510 



BRITISH GRAPTOLITES. 



sixth tlieca, though it has been known also from the fifth ; but in the specimens 

 from the Lake District it usually arises from the seventh and more rarely from 

 the eighth. 



The sicula is usually conspicuous, measuring fully 1 mm. in length. 



Affinities. — The only Cyrtograptns with which Gijrtog. si/mmetr'icus is likely to be 

 confused is G. rigiJus, and from this it differs (1) in having a much shorter and 

 robuster proximal portion, with a more conspicuous sicula, (2) in the abrupt 

 widening and general breadth of the adult portion as compared with the proximal 

 portion of the polypary, and (o) in the number of thecse in the same unit of 

 length. 



Horizon and Localities. — Wenlock Shales (zone of Cyrtog. si/mmetricus). 



Welsh Border : Builth Road ; Castle Crab, near Builth Road ; Coed Mawr, 

 near Builth Road. Lake District : Cautley. 



Associates, etc. — Cyrtog. symmetricus is associated with Monog. dubius and M. 

 capiUacens. 



Collections. — Marr, Welch and Watney, Mr. F. A. Marr, and Elles. 



Cyrtograptus hamatus (Baily). Plate LII, fig. 3. 



1861. Grapiolithus hamatus, Baily, Grapt. Co. Meath, Journ. Geol. Soc. Dublin, vol. ix, p. 305, 

 pi. iv, figs. 6 A and b. 



Fig. 356. — Cyrtograptus hamatus 

 (Baily). 



Proximal portion, showing sicula, tliecce 

 of stipe, and cladium. Enlargement 

 of part of PI. LII, fig. 3. 



Polypary small, stipe strongly recurved in the 

 proximal portion and possessing one cladium 

 only. Thecae eight to six in 10 mm., sub- 

 triangular, with reflexed apertural margins 

 in the proximal portion, but becoming more 

 tubular distally Avitli overlap one-third to 

 one-half their length both on the main stipe 

 and on the cladium. 

 Description. — The polypary is small, the diameter 

 of the proximal arc not exceeding 8 mm. 



The sicula is conspicuous, measuring 1*5 mm. in 

 length, and is furnished with a short but stout vir- 

 gella; tli. 1 originates about half way along its length. 

 There are eleven thecse of the ordinary sub- 

 triangular type and the cladium is developed at the 

 tenth ; the thecaB then become more distant and show 

 distinct sigmoid curvature of their walls, and both 

 on stipe and cladium they have even and horizontal 

 apertures. 



