PETALOGRAPTUS. 



281 



S. Scotland : Dobb's Linn (Long Cliff) ; Garple Linn ; etc. Lake District : 

 Skelgill. Wales: Rhayader; Twymyn Valley, Llanbrynmair ; Afon Fadre, 

 Pennant ; Pary's Mountain, Anglesea. 



Associates, etc. — P. minor is not an uncommon form in the zone of Monog. 

 gregarius, but it is most abundant in that part corresponding with Marr and 

 Nicholson's zone of M. fimbria tus, where it is found associated with M. gregarius 

 and M. fimbriatus. 



Collections. — Sedgwick Museum, Marr, and the Authors. 



Petalograptus altissimus, sp. nov. Plate XXXII, figs. 7 a — e. 



Pigs. 194 a — c. — Petalograptxis altissimus, 

 sp. nov. 



Polypary large, massive and thick, having a length 2 — 3 cm. and a maximum 



breadth of 4 mm. when compressed. Sicula long, septum incomplete. 



Thecae ten in 10 mm., alternate, long tubes of the usual Petalograptus type, 



three times as long as wide, overlapping fully three quarters of their 



length ; apertural margins slightly concave, everted. 



Description. — The polypary is unusually robust, and, like that of all the 



Petalograpti, its breadth, which is attained by gradual widening, is great relative 



to its length ; there is usually a slight diminution in width in the distal region. 



The sicula is long and thin ; in the obverse aspect it is seen to have a length of 

 fully 2 mm. ; th. I 1 originates from above the aperture of the sicula, and grows 



outward and upward, while th. V 2 develops 

 from the latter in such a way as to conceal 

 the whole structure in the initial part of the 

 polypary in the reverse aspect, and give it 

 the protracted Petalograptid character. The 

 aperture of th. 2 3 reaches to the level of 

 the apex of the sicula, where the septum 

 commences. 



A transverse section of the polypary 



shows that the septum is very insignificant, 



'kr extending inwards but a short distance from 



the obverse side. In the reverse aspect no 

 trace of a septum is seen, but the alternate 

 growth of the thecae is often very beauti- 

 fully shown. 



The thecae are long, narrow tubes, with 

 curved walls, which are in contact for almost 

 their whole length, and their flattened concave apertures are markedly oblique. 

 Affinities. — P. altissimus may be said to resemble all the other Petalograpti in 



37 



^ 



a. Obverse aspect, showing sicula ; in full relief. 



Llanystwmdwy, near Criccieth. Tarannon 

 Beds (zone of M. turriculatus). Coll. Fearn- 

 sides. 



b. Distal thecse, part preserved in relief, part as 



a cast ; note partial septum. Ibid. 



c. Distal thecae, preserved as a cast ; note absence 



of septum in reverse aspect. Ibid. 



