CYRTOGRAPTUS. 



509 



f 



with wliicli specimens are broken about midway between tlie sicula and the 



cladium, it is possible that the Avhole did not lie 

 FiGs.354:aandh.—Cyrtograptusrigidus, exactlv in one and the Same plane. 



Tullbers:. -^ _ . 



The sicula measures '5 mm. in length. 

 Affinities. — In the possession of only one cladium, 

 as in general characteristics, Giji'tog. rigidus ap- 

 proaches G. symnietricus. It is, however, a larger 

 and more gracefully curved species ; there are far 

 more thecse in the proximal portion before the 

 cladium is given ofP, and the whole proximal end is 

 very much more attenuated. 



Horizon and Localities. — Wenlock Shales (zone 

 of Ci/rtog. rigidus). 



Welsh Border : Dulas Brook, near Builth ; River 

 Irfon, near Builth. Montgomeryshire ; Sale Quarry, 

 near Middleton Station. 

 Associates, etc. — Gijrtog. rigidus occurs associated with Monog. retroflexus, M. 

 dubius and M. Flemingi, var. yrimus. 

 Collection. — Elles. 



a. Part of stipe and cladium, showing 

 form of proximal thecae. Enlarge- 

 ment of part of PI. LII, tig. 2 h. 



h. Distal thecae of the cladium. En- 

 largement of part of PI. LII, fig. 2 c. 



Fig. 355. — Cyrtograptus symmetricus, 

 Elles. 



Cyrtograptus symmetricus, Elles. Plate LI, figs. 5 a — c. 



1900. Cyrtograptus symmetricus, Elles, Quart. Journ. Geol. Soc, vol.lvi, p. 410, pi. xxiv, figs. 4 a, 4 b. 



Polypary relatively small, stipe with short stiffly recurved proximal portion, 

 widening rapidly from the initial portion till the maximum of 1'5 mm. is 



attained ; bearing one cladium only agreeing 

 in all particulars with the termination of the 

 main stipe. Tliecas twelve to nine in 10 mm. 

 those of the proximal portion sub-triangular 

 with reflexed apertural margins and in con- 

 tact only, but becoming quickly more tubular, 

 and overlapping fully one-third to one-half 

 their length in the distal portion. 

 Description. — The polypary is somewhat stiff 

 looking, though both stipe and cladium may show 

 slight curvature ; the proximal portion is slender 

 compared with the distal portion. 



There are usuallv not more than eight thecse of 



the proximal type, and the cladium seems to vary 



somewhat in its position ; it usually arises from the sixth, seventh or eighth theca. 



In specimens from the Welsh Borderland the cladium commonly arises from the 





.^^^ 



Proximal portion, showing sicula, theese 

 of the stipe, " saccoid," and part of 

 cladium. Castle Crab, near Builth ; 

 Wenlock Shales. Coll. Elles. 



