182 H. HICKS ON THE SUCCESSION OF 



the underlying Cambrian rocks therefore form the lowest subdivision 

 or Lower Cambrian. For the next subdivision or Upper Cambrian 

 I have hitherto followed Sir Charles Lyell and Mr. Salter by making 

 it comprise the overlying series to the top of the Tremadoc group, 

 but with the qualification now that a considerable portion of what has 

 been called by them Tremadoc should be placed in the Arenig group. 

 The palseontological break at this spot is tolerably strong ; but, with 

 the evidence before us of unbroken succession, it must be confessed 

 that it is scarcely important enough to mark the dividing line 

 between the two great systems known by the terms Cambrian and 

 Silurian ; and yet if it is not placed here, there certainly is no other 

 break below the top of the Bala or Caradoc group which can possibly 

 be looked upon as sufficiently important for that purpose. 



Descriptions of New Species of Fossils from the Arenig Group 

 of St. David's. 



Amptx Saeteri, Hicks. PI. X. figs. 7, 8. 



A. Salteri, Hicks, Cambridge Catalogue. 



This species 1 found several years ago in the flaggy beds to the 

 north of the slate-quarry in "Whitesand Bay ; and I named it after 

 my late lamented friend, Mr. Salter, in the Cambridge Catalogue. 

 It occurs rather plentifully, and it is a very distinct and well- 

 marked species. It is also one of the earliest species of the genus 

 known, being found almost at the base of the Middle Arenig. 



Description. — Nearly 2 inches long without the rostrum, and 

 about ly^- inch wide at the broadest part. Head equal to about 

 one third of the whole length, triangular in shape, and moderately 

 raised ; the glabella occupies about one third of the width, is very 

 wide anteriorly, and tapers backwards from about the junction of 

 the anterior fourth, its sides are indented by oblique and longi- 

 tudinal furrows, which mark off a pair of distinct lateral lobes; 

 rostrum rather more than equal to the whole length of the head. 



The body has a rather narrow axis of six rings. The tail is 

 triangular in shape and strongly margined ; the axis is slightly 

 raised, has three or four rings, and reaches to the hinder border ; 

 the lateral lobes are flattened, and marked with three or four ribs. 



The wide margin to the tail, and the very broad glabella di- 

 stinguish this at once from any other British species. 



Locality and Formation. Slate quarry at "Whitesand Bay, St. 

 David's : Middle Arenig. In collections of D. Homfray, Esq., and 

 H. Hicks. 



Trinttceetjs Etheridgei, n. sp. PI. IX. fig. 6. 



This well-marked species I obtained last summer from the slate- 

 quarry near Llanvirn, and I have much pleasure in naming it after 

 my friend Mr. Etheridge. The cleavage and bedding very nearly 

 coincide in these slates ; and therefore the specimens occur in a 

 tolerably well-preserved state. 



