DICELLOGRAPTUS. 141 



horizontal direction, giving off a long spine below the aperture, which seems to 



open in a direction parallel with the general direc- 



Figs. 85 a and b.— Dicellograptus com- . . 



planatus, var. ornatus, nov. tioil of growth of the rest of the stipe. Ill SOI11C 



specimens these two primary thecas appear to have 

 been entirely modified to stout spines which have 

 a length of 4 — 4'5 mm. Th. 2 1 and th. 2 2 are of 

 unusual length, measuring commonly 1*7 — 2 mm. 

 long. They grow right back to the sicula, but we 

 have been unable to determine exactly how they 

 arise. No theca subsequently developed measures 

 more than 1*4 mm. 



Affinities. — Var. ornatus may be readily distin- 

 guished from all other Dicellograpti by the abnormal 

 size of its lateral spines. 



Horizon and Localities. — Upper Hartfell Shales. 



a. Proximal end, showing large -l.it- . 



eral" spines. Enlargement of part (ZiOUe Ot JJlCCl h)ij . anceps). 



6. Compi.'.tr sp.-dmen' showing charac- S. Scotland. — Dobb's Linn. 



ters of thec.i'. Dubb's Linn, Hart- i • , , ir , 



ieii shahs. Coll. Wood. Associates, etc. — Var. ornatus occurs on a some- 



what higher horizon than Dicellog. complanatus itself, 

 being found in some abundance in the zone of Dicellog. anceps, where it is 

 associated with the zone fossil and numerous Diplograpti. 



The best specimens at present known are in the Authors' collections and in that 

 of the Sedgwick Museum, those in the latter having been collected and presented by 

 Mr. William Swanston of Belfast. 



Dicellograptus anceps, Nicholson. Plate XX, figs, o a — e. 



1867. Dldymoyrapsus anceps, Nicholson, Geol. Mag., vol. iv, 1867, ]>. 110, pi. vii, figs. 18 — 20. 



1870. Dldymoyrapsus anceps, Nicholson, Ann. Mag. Nat. Hist. [4], vol. v, p. 351, pi. vii, fig. 5. 



1871. Dicellograpsue anceps, Hopkiuson, Geol. Mag., vol. viii, p. 335, pi. i, fig. 5. 



1876. Dicellograptus anceps, Lapworth, Cat. West Scott. Foss., pi. iv, fig. 82. 



1877. Dicellograptus anceps, Lapworth, Grrapt. of Co. Down, pi. vii, fig. 5. 



1890. Dicellograptus anceps, Tornquist, Undersdk. ofver Siljansomr&dets Graph i, p. 2 L,pl.ii,figs.l6 —ID. 



Stipes 2 — G cm. in length, somewhat rigid proximally but slightly curved 

 distally, and having an average uniform width of 1 mm., diverging at an 

 angle of 340° from an inconspicuous sicula. Virgella short, lateral spines 

 often conspicuous. Thecae ten to eight in 10 mm., free outer wall approxi- 

 mately straight, overlapping one half to one third their length. Apertures 

 horizontal, situated in semicircular excavations occupying nearly half the 

 width of the stipe. 



Description. — Isolated fragments of stipes frequently attain a length of 5 — cm., 



