MONOGRAPTUS. 



I II 



Fig. 303.— Monograptus tortilis 

 Linnarsson. 



■ 





' 



Enlargement of part of PI. XLIY, fig. 6. 



tendency to isolation though with a less conspicuous 

 and shorter hook. The overlap appeal's to vary 

 from one-half in the proximal portion of the poly 

 pary to one-third in its more distal portion. 



Affinities. — Monog. tortilis can readily be distin- 

 guished from all other members of the group by its 

 form and the characters of its thecse. 



Horizon and Localities.— Gala-Tarannon Beds. 



Lake Pis/rid : Sedbergh. 



Associates. — Monog. tortilis is a rare species in 

 Britain. It occurs associated with Mount/. Bechi, 

 M. niulns, and Petalog. palmeus. 



Collection. — Sedgwick Museum. 



IV. B. 1 : Monograpti in which the thecse are bi-form and the polypary approxi- 

 mately straight. 



Monograptus Sedgwickii (Port-lock). Plate XLIV, fig. 10 a—f. 



1843. Graptolithus (Prionotits) Sedgwickii, Portlock, Report Geol. of Londonderry, p. 318, pi. 



xix, fig. 1. 

 1850. Graptolites Sedgwickii, Harkness, Quart. Journ. Geol. Soc\, vol. vii, p. 60, pi. i, fig. 4. 

 1868. Graptolites Sedgwickii and var. spinigerus, Nicholson, Quart. Journ. Gteol. Soc, vol. xxiv, p. 



533, pi. xix, figs. 31, 32. 

 1876. Monograjdus Sedgwickii, Lapworth, Geol. Mag. [2], vol. iii, p. 357, pi. xiii, figs. 3 a — d. 

 1892. Monograptus Sedgwickii, Tornquist, Siljansomrad. Grapt., ii, p. 28, pi. ii, figs. 31 — 34; pi. 



iii, figs. 1 — 4. 



Polypary straight or slightly flexed, 20 cm. or more in length, widening 

 gradually from the proximal end to a maximum breadth of o mm. exclu- 

 sive of spines. Sicula relatively small. Thecas ten to six in 10 mm., with 

 slight ogee curvature and slight torsion ; apertural region alone isolate and 

 retroverted, occupying about one-half the breadth of the polypary. Aper- 

 tural margin spined, the spine becoming more conspicuous distally and the 

 amount of retroversion decreasing proportionately. Overlap slight. 

 Description. — The polypary must often have attained a great length, for distal, 

 fragments measuring 12 cm. or more are of frequent occurrence. These distal 

 fragments are commonly rigid and straight ; but Portlock's specimens from Ireland 

 — possibly his original types of the species, and at present preserved in the Jermyn 

 Street Museum — show an unusual amount of curvature throughout when compared 



