HISTORY OF RESEARCH. xxxvii 



Although M'Coy places the dichotomously branching forms provisionally in the 

 genus Diplograpsus, he points out that they constitute a " peculiar little group ; " 



and he suggests that if necessary they might be called Didymograpsus = t win 

 Grraptolites. This generic name is now in general use for a certain section of these 

 two-branched forms, namely, for those which have their simple, sub-cylindrical, 

 tube-like cells on the inner margin. 



In the second edition of Murchison's ' Siluria,' published 



in 1854, a brief description of four genera of Grraptolites, viz. 



. ,' Diplograpsus, Graptolites, Eastrites, and Didymograpsus, is 



given, with figures of a few of the most characteristic species 



in illustration. 



Murchison does not commit himself to any opinion as to the zoological affinities 

 of the Graptolites, but merely points out that they have been supposed by some to 

 be nearly allied to Virgularia, the Corallines or Sertularia, and he considers that 

 they " grew on the fine mud at the bottom of the sea." 



As regards their geological range, he asserts that they are exclusively Silurian, 

 and that in Britain neither Diplograpsus nor Didymograpsus are "ever met with 

 above the horizon of the Caradoc sandstone;" in Bohemia, however, the double- 

 celled Diplograpsus occurs in association with the single-celled form Graptolites. 



In the year 1855 Professor R. Harkness described but 



did not figure a neAV species of Graptolite under the name 

 Harkness 



"A tl •• 'f gvt Rastrites Barrandi, from the Glenkiln shales of the Moffat 



and Fucoidal Remains country. Judging from his description, this may have been a 



in the Lower Silurian form of Thamnograptus. Many Graptolite species are recorded 



Rocks of the South of by ] imi \ n this paper from various localities in South Scotland, 



co anc , guar . including Gr. Sagittarius, Diplog. pristis, J>. ramosus, IK m/ucro- 



, .' natus, and D.oicomis, D. folium, dr. Sedgwickii, R. peregrinus, 



and B. Lii/mvi. 



In the light of recent opinion as to the mode of life of the Graptolites, it is 



interesting to note that Harkness makes the same suggestion as that already made 



by Suess (1851) ; viz. that the carbonaceous matter of the anthracite shales has 



not been derived from the Graptolites themselves, but is " due to the existence of 



seaweeds during the earlier portion of the Lower Silurian epoch." 



1855. 

 Cassiano de Prado, 

 " Sur la geologie 



d'Almaden d'une ^ n the same year Cassiano de Prado recorded Gr. spiralis, 



partie de la Sierra Gr. Halli, Gr. priodon, and Gr. palmeus from the Silurian 

 Morena and des rocks of Almada, the Sierra Morena and Toledo. 



Montagues de Toledo," 

 ' Bull, de la Soc. geol. 

 de France,' vol. xii. 



