part 4] upper oRDOViciAisr or the berwyn hills. 495 



This locality may be taken as characteristic of the lowest 

 Ashgillian of the district. It has yielded the following forms : — 



Christiania tenuicincta (M'Coy) ; I Cheirurus sp. 



small form. Abundant. (?) Chromus sp. 

 Orthis (Hebertella) crispa M'Coy. ! Cybele cf. rugosa (Portlock). 



Plectambonites scissa (Davidson). Cybele rugosa var. attenuata Reed. 



Plectambonites quinquecostata Cybele verrucosa (Dalman). 



(M'Coy). i Cyphaspis megalops (M'Coy). 



Rafinesquina subarachnoidea Reed. Illsenus bowrnanii Salter. 



Stropheodonta corrugatella (David- Illsenus sp. 



son). Lichas laxatus M'Coy ; small form. 



Echinosphmra cf. litchi (Forbes). Phacops (Acaste) apiculatusSaltev. 



JEchi nosphserites cf. arachnoideus Phacops (Dalmanites) robertsi Reed. 



Forbes. Phacops fPterygometopusJ brongn- 

 Agnostus aguostiformis (M'Coy). iarti Portlock. 



Calymene cf. blumenbachi var. Phillipsinella parabola (Barrande) ; 



drummoclcensis Reed. very common. 



Calymene aff. quadrata sp. nov. Pemopleurides sp. 



Cheirurus juvenis Salter. Staurocephalus cf. murchisoni 

 Cheirurus octolobatus M'Coy. Barrande. 



Cheirurus cf. pseudohemicranium Trinucleus sp. 



Nieszkowski. 



There are also fragments of many other forms which are too 

 incomplete for determination. 



This may be taken as the typical fauna of the lowest dark 

 mudstones of the Ashgillian of this district. There are, however, 

 a few species which appear to be rare or absent here that are 

 common at other exposures, notably Trinucleus seticomis Hisinger. 



About 15 feet of dark mudstones are seen before they give place 

 gradually to the blue-grey and olive green-grey mudstones of the 

 more normal Ashgillian colouring. The lower part of this series 

 is also highly fossiliferous. The beds are exposed in the bank 

 of the stream on the north side of the ford near Aber Marclmant 

 (al + , fig. 2); also in the road-cutting immediately south-west 

 of the farm. The fauna of these beds is somewhat different from 

 that of the underlying strata, but certainly belongs to the Phillips- 

 inella fauna. Among the fossils found, the following have been 

 identified : — 

 Orthis (sensu stricto) cf. playfairi ' ; Phillipsinella parabola (Barrande). 



Reed. Remopleurides longicostatus Port- 



Plectambonites scissa (Davidson). 

 Strophomena sp. 

 Lichas sp. 



lock (common). 

 Sphserocoryphe thomsoni Reed. 

 Orthoceras cf. audax Salter. 



A marked type of lithology occurs about this horizon, the beds 

 of normal pasty grey-green mudstone becoming full of specks and 

 blotches of dark-blue mudstone. This type of lithology has been 

 found in the lower portions of the Ashgillian throughout the area 

 on the east around Llanfyllin. 



The beds immediately above this speckled zone are usually 

 covered by drift, but in the small valley which runs down to Blaen- 

 y-cwm past Craig Fawr (fig. 3, p. 496) the next succeeding strata 

 are magnificently exposed in an almost continuous section along the 

 bridle-path and on the crags of Craig Fawr. In all this area the 



