320 C. Lajyioorth — On Scottish Monograptidce. 



Portlock's original figure of Lis Graptolites tenuis is certainly very 

 indifferent, but there can be no question that it was intended for the 

 species we are describing. The Graptolitic schists of Limehill, 

 whence his examples were procured, are in certain localities crowded 

 wath this form ; and no other Sjoecies of the Nilssoni group seems to 

 occur there. The figures given on Plate XL (Figs. 3 I, m, n) are from 

 specimens collected from these beds by mj^self. The Irish examples 

 show all the peculiarities of the species as given above — the 

 characteristic dorsal curvature of the 'polypavj, the approximate and 

 obscure or prolonged denticles of the distal portion, and the distant, 

 pointed or reverted denticles near the proximal extremity. 



Many of the same features seem to be characteristic of the form 

 Graptolites discretus of Professor Nicholson; which is probably 

 identical with the present species. 



Locality. — Monograptus tenuis is perhaps the commonest fossil of 

 the Birkhill Shales, occurring everywhere in great abundance, as at 

 Ettrickbridgend, Dobbs Linn, Frenchland, Belcraig, etc. It occurs 

 also but very rarely in the succeeding Gala Group at Darnick 

 Bridge, Eddleston Waterhead, Overshiels, etc. 



12. MoNOGRAPTUS Sandersoni, sp. nov. Plate XL Figs. 2 a — e. 

 Polypary of great length, distal portion slightly arcuate, and having 



a maximum diameter of one-thirtieth of an inch, proximal portion 

 long, filiform and sharply incurved. HydrothecEe M to 18 to the 

 inch, adpressed to the concave margin of the periderm, in contact 

 only ; long and narrow, with inclined apertural margin and an acute 

 but inconspicuous denticle. 



Commencing with an extremely slender flagelliform portion, the 

 polypary augments its diameter very slowly, so that nearly a foot of 

 length is attained before the point of maximum width is reached. 

 The adult organism must have possessed a length of more than 

 eighteen inches. The hydrothecae, which are less than one-fiftieth 

 of an inch in average diameter, are somewhat sacculate near their 

 distal end, but for the greater portion of its length the exterior 

 edge of each is quite straight. The margin of the aperture is 

 invariably inclined. The denticle, though remarkably acute, is 

 never so prominent as in Mono, tenuis or Monogr. Nilssoni. 



Straight fragments from the neighbourhood of the proximal 

 extremity may sometimes be confounded with Mono, attenuatus, 

 Hopkinson. The long slender polypary and narrow peculiarly 

 shaped hydrothecse at once distinguish it from all other forms. 



I dedicate this species to my friend W. A. Sanderson, Esq., of 

 Galashiels, without whose generous assistance the complete descrip- 

 tion of many of these forms would have been practically impossible. 



Locality. — Birkhill Shales, Middle zones ; at Dobbs Linn, French- 

 land, Belcraig. 



13. MoNOGRAPTUs coNCiNNUs, sp. nov. Plate XL Figs. 1 a—e. 

 Polypary curved, of great length ; gradually enlarging through a 



very narrow incurved proximal portion to a maximum diameter of 

 one-sixteenth of an inch. Hydrothecse 20 to 24 to the inch, adnate 



