MONOGRAPTUS. 



395 



Wales : Llanfair, Montgomeryshire. 



Associates, etc. — It has been a Kttle difficult to determine the horizon of var. 

 Iii(lensis, but it is ahnost certainly a Lower Ludlow form ; M. dtihins is its only 

 associate. 



GoUections. — Geological Society of London ; Dr. Humphreys (Llanfair), Wood. 



Figs. 263 a—c. — Monn^raplus varians. 

 Wood. 



M 



1 



l-v > 



Monograptus varians, Wood. Plate XXXIX, figs. 6 a — e. 



1880. Monogra])tus colonvs, Lapwortli, Auu. Mag. Nal . Hist. [5], vol. v, p. 1-52, pi. iv, figs. 3 h — 3 d. 

 1900. Monograptus varians, Wood, Quart. Journ. Geol. Soc, p. 467, text-fig. 15, pi. xxv, figs. 14 a 

 and 14 b, 15, 16 A and 16 b. 



Polypary from 2 — 2'5 cm. in length, straight with slight ventral curvature 

 near the proximal end, width increasing throughout to a maximum breadth 



of about 2 mm. or rather less. Thecee 

 fourteen to ten in 10 mm., typically three at 

 the proximal end show retroverted apertural 

 extremities, those of maturer portion of the 

 polypary simple tubes with very wide aper- 

 tural margins, 2 mm. in length, from two 

 to three times as long as wide, overlapping 

 one-half their length, and with an average 

 inclination of 30° to 40°. Virgula con- 

 spicuous. 

 Descri^ption. — The polypary in Moiioy. varians is 

 always short, never apparently exceeding 2'5 cm. in 

 length and generally being only about 2 cm. ; the 

 increase in breadth takes place fairly rapidly in the 

 proximal portion, and thence is more gradually 

 continued right up to the distal extremity. The 

 virgula is generally very conspicuous at the distal 

 end of the polypary. 



The sicula has a length of about 2 mm. and is 

 long relatively to its breadth, reaching well above 

 the level of the second thecal aperture. 

 The ogee form of the proximal thecte is not nearly so conspicuous as in 

 M. colonus, though there are distinct traces of it in th. 1 ; all the earliest three 

 thecae may have retroverted apertural extremities, though this feature is some- 

 times not discernible in th. 3. In the thecee developed later the great width of the 

 apertural margin is often associated with a distinct compression of the ventral 

 wall of the theca next above, resulting in a most characteristic appearance. In 





b c 



a. Sicula and th. 1. Specimen on same 

 slab as PI. XXXIX, fig. 6 a. 



h. Proximal end. Figured, Quart. 

 Journ. Geol. Soc, vol. Ivi, p. 407, 

 fig. 1.5 6. Eoad above Garbett's 

 Hall, Long Mountain ; Lower Lud- 

 low Shales. Coll. Wood. 



c. Distal end, showing virgula and 

 character of thecae. Enlargement 

 of reverse side of jiart of PL 

 XXXIX, fig. 6 a. 



