116 Wyatt-Edgell — The Arenig and Llandeilo Groups. 



The Upper subdivision is also seen at Abereiddy Bay, Pembroke- 

 shire, in the form of dark slate, and black shale with graptolites. 

 (The two most common species found in this shale, viz. Didymo- 

 grapsus MurcMsoni and Diplograpsus pristis, occur also at Builth, 

 where they mark the bottom beds of the Upper Llandeilo, just as 

 they do at Abereiddy. This fact may be of importance.) 



The Lower subdivision, on the other hand, occurs as sandy flag- 

 stones with large beds of limestone at Llandeilo, also at Narberth, 

 Pembrokeshire ; often it contains trap and volcanic deposits (men- 

 tioned before). In a section near Llandeilo, published in " Siluria" 

 (p. 57), the Lower Llandeilo is made to overlie what I suppose is 

 the Bala limetone of Bird's Hill. Perhaps it is faulted against it. 



Besides the one near Builth made by the Geological Survey, there 

 is a section of the whole Llandeilo group near Llangadock published 

 in " Siluria" (p. 58). Here the Upper Llandeilo, full of 'Graptolites, 

 is represented by shales thrown up into an anticlinal over the Lower, 

 seen as bedded trap, flags, and limestone. 



The characteristic fossil of the whole Llandeilo series is undoubt- 

 edly Ogygda BucML It is, however, of a greater size and commoner 

 in the upper subdivision ; in the lower it is represented by a 

 smaller and more convex variety, with but eleven side-ribs to the 

 tail. This variety was recognized by Mr. Salter some time since, 

 and the name convexa was proposed for it. 



Asaphiis tyrannus and the nearly allied Asaphus peltastes are found 

 everywhere in the Lower Llandeilo, associated with the variety of 0. 

 Buchii just mentioned. These, with Calymene Camhrensis and Trinu- 

 ■cleus favus, are fossils quite peculiar to this zone, not found in the 

 upper subdivision. Lichas patriarchus is a new species, of which 

 my description was published in the Geological Magazine for 

 April, 1866, Vol. III. p. 160. The OpMleta or Helicotoma, -mentioned 

 in the list, is from Fairfach, near Llandeilo. Lingula gramdata is a 

 characteristic fossil of this stratum. OrtMs calligramma is found in 

 the volcanic grit near Builth, and OrtMs striatula at Llandeilo and 

 Narberth. Associated with Asaphus peltastes, is a small Ctenodonta, 

 not uncommon in the limestone of Dynevor Park, Llandeilo ; this 

 completes the list of the common fossils from the Lower beds. 



The genus Asaphus is represented in the Upper Llandeilo by the 

 A. Corndensis^ of Murchison, which is common at Gilwern, near 

 Builth. This is the only species that I know of. The large many- 

 ribbed variety of 0. Buchii is eminently characteristic ; cuilously 

 distorted specimens of it are found in the slates of Abereiddy Bay. 

 The genus Barrandia, of which there will be four described species 

 when the next volume of the Palceontographical Society appears, is 

 peculiar to this zone. Calymene duplicata is a common fossil, and 

 everywhere accompanies the ordinary variety of 0. Buchii. Cheiru- 



' Asaphus Corndensis belongs to the subgenus Ftychopyge of Angelin, wbich bas 

 certainly more tbe appearance of an Asaphus than of an Ogygia. Tbe form of the 

 labrum seems too yariable in the AsaphidcB to be considered a generic distinction. — 

 H.W.E. — (See Mr. H. Wyatt-Edgell's paper " On the Genera Asaphus and Ogygia, 

 &c." Geological Magazine, January, 1867, Vol. IV. p. 14.— Edit.) 



