PETALOGRAPTUS. 



277 



Fig. 190. — Petalograptus palmeus, var. 

 tenuis, Barr. 



(2) in the smaller number of thecas in the same unit of length ; (3) in the relative 

 proportions of the thecas and in the general absence of curvature of their walls. 

 The polypary is usually small, but may be as much as 1*3 cm. in length ; it has 



an average uniform breadth of 1*5 mm. The thecas 

 number twelve in 10 mm., and are relatively shorter 

 than in other forms. They are about 1 mm. in 

 length, twice as long as broad, and overlap one half 

 their length. The earlier thecas have slightly curved 

 walls, but those subsequently developed are practi- 

 cally straight. The angle of inclination is uniformly 

 about 35°, and the apertural margins are concave 

 and oblique. 



A septum is present, but apparently is only 

 partial. The virgula may be distally prolonged. The 

 sicula is somewhat smaller than in the typical form. 

 Horizon and Localities. — Upper Birkhill and Lower Gala. 



S.Scotland: Dobb'sLinn; BelcraigBurn. Lake District : Skelgill ; Pull Beck. 

 Wales : Conway ; Llanystwmdwy, near Criccieth ; R. Twymyn, Llaubrynmair ; 

 Tarannon River, etc. 



Associates, etc. — Var. tenuis has much the same range as the typical form ; 

 it extends from the top of the zone of Monog. gregarius to that of the zone of 

 M. turricidatus at the base of the Gala beds. It is never a very common fossil. 

 In general it is found associated with Monog. convolutus and M. gregarius, in the 

 Birkhill Shales ; and with M. turricidatus, M. exiguus, M. runcinatus and M.jpandus 

 in the Gala-Tarannon beds. 



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



Complete specimen, showing sicula and 

 well-marked growth-lines, obverse 

 aspect. Enlargement of PI: XXXII, 

 fisr. 3 c. 



Var. ovato-elongatus, Kurck. Plate XXXII, figs. 4 a. — d. 



1850. Graptolithus palmeus, Barrande, Grapt. de Bohcme, pi. iii, fig. 7. 



1851. Petalolithus palmeus, Suess, Ueber Bohmische Graptolithen, pi. viii, fig. 1. 



1868. Diplograptus palmeus, Nicholson, Quart. Journ. Geol. Soc, vol. xxiv, p. 523, and pi. xix, figs. 



2,3. 

 1876. Diplograptus palmeus, Lapworth, Cat. West. Scott. Foss., pi. i, fig. 27. 

 1881. OepTialograptus ovato-elongatus, Kurck, Nagra Nva Graptolitarter fran Skane, Geol. Foren. 



Forhandl., vol. vi, p. 303, pi. xiv, fig. 10. 

 1890. Diplograptus ovato-elongatus, Geinitz, Graptoliten des k. miueralog. Mus. Dresden, pi. a, 



fig. 40. 

 1897. Petalograptus palmeus var. ovato-elongatus, Elles, Quart. Journ. Geol. Soc, vol. liii, p. 197, 



pi. xiv, figs. 11-14. 



A third variety, var. ovato-elongatus, may in its mature form be very readily 



