Vol. 56.] FOBMATION AND ITS GRAPT0L1TE-FATTNA. 457 



Monograptus vulgaris is of considerable palaeontological interest, for 

 it possesses characters which ally it both with the M.-dubius and the 

 M. -colonus groups. This is well seen, not only in the shape of the 

 thecce, but abo in the character of the proximal end : the first theca 

 being inclined to the sicula at a low angle as in M. dubius, yet 

 arising above the aperture as in M. colonus. 



Localities. — This species occurs most abundantly in the Long 

 Mountain district, but I have also found it at Builth, and Miss Elles 

 has recognized it in the Dee Yalley. 



Horizon. — M. vulgaris is the characteristic graptolite of the 

 lowest zone of the Lower Ludlow. 



Associates. — M. dubius and Betiolites nassa. 



M. vulgaris has a considerable range in time, and undergoes 

 certain modifications as we follow it higher up the succession. 

 If the specimens of M. vidgaris were in a more satisfactory state 

 of preservation, I believe that it would be possible to trace the 

 gradual stages in the evolution of this species, from the type-form 

 at the base of the succession, through the various horizons of the 

 Ludlow Shales, to the well-marked varietal forms at the top. Two 

 distinct varieties characteristic of the higher horizons may be here 

 distinguished. 



Var. a nov. (PI. XXV, fig. 3.) 



This variety is distinguished from the typical form by 



(1) The shape of the adult thecae, which are relatively broader and only 



3 times as long as wide, and therefore more distant ; 



(2) The general shape of the polypary, which is straight distally and more 



incurved proximally, and seldom, if ever, exceeds 5 cm. (2 inches) 

 in length. 



Localities. — Long Mountain (Trefnant-Middletown Brook, etc.); 

 Ludlow district (Elton Lane?). 



Horizon. — Zone of M. Nilssoni. 



Associates. — M. Nilssoni, M. uncinatus var. orbatus, M. colonus 

 var. compactus, M. varians. 



Yar. fi nov. (PI. XXV, fig. 4.) 



This variety is distinguished from the typical form by 



(1) Its greater narrowness, the maximum width rarely attaining 2 mm. 



(•08 inch) ; 



(2) The general form of the polypary, which has a strong proximal curva- 



ture and straight distal portion ; 



(3) The character of the proximal end : the sicula is nearly 5 times 



as long as wide, and the first theca appears to arise rather nearer 

 the sicular aperture ; 



(4) The form of the thecse: they are shorter and narrower, and their 



apertures appear to be slightly oblique to the direction of the thecse. 



It occurs on the north side of the Long Mountain, at Lane Farm, 

 in association with M. bohemicus, in the zone of M. Nilssoni, or 

 possibly in the sub-zone of M. Eoemeri. 



