2G0 BRITISH GRAPTOLITES. 



excavation, as such, disappears, and the line of the apertural margin, at first 

 horizontal, becomes decidedly oblique, and the form of the theca becomes 

 , , „ , practically that of an Orthoqraptus. 



Fios. l,i c and d. — Mesograptus r •/ ^ ± 



foiiaceus (Mnrch.). Affinities. — With the exception of Dvplog. pristis, 



His., no species has had so many allied forms referred 

 to it by graptolithologists as Mesog. foiiaceus, a 

 practice which has had a strong justification in the 

 more or less intermediate character of the species 

 itself. M. foiiaceus has been especially confounded 

 with Orthog. calcaratus and its varieties ; the smaller 

 polypary and the more closely set thecse in the 

 former and their progressive change in shape should, 



c. Thecse near the distal end. Meadow- . , ... .. . . . . _. 



town, Liandeiio Flags. Coll. Lap- however, readily serve to distinguish it. It is 



d. Tfcecas near the proximal end, showing probably more closely allied to Olyptog. dentatus, 



SSS^F^ffSScS but its greater breadth and the shape of its theca. 



fig - 8c - show that it is a distinct form. 



Remarks. — The original type specimens of M. foiiaceus (which are preserved in 

 the Museum of the Geological Society of London, and which are figured by 

 us on PL XXXI, figs. 8 a, b) are unfortunately mere fragments. Better 

 examples have, however, been collected by Lapworth and others from the Liandeiio 

 Flags at Meadowtown, Shropshire, whence Murchison's were obtained, but the 

 nature of the rock and the mode of preservation render it extremely difficult to 

 procure satisfactory specimens showing all the specific characters. There can be, 

 however, no doubt that the examples represent a distinct species, and to this 

 Murchison's name should be restricted. 



Horizon and Localities. — Liandeiio Flags, Ardwell Group, Whittery Shales (?). 



Shropshire : Meadowtown ; Wooferton. Wales : Gwern-y-fed-fach, near Builth. 

 S. Scotland, .- Piedmont Glen, Girvan District. 



Associates, etc. — Mesog. foiiaceus is not uncommon in the hard, sub-calcareous 

 Liandeiio Flags of Meadowtown immediately overlying the Liandeiio Limestone, 

 and, so far as known, it has no associates at this locality. Other forms which 

 approach it closely, making allowances for the difference in mode of preserva- 

 tion, are found in the Girvan country (Ardwell Beds), in the Liandeiio Shales, 

 near Builth, and in the Whittery Shales (?) at Wooferton, Shropshire. 



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

 Murchison's types are preserved in the Collection of the Geological Society of 

 London. 



