32 BRITISH GRAPTOLITES. 



Didymograptus, ef. filiformis, Tullberg. Text figs. 20 a, h. 



1880. Didymograptus filiformis, Tullberg, G-eol. F5ren. i. Stockh. ForliandL, vol. v, p. 42, pi. ii, 



figs. 8—11. 

 1901. Didymograptus filiformis, Tornquist, Luncls Univ. Arssk., Bd. 37, Af. 2, Nr. 5, pi. iii, figs. 



6-9. 



Stipes very slender, not exceeding 127 mm. in leng-th, and Tvitli a uniform 

 width of about '5 mm., diverging at about 90° from a long and narrow 

 sicula. Thecse seven in 10 mm., inclined at 20°, six times as long as wide, 

 and in contact for only a small fraction of their length. Apertural margins 

 normal, straight, occupying fully two thirds the width of the stipe. 

 Description. — The stipes have a slight concave curvatiu-e, and are of uniform 

 width throughout their length. 



The first theca (th. 1^) originates close to the apex of the sicida, and 

 grows downwards closely appressed to it throughout its length, curving away 

 only when the aperture is reached. The second theca (th. l") is continued 

 from the crossing canal close to the aperture on the other side of the 

 sicula, so that there is a marked want of symmetry as regards the origin 

 of the branches. The sicula is 2-1 mm. in length, and the theca? have a similar 



length. 



Affiuifirs. — The angle of inclination is rather 



Figs. '20« and 6.— D«?v/)/(oiyra|'<M.s, cf. " • m m » i i . i <• 



jiliformis, Tuhbeig. lower than lu iullbergs type, but the form agrees 



closely with D. filiformis in other particulars. It 



does not seem to l)e closely allied to any other 



species, but is characterised by its general shape, 



y* uniformly slender width, want of symmetry at the 



' proximal end, and the remoteness of the thecje. 



It is pro^^sionally placed in this group on account of 



** its general form. In the characters of its proximal 



a. Sj)ecimeu in relief, natural size. , , . . i i n- n ^ 



BennaneHead,Bailantrae. Coll. end, howcver, it IS more clossly allied to the group 



Lap worth. i- r) „„,7 , „^, 



b The same, obverse view, x 5. "^ ^- '^•^f'?^''5^«^'- 



Horizon and Localities. — It has been found by 

 Jiapworth and the officers of H.M. Geological Survey in the Arenig rocks of 

 Bennane Head, near Ballantrae. 



