HISTORY OF REHEAIUMl. xxi 



12. Disfi'ihiifiov (if (ir(ipfoHti-A ill Fiirciipi Goniiirioj^. — Rafraiidc disciisscs the 

 (|uestinii of tli(> tit'iKM-al disd'ibiitioii of (ii-aptolitcf^ at coiisidci'alik' Icn^tli, and i^ivcs 

 tlic I'osnlt of tlio I'csearclics of all ])i'('vious writei'S as to their raiii^c. Alllion^li lie 

 colloctod all the material obtainable on this subject, he content(d himself with 

 general remarks as to the range of the Clraptolites in time and space. His 

 conclnsions may be snnnned up as follows : — Graptolites belong- characteristically 

 to the Silurian system ; in England they made their appearance during the 

 period marked by the primordial fauna of Bohemia, reaching their maxinmm 

 development about the middle of the Silurian period, — that is to say, at the top of 

 the Lower and base of the Upper Silurian ; and dying out altogether in the Lower 

 Ludlow beds. 



Descrlptirc Sections. 



After giving a historical summary of the literature of the sul)ject, Barrande 

 devoted the rest of his memoir to the description of the various Bohemian genera 

 and species. Both the descriptions and the illustrative figures given by Barrande 

 were far in advance of anything done previously by graptolithologists, and the 

 descrij^tive letterpress of his work has remained a standard type for diagnosis down 

 to the present day. Several of the beautiful figures upon his illustrative plates, 

 however, are, in accordance Avith the practice of the time, either generalised from 

 more than one specimen, or somewhat idealised in the matter of detail. 



But the state of knowledge of specific characteristics was then naturally inferior 

 to that of the present day, and some of his species included forms now acknow- 

 ledged to be specifically distinct. Thus under the name GraptoHtlms priodon 

 (Bronn) l^arrande not only included Bronn's typical form (PI. I, figs, o, 5 — 9), 

 but at least three other forms also, which are now usually regarded as belonging 

 to distinct species, viz. Giirtogniptus MurcJiisoni (Carr.), Monograptus spiralis, var. 

 suhconicus (Tullb.), and Mono. Jaelcell (Perner, ' Etudes sur les Graptolites de 

 Boheme,' part 3). Again, the illustrations of his own species Gr. cohmus embrace 

 those of three distinct forms, of wdiich the most characteristic (PI. II, figs. 2 and 3) 

 is now by common consent regarded as that of the type species, while fig. 5 may 

 probably be assigned to the form at present classed as Mono, duhius of Suess, and 

 figs. 1 and 4 to Mono, vomer inus of Nicholson. Perhaps the most conspicuous case 

 is that of his Gr. Nilssoni, which he illustrates by three figures. Thesea re drawn as 

 if the specimens represented occurred together upon one and the same slab of rock, 

 but they are now known to have been obtained from different localities and from 

 different horizons (Perner, op. cit.). Fig. J 6 is now regarded as the type form of 

 Gr. Nilssoni; fig. 17 as a specimen of Gyrto. Lnndgreni ; wliile fig. 18 belongs to 

 Gijrfo. tv.Jndiferns of Perner. 



The species of Graptolites identified, described, and figured by Barrande include 

 the (1) Mono, priodon and (2) Mono, spiralis of earlier authors, and the following 



