MONOGRAPTUS. 



109 



Associates, etc. — Monog, convolutus is a fairly common fossil, though often only 

 in a fragmentary condition, in the zone to which its name has been applied, where 

 it occurs associated with M. limatulus, M. involutus, M. Clingani, M. lobiferus, M. 

 leptotheca, Bastrites peregrinus, Climacog. scalaris, Gephalog. cometa, etc. 



Collections. — Geological Survey of England and Wales, and of Scotland, 

 British Museum (Natural History), Sedgwick Museum, Lapworth, and the 

 Authors. 



Figs. 325 a — c. — Monograptus decipiens, Tornquist. 



Monograptus decipiens, Tornquist. Plate XLVIT, figs. 3 a — e. 



1899. Monograptus decipiens, Tornquist, Monog. of Scaniau Bastrites beds, p. 20, pi. iv, figs. 9 — 14. 



Polypary small, in the form of a rather irregular plane spiral, widening rapidly 

 from an initial breadth of 1 mm. to a maximum diameter of about 2 mm. 

 Thecee ten to eight in 10 mm., on the convex margin ; of two types, those 

 of the proximal portion of the linear isolated Bastrites type, those of the 

 distal portion in contact, triangular, free about seven-ninths of their length, 

 with relatively conspicuous apertural barbs, in which about one-third of 

 this free portion is involved. 

 Description.. — The polypary varies somewhat in form, but consists generally 



of two involutions, and the distal extremity 

 tends to become straight. In its proximal 

 portion it augments very rapidly in width, 

 and the change from the isolate thecas of 

 the initial region to the broader triangulate 

 theca?, which increase very rapidly in size 

 throughout the early whorls, is most 

 striking and characteristic. 



The sicula is rather short, not reaching 

 the isolate region of th. 1. 



The thecas as a whole change their form 

 gradually, those of the distal portion of the 

 polypary having more conspicuous aper- 

 tural barbs than is usual in most members 

 of this group. 



Affinities. — Monog. decipiens approaches M. convolutus in respect of its general 

 shape, but differs in the more rapid augmentation in width in the proximal portion 

 and also in the characters of the distal thecas, which have far more conspicuous 

 apertural barbs. From M. involutus, which it also somewhat resembles, it is distin- 

 guished by these same characters and by the presence of Rastrites-like thecas in 

 the initial portion of the polypary. 



a. Proximal fragment, showing sicula. E. side 

 Quarry, N.E. of Fagwr-fawr Farm, Pont Erwyd, 

 Cardiganshire. Geol. Survey of England and 

 Wales. 



h. Fragment in relief, showing characteristic barbs. 

 On same slab as PI. XL VII, fig. 3 c. 



e. Distal thecae. Enlargement of part of PI. XLVII, 

 fig. 3 d. 



