Were it not that he has been invariably followed, I 

 would venture to restore the name given by Linnasus to the 

 only form with which he was acquainted ;' but this would intro- 

 duce into the accepted nomenclature so many changes without- 

 corresponding advantages, that the strict application here of 

 the law of priority would scarcely be justified. 



Suess, in 1851, added the synonym Petalolithus to M ; Coy's 

 genus Diplograpsus. 



In the same year M'Coy further separated a well-marked 

 group of species, in which the polypary consists of two simple 

 branches, from his restricted genus Graptolites, for which ho 

 proposed the name Didymograpsus (Plate II., Fig. 12), and in 

 I lie following year Geinitz applied the title Gladograpsus to the 

 same. Unaware that this name had been employed, I pro- 



