HISTORY OF RESEARCH. lxv 



(7) Tn the Wenlock Gr. Flemingii is characteristic; Eetiolites Geinitzianus 

 occurs here, l>ut also in the Lower Silurian and the Ludlow; Gr. priodon and 

 Gr. minim* occur in the Wenlock and in the Lower and Upper Ludlow; Ptilograpsus 

 is peculiar to the Lower Ludlow. 



In spite of the apparently wide range in time of nearly all the species and 

 genera cited, Nicholson remarks that they afford " very reliable and valuable data 

 whereby formations in different parts of the world may be correlated with one 

 another, or the exact position held by any group of beds in the stratified series may 

 be more or less exactly ascertained," an assertion which, however slightly founded 

 at that time, has been shown by subsequent research to be practically correct. 



18 gg During the same year, 1 868, and previous to the publication 



Garrwthers, of some of Nicholson's papers mentioned above, Carruthers 



" Eevision of the brought out his 'Revision of the British Graptolites,' with 



British Graptolites, descriptions of several new species and notes on their 



with Description of „, ., ■ 



1 affinities. 



JNew bpecies and 



Notes on their ^ D * ne classincatory part oi tins paper a large number of 



Affinities," ' Geol. species are described, and the new ones (sonic of them previously 



Mag.,' vol. v. mentioned by him in his appendix to Murchison's 'Siluria,' 



Edit. 4) are figured and described. 



The genus Bastrites, as acknowledged by him, includes four species : 

 E. peregrinus, (1) E. Linnsel, (2) E. maximus, and a new form (3) 11. capillaris. 

 He holds that II. triangulatus (Hark) was founded on the proximal part of 

 Gr. convolutus (Monograptus), and he gives a figure showing that this species 

 of Graptolite "really terminates proximally in a polypary which cannot be 

 distinguished from that of Bastrites," thus throwing doubt on the stability of the 

 genus Bastrites itself. He points out that E. Barrandei (Hark) was founded on 

 fragments of Cladograpsus (Goenograptus) gracilis. 



The genus Graptolithus he restricts in the same manner as other palaeon- 

 tologists of the time to forms now classed as Monograptus. He considers that 

 this generic term ought properly to be applied to double forms like Gr. scalaris 

 (Linn), for which it was first employed by its founder, but that it would create too 

 much confusion to make the correction now. Graptolithus is represented by twelve 

 species in his list: Gr. Nilssoni, Gr. Flemingii, Gr. tenuis, Gr. Salteri, Gr. Hisingen, 

 (4) Gr. convolutus, Gr. Sedgwickii, Gr. priodon, Gr. Halli, Gr. BecJci, (5) Gr. Glingani 

 and a new species, (6) Gr. intermedins. His own new genus, Gyrtograpsus 

 (previously named in 'Siluria'), is described, and his species (7) C. Murchisoni 

 is re-figured. He shows that 0. hamatus (Baily) also belongs to this genus. 



He does not regard the number of branches in allied forms of Graptolites 

 as a generic distinction, and therefore includes under Didjjmograpsus species of 

 Tetragrapsv.s, as well as forms of Dicellograpsus. lie considers that "the 

 possession of an obvious branching hydrocaulus stipe " might be a good reliable 



