C. Lapworth — On Scottish Monograptidce. 357 



pary. It is placed here on the ground of its close relationship to the 

 typical form of M. Halli. 



Barrande figures several Bohemian examples in which the poly- 

 pary is more or less curved distally and has a circinate proximal 

 portion. This variety seems to be absent from our Scottish deposits ; 

 all our examples are straight and rigid. 



Locality. — Gala Group at Grieston, Tushielaw, Selkirk, Galashiels^ 

 etc. Girvan beds at Penwhapple. Eiccarton Beds at Kiccarton, 

 Mosspaul, Elliotsfield. Lower Pentland Beds at N. Esk Keservoir, 

 Habbies Howe, etc. 



§ VI. 



Group 4. — Type, Monogkaptus Sedgwickit, Portlock, sp. 



Polypary straight, or spirally enrolled. SJydrotJiecoi rising from the 

 convex edge of the periderm at a large angle ; subtrlangular in 

 form, with curvilinear margins and subterminal aperture. 



22. Monogkaptus Sedgwiokii, Portlock, sp. Plate XIII. Figs. 



Sa — d. 

 Graptolites Sedgivichii, Portlock ; Eep. Londonderry and Tyrone, 



plate xix. figs. 1, 2, 3. Harkness, Geol. Journ. vol. vii. plate i. 



figs. 4 a, h, G. Nicholson, var. spinigerus, Quart. Journ. Geol. 



Soc. vol. xxiv. plate xix. figs 31, 32. Monograpsus SedgwicTcii, 



Geinitz ; Die Graptolithen, Taf. 3, fig. 1. 

 Monograpsus Heuherni, Geinitz; Die Graptolithen, Taf. 3, fig. 11. 

 Polypary several inches in length, rigid, straight or with a slight 

 dorsal curvature, and having a maximum diameter of one-tenth of an 

 inch. Hydrothecse making an angle of about 60° with the line of 

 the virgula, 16 to 20 to the inch, subtriangular in form, rapidly 

 narrowing in the direction of the aperture, the margin of which is 

 convex, oblique, prolonged, and ornamented by a strong rigid hori- 

 zontal spine. 



The proximal portion of the polypary is straight, perpendicular, 

 and much wider than in any other form of the group. The sicula 

 is about one-tenth of an inch in length, and together with its attached 

 portion of the periderm is usually bent a little backwards. There is 

 no variation in the general shape of the hydrothec^ throughout the 

 whole of the extent of the polypary — those finally formed differing 

 from those near the sicula in size alone. The base of each, or that 

 portion which rests upon the common canal, is almost as broad as 

 the length of the theca. There is no overlap, the hydrothecae merely 

 touching each other at their bases. The outer margin of each is con- 

 cave and inclined at an angle which varies from 45° to 60°. The 

 distal margin is almost horizontal and more or less arched — the 

 outer portion forming the edge of the aperture. The denticle is 

 strongly mucronate, and is prolonged in a stout spine about one- 

 twentieth of an inch in length. In many examples this s^^ine seems 

 to be wholly wanting ; but the known facts go to prove that it is 

 universally present — its apparent absence depending either upon 

 the angle of compression or the state of preservation of the fossil. 

 By some palaeontologists this form is considered as identical with 



