CEPHALOGRAPTUS. 289 



Cephalograptus (?) acuminatus (Nicholson). Plate XXXII, figs. 11 a — d. 



1867. Diplograptus acuminatus, Nicholson, Geol. Mag., vol. iv, p. 109, pi. vii, figs. 16, 17. 

 1897. Diplograptus acuminatus, Tovnquist, Acta Reg. Soc. Physiog. Lund., vol. viii, p. 14, pi. ii, 

 figs. 5—7. 



Polypary 1- — 3 cm. in length, straight or slightly curved, increasing gradually 



from a narrow protracted proximal extremity to a maximum breadth of 



1*5 mm., which is maintained up to the distal extremity. Sicnla very long 



and slender. Thecas approximating to the Glyptogra/ptus type, about ten in 



10 mm., long narrow tubes with an average length of 2 — 2*5 mm., inclined 



at 20° ; outer walls with sigmoid cnrvatnre, overlapping one half their length ; 



apertural margins introverted, with acute denticle when compressed. 



Description. — The proximal end is protracted, the maximum width of the 



polypary being attained about 1 cm. from the proximal extremity. The sicula has 



a length of 2*5 mm. and is very slender ; it is usually free for almost its entire 



length on one side in both aspects of the polypary, 



Fig. 109. — Ccphaloqraptus (?) acumin- ,i • i , i n .i , • i i i i 



atus (Nicholson). the extreme apical part being all that is embedded. 



The virgella is short, never exceeding 1 mm. in 

 length, and is only rarely preserved. The virgula 

 is sometimes seen to be distally prolonged. 



Th. I 1 originates from a point about 1 mm. above 

 the aperture of the sicula, and grows almost straight 

 upward at once, attaining a length of 2 mm. or more ; 

 th. I 2 buds from th. I 1 at about the level of the apex 

 of the sicula, and, growing straight outward and 

 upward, attains a length slightly less than that of 

 th. r. 



The thecal apertures are introverted, with an 

 acute denticle when compressed ; but in specimens 

 n , . • ■ preserved in relief the apertures are nearly straight 



Complete young specimen, obverse 1 1 J o 



aspect. DoWs Linn, Lower Birk- an( J not gQ obviously acuminate. GrOWtll-lineS 



hill Shales. Coll. Sedgwick Museum. ^ 



parallel to the apertures may occasionally be 

 detected, and a complete septum always appears to be present. 



Affinities. — The systematic place of Ccplialog. (?) acuminatus is uncertain. In 

 the general characters of the theca3 it certainly differs from any other Cephalograptus 

 or Petalograptus as yet described, and comes nearer the Glyptograpti ; while, as 

 regards the character of the proximal end it clearly approaches the Dimorphograjiti, 

 though it is still a Diplograptid. 



We place it provisionally with the Cephalograpti on account of its resembling 



88 



