MONOGRAPTUS. 



453 



Affinities. — In the general form of the polypary and characters of the thecas 

 Monog. BecH shows some approximation to M. retroflexus, but the initial region is 

 far more slender and thread-like. It also bears a certain amount of resemblance to 

 M. dextiwsus, but differs in its more slender proximal termination, and to some 

 extent also in the characters of the thecae. 



Horizon and Localities. — Gala-Tarannon Beds (zones of M. turriculatus and M. 

 crlspus). 



S. Scotland: Meigle Quarry ; Caddonfoot; etc. Ireland: Portaferry, Co. Down. 

 Wales: River Twymyn, Llanbrynmair. 



Associates, etc.— Monog. Beclci seems to be rather a rare fossil in the /one of 

 M. crispiis, where it occurs associated with M. crixpus, M. exiguus, M. mains, M. 

 cjalaensis and M. Marti. It is also found, but less commonly, in the zone of M. 

 turriculatus. 



Collections. — Belfast Natural History Museum, Swanston, Sedgwick Museum, 

 Lap worth, and the Authors. 



Monograptus exiguus (Nicholson). Plate XL VI, figs. 1 a — (/. 



1868. G raptotites Ubiferus var. exiguus, Nicholson, Quart. Journ. Geol. Soc, vol. xxiv, p. 533, pi. xix, 



figs. 27, 28. 

 1871. Ghrarptoliikus plumosus, Baily, Mem. Geol. Survey, Ireland, Sheet 49, 50, p. 23, figs. 1 a, b, c. 

 1876. Monograptus exiguus, Lapworth, Geol. Mag. [2], vol. iii, p. 503, pi. xx, fig. 6. 

 1892. Monograptus exiguus, Tornquist, Siljansomracl. Grapt., ii, p. 25, pi. ii, fig. 22. 



Figs. 312 <i — <•. — Monograptus exiguus 

 (Nicholson). 



Polypary short, slender, arcuate, fish-hook like, with double curvature at the 

 proximal end, and of approximately uniform breadth throughout, not 



exceedino- *5 mm. Thecae on the concave 

 margin, fourteen to twelve in 10 mm., small, 

 of the general type of M. lobiferus, but with 

 practically the entire apertural region coiled 

 up into a dense lobe, occupying one-half of 

 the total breadth of the polypary ; overlap 

 insignificant. 

 Description. — The form of the polypary recalls 

 that of M. Xilssoni, only on a smaller scale, the 

 polypary rarely exceeding 3 cm. in length ; the thecae 

 are on the concave margin except at the proximal 

 end, where the curvature changes and the thecae are 

 for a short distance on the convex side. At the 

 extreme proximal end the width of the polypary is 

 about "25 mm., but it widens rapidly to a maximum 

 of *5 mm., which is then maintained. 



a. Proximal fragment, showing sicula, 

 but with thecffi poorly preserved. 

 Portaferry, co. Down; Tarannon 

 Beds. C. 11. Swanston, Belfast. 



h. Distal thecae in low relief. Enlarge- 

 ment of part of PI. XLVI, fig. 1 d. 



< . Distal thecae, in full relief, showing 

 the coiled lobes. Bont Green, River 

 Twymyn, Llanbrynmair; Brynniair 

 Beds. Coll. Wood. 



