Vol. 56.] 



SHALES OF THE WELSH BORDKKLAND. 



403 



length. Length of sicula = y 1 ^ inch (1*587 mm.). Outer wall 

 curved, inner straight. Thecae closely set throughout, numbering as 



many as forty-four to the inch (seventeen 

 in 10 mm.) near the sicula. The rhabdo- 

 soma widens very rapidly to a maximum 

 width of j inch (3*174 mm.). 



Fi 



R- 13.- 

 var. y 



M. Flemingii, 

 from the M. 

 Irfon and Ackley. 



f 



[Nat. size.] 



Fig. 14. — M. Flemingii, 

 var. 3, from the Irfon. 



Var. a. (Text-fig. 14.) 

 An exceedingly long form, often at- 

 taining a length of 7 or 8 inches 

 (175 mm.). The whole rhabdosoma is 

 irregularly curved, and decidedly so near 

 the proximal end. The rhabdosoma 

 widens slowly up to a maximum of -Jq inch 

 (2*54 mm.). The number of thecee varies 

 in different parts of the rhabdosoma, but 

 is never less than twenty -four to the inch 

 (nine or ten in 10 mm.). 



Var. a makes its first appearance in 

 the zone of Cyrtograptus symmetricus 

 (where it is very rare), and attains its 

 maximum development in the zone of 

 G. rigidus, where var. fi appears. 



Var. (3 is never a common form, but 

 it is also found in the succeeding zone. 

 The characteristic little variety y is 

 practically confined to the base of the 

 C.-Lundgreni zone, and is very abun- 

 dant there ; while var. c), which appears 

 at the same time, attains its maximum 

 development in the higher parts of that 

 zone, and is very occasionally to be met 

 with at the base of the Lower Ludlow. 



The accompanying table (IX, p. 404) 

 illustrates the chief characteristics of 

 these varieties. 



MONOGRAPTUS V0MEBINU8 (Nich.). 



Nicholson, 'Monogr. Brit. Graptolitidae ' 1872, 

 p. 53, fig. 21 ; Lapworth, ' Scottish Monograptidae ' 

 Geol. Mag. 1876, p. 353 & pi. xii, figs. 6 a-e ; 

 Tullberg, ' Skanes Graptoliter ' pt. ii (1883) Sver. 

 Geol.Undersokn. ser. C, no. 55, p. 19 & pi. ii, tigs. 10- 

 11 ; Perner, ' Etudes sur les Graptolites de Boheme ' 

 pt. iii, sect, b (1899) p. 18 & pi. xiv, figs. 2 a-c & 

 fig. 20, pi. xvi, figs. 1-3, pi. xvii, fig. 13. 



There appear to be three graptolites of the type of Monograptus 

 vnmerinm (Nich.) present in the zone of C yrtograptus Murchisoni, 

 though the third has not been found by me in the districts 

 with which this paper deals. 



[Nat. size.] 



