Vol. 56.] FOKMATION AND ITS GEAPTOLITE-FAUNA. 465 



to be worthy of varietal names. Helm Knot in Cumberland affords 

 examples of Monograptus colonus (PL XXV, fig. 10 b) which, of 

 all the British forms, bear the closest resemblance to the Bohemian 

 type. 



In the examples found at Adferton (PI. XXV, fig. 10 d) in the 

 Ludlow district (type-specimen M. Eoemeri, Lapw.), the polypary 

 appears to widen out rather more rapidly than usual, and the adult 

 thecae are somewhat longer in proportion to their width, being 5 

 times as long as wide. At Builth, where the species occurs in 

 great abundance, associated with M. Nilssoni, M. bohemicus, and 

 Metiolites spinosus, it seems rarely to exceed 3*1 cm. (l'2o inch) 

 in length, and the incurve at the proximal extremity is con- 

 spicuous. The thecae are close-set, thirty-four to thirty in 1 inch 

 (thirteen and a half to twelve in 1 cm.), and are long and narrow. 

 Occasionally, however, at Builth (PI. XXV, fig. 10 c), specimens 

 differing but little from the typical form may be found. In the 

 Long Mountain district the place of M. colonus is taken by another 

 form, which 1 think is sufficiently distinct to be described as a new 

 species. 



Foreign Localitie s. — Bohemia (Vyskocilka, Kuchelbad, Kozel, 

 Litohlav, Slavik, Butowitz, Borek, etc. ; Colonies Krejci, Tachlowitz, 

 d'Archiac, etc.): Scandinavia; Saxony; Thuringia ; Harz Mountains; 

 Polnisches Mittelgebirge ; Graptolithengestein ; France (Ardennes, 

 Languedoc, Normandy, and Britanny). 



British Localities. — Ludlow district (Elton Lane, Adferton); 

 Builth (River Irfon, etc.) ; Lake District (Helm Knot, etc.) ; Dee 

 Valley ? 



Horizon. — Zone of M. Nilssoni. 



Associates. — M. Nilssoni, M. boliemicus, and Retiolites spinosus. 



Var. ludensis (Murch.). (PI. XXV, fig. 11.) 



1839. Grajptolithus ludensis, Murcliison, ' The Silurian System ' p. 694 & pi xxvi, 

 fig. 2. 



M. ludensis was originally figured by Murchison, but no descrip- 

 tion was appended. Beck, to whom. Sir Roderick sent his specimens, 

 identified them with Swedish forms which he intended to name 

 Graptolithus virgulatus ; but Murchison adhered to his own name 

 of Or. ludensis. M'Coy, in his 'British Palaeozoic Fossils' (1855, 

 p. 4), described M. ludensis in terms which make it evident that 

 he was referring to M. priodon, and since that time M. ludensis 

 has generally been considered as synonymous with M. priodon. 

 Since the adoption of Bronn's earlier specific name priodon, the 

 name ludensis has gradually disappeared from use. 



It seemed clear, however, from Murchison's fig. 2, pi. xxvi, that 

 his specimens did not belong to the priodon-gvoa-p at all, and 

 when I was enabled to examine and draw Murchison's original 

 specimens in the Geological Society's Museum it was evident that 

 they belonged to a form closely allied to M. colonus. Since the 

 type-specimens were not well enough preserved to enable me to 



