18G8.] NicnoLsox — coniston-flag graptolites. 527 



DiPLOGRAPsus PFTiLLus, Hall, sp. PI. XIX. figs. 17, 18. 



GraptolWius putillus, Hall, Grapt. Quebec Group, p. 44, pi. A. 

 figs. 10-12. 



Frond diprionidian, about ^ inch in length and 1 line in 

 breadth. Base apparently pointed. The frond forms a cylin- 

 drical tube, divided into two vertical compartments by a longi- 

 tudinal septum, the lateral edges of which appear on the exterior of 

 the test as two gently undulating lines between the rows of cellules. 

 The common canal is, comparatively speaking, very wide. The 

 cellules are about 25 in the space of an inch, very narrow, curved, 

 with the convexities directed outwards, forming an angle of 10°, or 

 thereabouts, with the axis, and free for almost their entire length. 

 The ceU-mouths are rectangular to the direction of the cellules, or 

 rather more than rectangular to the axis. 



This exceedingly distinct species was described by Hall from the 

 Hudson-Uiver group of Iowa, and I have now found two specimens, 

 the first discovered in Britain, in the Coniston Flags of Westmore- 

 land. It is at once recognized by the breadth of the common canal, 

 and by the narrow, curved, nearly vertical cellules, which hardly 

 overlap one another at all, and possess cell-mouths which are more 

 than rectangular to the axis. 



Loc. Coniston Flags of Skelgill Beck, near Ambleside, beautifully 

 preserved in relief. 



DiPLOGRAPSUS VESICULOSUS, Mch. 



I have obtained a single fragment of this truly extraordinary 

 species, from the Coniston Flags of Skelgill Beck. Its characters, 

 however, are so anomalous that I shall reserve all description of it 

 for a future occasion, as it would occupy too much space in the pre- 

 sent paper. I merely mention it here to point out that it does not 

 possess a single character in common with D. pristis, His., of which 

 it has been asserted to be merely a variety. (See Carruthers, Geol. 

 Mag. vol. V. p. 130.) 



DiPLOGRAPSUS PRISTIS, His. 



Prionotus jpristis, Hisinger, Leth. Suecica, t. 35. fig. 5. 

 Dijplograpsus minutus (vel minimus), Carruthers, Geol. Mag. 

 vol. V. pi. 5. fig. 12, 



Frond diprionidian, varying in length from a quarter of an 

 inch to nearly 3 inches, exclusive of the distal prolongation of 

 the axis, which often adds another inch to the total length. The 

 breadth in the fully developed portion varies from ^ to ^ of an inch. 

 The general shape of the frond is extremely characteristic, being nar- 

 row at the base, and widening out gradually and regularly until the 

 full width is attained. This point may be reached in the lower third, 

 in the centre, or not till towards the distal extremity ; and when it 

 has been once attained, the frond either contracts slightly or con- 

 tinues of the same breadth to the end. The proximal extremity or 

 base is small and rounded, and is furnished with three radicular pro- 



VOL. XXTV, PART I. 2 



