282 BRITISH GRAPTOLITES. 



its genera] features ; it is, however, distinguished from all forms hitherto described, 

 by its larger size and greater thickness. From Mesog. magnus, to which it has 

 some superficial resemblance, it may be separated readily on account of the totally 

 different character of the thecse of the proximal end. 



Horizon and Localities. — Upper Birkhill Shales (zone of Bastrites maximus) ; 

 Gala-Tarannon (zone of Monog. turriculatus). 



S. Scotland : Dobb's Linn ; Belcraig, etc. Wales-: Llanystwmdwy ; Pontbren- 

 dibyn, Llanbrynmair ; two hundred yards south of Parbryn Sands, Cardiganshire. 



Associates, etc. — P. altissimus occurs in some abundance in the above-mentioned 

 zones in S. Scotland and "Wales; it is commonly associated with Bastrites maximus 

 and Monog. turriculatus. It is frequently preserved in relief. 



Collections. — Lapworth, 0. T. Jones, Fearnsides, and the Authors. 



Petalograptus folium (Hisinger). Plate XXXII, figs. 8 a — e. 



1837. Prionotns folium, Hisinger, Lethaea Suecica, Suppl., p. 114, pi. xxxv, fig. 8. 



1843. Prionotus folium, Portlock, Geol. Eep. Londonderry, p. 321, pi. xx, fig. 5. 



1880. Diploijraptusfolium, Tornquist, Geol. Fiiren. Forhandl., vol. v, p. 442, pi. xvii, fig. 7. 



1882. Cephalograptus folium, Tullberg, Bihang till k. Svenska Vet.-Akad. Hand], vol. vi, no. 13, 



p. 15, pi. i, figs. 15—19. 

 1890. Diplographis folium, Geinitz, Graptolithen des k. mineralog. Mus. Dresden, p. 26, pi. a, 



figs. 44 — 46. 

 1897. Petalograptus folium, Elles, Quart. Journ. Geol. Soc, vol. liii, p. 188, pi. xiii, figs. 1 — 5. 

 1897. Diplograptus folium, Tornquist, Diplogr. and Heteroprionidae of Scanian Bastrites Beds, 



Acta Beg. Soc. Physiog. Lund., vol. viii, p. 12, pi. ii, figs. 1—4. 



Polypary 1*5 — 2 - 5 cm. in length, narrow proximally but widening quickly to 



a breadth of G mm. opposite the apertures of the fourth pair of thecas, and 



maintaining this width to the distal extremity, or continuing to widen 



almost imperceptibly up to 7 mm. Thecas ten in 10 mm., inclined 5° — 20°, 



about 7 mm. in length, six times as long as wide, overlapping two thirds 



or more ; apertural margins concave, oblique, except at distal extremity, 



where they are horizontal. 



Description. — The sicula has a length of about 2 mm. ; it usually shows a 



virgella, and is generally visible for its entire length in the obverse aspect of 



the polypary ; it is free for a fraction of its length on the right side. In the 



reverse aspect, only the base of the sicula and a very small portion of its side are 



visible, the rest being concealed by the initial part of the second and subsequent 



thecas. Th. I 1 originates a little way above the aperture of the sicula, and grows 



downward to a point slightly below it, then turning, grows slightly outward and 



upward. It is usually rather more than three times as long as the sicula, and 



attains a length of 7 mm. 



