186 H. HICKS ON THE SUCCESSION OF 



our Upper Arenig. The present species was found in the Llanvirn 

 quarry, and is therefore also of Upper Arenig age. I have named it 

 after my friend Mr. Homfray, to whose researches in these older 

 rocks we are greatly indebted. 



Description. — Nearly 2 inches long, and 1| inch wide. The head 

 is incomplete ; but the glabella is seen to be wide, not furrowed, 

 and separated from the cheeks by very faint axial furrows. The 

 axis of the thorax is very wide anteriorly, and tapers sharply towards 

 the tail. The anterior pleurae are only equal in length to about two 

 thirds of the opposite rings of the axis ; but the hindermost ones are 

 half as long again as the width of the axis at that part. The pleurae 

 are flat and grooved for about one third of their length, the fulcrum 

 being very near the axis ; they are also sharply pointed, and their 

 whole surface is ornamented with fine lines. The tail is twice as 

 wide as it is long, and the front arched ; the axis is short and conical, 

 prominent at the tip, and with one furrow ; the lateral lobes 

 moderately raised, with the whole surface ornamented by tolerably 

 strong lines. 



This is a very well-marked species, and it differs in several parti- 

 culars from the other species hitherto known. The axis is wider at 

 the upper part, and it tapers more regularly than in B. Cordai, 

 the species which approaches nearest to it ; the glabella also is much 

 wider than it is in that species. 



Locality and Formation. Llanvirn Quarry : Upper Arenig. 



Placopakia cambeiensis, n. sp. PI. IX. figs. 1, 2. 



This interesting species is the first of the genus found in this 

 country, and was obtained by me from the Llanvirn quarry in August 

 last. It resembles in some respects the Placoparia Zippei, Corda, 

 found in Prance, Spain, and Bohemia, but is yet distinct, and it is 

 also a smaller form. It is an important link in connecting the 

 British with the Continental Silurian faunas ; and it occurs also at 

 about the same horizon in each country. 



Description. — Ovate in shape, 1J inch long and about J of an 

 inch wide. Head semicircular and rather more than a fourth of 

 the whole length; glabella very broad in front, occupying more 

 than one third of the width of the head, and reaching the inner edge 

 of the anterior margin, convex, minutely punctate and marked with 

 three strong lateral furrows, besides the neck-furrow, the lowest 

 being directed obliquely backwards until it nearly reaches the neck- 

 furrow. The axial furrows are deep ; the cheeks triangular, convex 

 and rather deeply punctate. Eyes small, situated close to the glabella, 

 and near the anterior margin ; the posterior facial suture cuts across 

 the margin at the outer angle, which is rounded. Thorax com- 

 posed of twelve rings, and strongly trilobed ; axis rather less than a 

 third of the width, and tapering gradually towards the tail from about 

 the sixth segment; pleurae convex, with the fulcral point situated 

 near the middle, extremities pointed and directed outwards. The axis 

 of the tail consists of four or five strongly convex rings, and tapers 



