AMPHIGRAPTUS. 121 



It is commonly associated with Leptog. fiaccidus and its varieties, Diplog. truncatus, 

 and other Diplograpti of the " foliaceus " type. There are good specimens in the 

 collections of H.M. Survey, the Woodwardian (Sedgwick) Museum, the British 

 Museum, and in the private collections of Lapworth and the Authors. 



Var. simplex, Lapworth MS. Plate XVII, fig. 2. 



Description. — This variety of Pleurog. linearis is one in which the main stipes 

 have usually a wider sweep, and in which the secondary branches, which are 

 simple, are few in number, generally only three on each main stipe; their 

 disposition, moreover, is more regular than in the typical form, there being about 

 1*5 cm. between each branch. 

 „ ,. The sicula in the tvpe specimen gives rise to a 



Iiu. i2. — Plen n><j rii pins linearis, var. •/ i i o 



simplex, Lapw. MS. central stipe or branch. 



- - The thecas agree in all particulars with those of 



the typical form. 

 Thecae of main stipe near proximal end. . „ n , „ 



Enlargement of part of pi. xvii, Horizon and Locality. — llartrell Shales (zone ol 



Pleurog. linearis). 



S. Scotland : Hartfell Spa. 



Associates, etc. — Var. simplex occurs in some abundance in the Hartfell Shales 

 in the zone of Pleurog. linearis, associated with the zone fossil and various Diplo- 

 grapti. The type specimen is in Lapwortli's collection, and there are others in the 

 Authors' collections. 



Genus AMPHIGRAPTUS, Lapworth. 



1873. Amphigraptus, Lapworth, "Notes on the British G-raptolites and their Allies," G-eol. Mag., 

 vol. x, p. 559. 



Polypary rigid, bilaterally subsymmetrical, consisting of two uniserial main 

 stipes, diverging from the sicula at an angle of approximately L80 , which 

 give off regularly or irregularly disposed, rigid, simple or compound 

 secondary branches constituting a more or less radiate polypary. 

 Thecae of the characteristic Leptograptus type, with low inclination and small 

 amount of overlap. 

 The Amphigraptus polypary is characterised by the straightness and rigidity of 

 both stipes and branches, and their approximately radial disposition. 



The main stipes are, generally speaking, narrow, but they vary in width from 



