xvi BRITISH GRAPTOLITES. 



belonging to the Diplograptids. The species which he refers to as GraptoUthus, 

 sp., seems to be Barrande's Bastrites peregrinus. 



In his second gronp {straight or double-toothed Graptolites) Richter includes 

 four species: (3) Gr. folium ; (4) GraptoUthus, sp., for which he suggests the new 

 name Gr. mucronatns (a name already preoccupied) ; (5) Gr. priodon, of which he 

 gives no figure, and which he thinks might belong to a third group — the dosed 

 Graptolites; and (G) G. scalar is, under which he apparently includes the two forms 

 usually known in recent years as Glimacograptas normaUs and G. rectangularis. 



The figures given by Richter are for the most part good, and show well the typical 

 graptolitic structure. He notices such details of structure as (1) the alternating 

 arrangement of the cells in double Graptolites, a character which he considers 

 invariable ; (2) the thickening of the wall at the aperture ; and (3) the prolongation 

 of the virgula (or the " siphon," as he calls it) in a proximal direction. This last 

 phenomenon he holds may be explained either by the fact that the cells have 

 dropped off, or that they were very small during life. 



Richter notes that the species of Graptolites described were all obtained by 

 him from the Silurian formation of the Thiiringer "VVald, in the neighbourhood of 

 Saalfeld, but gives nothing as to their further range or geographical distribution. 



CHAPTER II. 



Second Pekiod, 1850 to 1865. 



1850. 



In the year 1850 appeared Barrande's epoch-making work 

 Barrande, on the ' Graptolites de Boheme.' This added so largely to 



' Graptolites de our previous knowledge of the Graptolites, and was marked 



Boheme. throughout by such an admirable method of treatment, sim- 



plicity and clearness in the presentation of the facts, and brilliance of inference 

 and generalisation, that it gave an impetus to their study, the importance of 

 Avhich can hardly be over-estimated. The work is one of much detail, and it 

 will be best to discuss it in the order of arrangement that Barrande himself 

 adopts. 



General Sections. 



1. Nature of the Gra,ptoHtes. — Barrande considered that the evidence he had 

 himself accumulated as to the nature of the Graptolites Avas strongly opposed to the 

 view held l)y the majority of })revious observers, namely, that the Graptolites were 



