232 Dr. H. A. Nicholson on neio Species of GraiHoIites. 



familiar B. Gei'mfzi'anns, Barr. ; and it seems safest at present 

 to restrict the genus entirely to this species. Retiolites venosus, 

 Hall, and B. perlatus, Nich., possess a solid axis, and are 

 likewise distinguished by an extraordinary structure of inter- 

 lacing reticulated threads, the exact nature of which has yet 

 to be discovered. These will probably have to be placed in a 

 genus by themselves. There remains B. ensiformis, Hall, 

 wliicli occurs in the Quebec group of Canada, and which Hall 

 himself hints should probably be removed from BetioUtes. 

 This last form agrees with the characters of Trigonograjpsus 

 in having a well-marked solid axis from which the cell-parti- 

 tions alternately take their origin, in possessing perfectly plain 

 lateral margins, and in the general shape of the frond ; and as 

 their geological position is the same, there can be little hesita- 

 tion about placing the two in the same genus. 



Trigonograpsus laiiceolatus, Nicli. PI. XI. fig. 6. 



Spec. char. Frond flattened, obtusely pointed at the base, 

 and widening out with great rapidity, the breadth just above 

 the base being more than doubled in the space of half an inch. 

 The lateral margins of the frond are bounded by an elevated 

 line, and are perfectly plain, the cellules being in contact 

 throughout their entire length, so that the cell-mouths are all 

 in a line. Along the centre of the frond runs a strong, zigzag, 

 solid axis, from the opposite angles of which there arise in an 

 alternating manner strong cell-partitions, Avhich run nearly to 

 the margin, and form with the axis as high an angle as 75°. 

 The test shows no traces of a punctated or reticulated struc- 

 ture. 



This form is certainly in many respects allied to Trigono- 

 grapsus {BetioUtes) ensiformis, Hall ; but it is separated by 

 very well-marked characters, of which the more important are 

 the nearly straight axis in the latter, and the much greater 

 obliquity of the cellules, which form with the axis an angle of 

 not more than 50°. In our species, on the other hand, the 

 axis is strongly bent from side to side, and the cellules form 

 with it an angle of about 75°. 



Loc. Upper beds of the Skiddaw Slates, Ellergill, near 

 Milbiirn. 



Dichograpsus fragilisj Nich. PI. XI. figs. 1-3. 



Sjjec. char. Frond multibrachiate, consisting of several 

 (probably eight) simple, monoprionidian stipes, arising from a 

 median non-celluliferous funicle. Centrally is placed a small 

 pointed radicle, from which proceed the two primary divisions 

 of the funicle. These subdivide, at a distance of about half a 



