CLIMACOdHAPTlfS. 



!»(»«.» 



L893. Glimacograptus inter nexus, Tornquist, Struct. Diprionidae, Ada Univ. Lund., vol. xxix, p. 6, 



figs. 23—27. 

 1897. Glimacograptus undulatus, Tornquist, Acta Reg. Soc. Physiogr. Lund., vol. viii, p. 9, pi. i, figs 



22 -24. 



Polypary - r > —10 nun. in length, having an average uniform breadth <>f rather 

 less than 1 mm. for the greater part of its length but narrowing slightly at 

 the proximal end, which is rounded off. Sicula visible for fully 0"5 nun. of 

 its length, situated obliquely, virgella short. Thecae sixteen to twelve in 

 10 nun., short tubes in contact for a small fraction of their length. Aper- 

 tural margins introverted and introtorted, situated in apertural excavations 

 occupying one-third the width of the ventral margin of the stipe and one- 

 third the total width. Septum always undulating. 

 Description. — Gl. Hughesi resembles closely a minute CI. Scharenbergi, and 

 owing to the degree of introversion and introtorsion of the thecae presents a very 



different appearance in the obverse and reverse 

 aspects, and perhaps this is the reason that two 

 species have been made out of this form. In the 

 obverse aspect the sicula is visible for fully 0'5 mm. 

 of its length, and is seen to be situated somewhat 

 obliquely within the polypary. Th. I 1 originates 

 midway along its visible length, and growing outward 

 and upward has its aperture on a level with the apex 

 of the sicula. 



In the reverse view the growth of the two 



earliest thecal entirely conceals the sicula except 



vcr.se view showing apical part of f or a sma ll fraction of the apertural region. The 



sicula. Enlargement of part of PI. A ° 



xxvn, fig. nb. thecal walls, while generally rectangular, show often 



c. Well-preserved specimen, obverse ... 



view, showing sicula and origin of a degree of sinuosity in their free outer part, but in 



th. I 1 . Twymyn Kiver, near Llan- 



Coll. the apertural region they seem to have undergone 





-( 'liiiKicuijiuiplns llttijh 

 (Nich.). 



1 v 



a. Small but typical specimen in relief. 



Ambleside Skelgill Beds. One of 

 Nicholson's original specimens. 

 Brit. Mus. (Nat. Hist.). 



b. Compressed specimen in relief, ob- 



brynmair, I>olgadfau Beds. 

 Wood. 



Climacograptus 



(Nich). 



Hughesi 



d. Distal tliecac, showing introversion 

 and introtorsion of the apertural 

 margins. Twymyn Kiver, I'enuant, 

 Dolgadfan Beds. Coll. Wood. 



some slight introtorsion, so that the apertures are 

 all directed towards the obverse side; this is only 

 noticeable in specimens preserved in relief. When 

 compressed the lower half of the apertural excava- 

 tion may appear perpendicular or slightly oblique. 

 Striae marking stages of growth can usually be 

 detected. There is a certain amount of variation in 

 breadth in different specimens, between 0'6 nun. and 

 1 mm., but individuals are of uniform width through- 

 out their whole extent. 



Affinities. — GL Hughesi resembles Gl extremus 

 in the undulating nature of its septal groove, but 



