C LIMACOGRAPTUS. 207 



1852. Diplograpsus teretiusculus, Salter, Quart. Journ. Geol. Soc, vol. viii, pi. xxi, fig. 3 d. 



1875. Diplograptus dentatus, Hopkinson, Quart. Journ. Geol. Soc, vol. xxxi, pi. xxiv, fig. 5 a. 



1870. Climacograptus Scharcnbergi, Lapworth, Cat. West Scot. Foss., pi. ii, fig. 55. 



1877. Climacograptus Scharcnbergi, Lapworth, Proc. Belfast Nat. Field Club, p. 138, pi. vi, 



fig. 36. 

 1898. Climacograptus Scharcnbergi, Elles, Quart. Journ. Geol. Soc, vol. liv, p. 519. 



Polypary 1 to 4 cm. in length, widening almost at once to a maximum width of 

 about 1*5 mm., and maintaining this breadth almost to its distal extremity. 

 Sicula 0*5 mm. in length with robust virgella. Septal groove well-marked, 

 conspicuously zig-zag in form. Thecse fourteen to eleven in 10 mm., 

 markedly alternate, short, overlapping one-third to one-fourth their length, 

 and having their distal extremities very slightly introverted and introtorted; 

 apertural margins situated in wide and deep excavations occupying one- 

 fourth of the ventral margin of the polypary and about one-third of its 

 width. 

 Description. — The specimens vary greatly in length, but all have an average 

 width of 1*5 mm. The breadth at the proximal end is 0*6 mm., but the increase 

 takes place so rapidly that the maximum width is attained at a distance of 6 mm. 

 from the proximal end. 



In the obverse view of the polypary the sicula is 



Figs. 139 a to c — ciimacograptus only visible in part in mature specimens, its apical 



region being imbedded apparently as a result of the 



f growth of th. 2 2 across it in front; judging, how- 



ever, from young specimens, it must have measured 

 fully 1 mm. in length. Th. I 1 appears to originate 

 5 mm. above the aperture of the sicula and grows 

 downward to the level of the aperture, then bending 

 round abruptly, grows upward and outward ; from 

 a b c it there is developed th. I 2 , which in its initial region 



a. obverse view, showing sicula. Dobb's crosses the sicula obliquely, leaving it free for a 

 of ct' TTOsoni) ar coii Wood* e short distance on the right side. Th. 2 1 is developed 

 b - ^ ^oTand tnj v^eS from th. l\ and from th. 2 1 two thee* grow, namely 

 .p Ibld - . ... th. 2 2 and th. o 1 : at this point the septum makes its 



c. Eeverse view, specimen showing very 1 1 



stout rod-like virgella. ibid. appearance, but in the obverse aspect it is seen 



earlier. 



In the reverse view of the polypary the mode of origin of the thecge is clearly 

 seen, and in some specimens the base of the sicula is visible, but in others it is 

 obscured by the stout virgella, which may exceed 1 mm. in length. 



The septal groove is distinctly angulated, running in short zig-zags from side 

 to side. From the outer part of each angulation proceeds a short horizontal 

 groove continuous with that of the septal groove itself. 



