480 PROCEEDINGS OP THE GEOLOGICAL SOCIETY. [June 7, 



are very small and scarcely perceptible in the upper pleurse, and are 

 stiU short in the middle ones, but become suddenly increased in size 

 in the five hindermost — the third upwards from the tail being 

 longest, reaching as it does for nearly a fourth of its length beyond 

 the extremity of the tail ; the two hindermost pleurse again shorten 

 gradually, the last one terminating just above and in a line with the 

 foremost serration of the tail, to which it is, moreover, for its inner 

 two-thirds, closely compressed. The spines in each case turn sharply 

 backward from the fulcrum, and have tapering extremities ; the 

 upper and middle thinning gradually from the fulcrum, whilst the 

 hindermost first swell out, attain their greatest breadth about midway, 

 and then taper regularly. 



The tail consists of a raised axis of five or six segments, with a 

 broad nearly semicircular serrated limb, and is much narrower than 

 the thorax. The axis reaches backwards nearly to the posterior 

 margin, its last segments, however, being in most cases ill defined. 

 The sides are distinctly marked by furrows and ridges which pass 

 from the central segments to the lateral serrations, and are bounded 

 by a broad raised margin, having concentric lines, and moreover 

 marked by transverse elevations where the lateral ridges (or pleurse) 

 are continued into their terminal spines. There are always three 

 distinct serrations on either side, which diminish gradually back- 

 wards, the last being a little on one side of the line of the axis ; in 

 some cases, however, another is seen still further back, but in all cases 

 the terminal part of the limb is quite free from them. 



Henkt Hicks. 



We may now compare this species, which has long been recognized 

 as distinct by my friend and myself, with A. Henrici, Salter, published 

 in vol. XX. p. 236, from specimens which, wanting the marvellous 

 free cheeks, did not aff'ord us scope for characterizing the genus 



A. Henrici has the glabella twice the proportional width of that 

 of A. Salteri, and the three lower furrows complete across. It has 

 the facial suture reaching even further out in front, so as to include 

 a wider stretch of the margin ; and we do not know of any spinous 

 tips to the front pleurae. The tail is less expanded, more triangular, 

 and has a much broader axis. 



In no genus that I have ever seen do the two portions of the 

 cheeks show so clearly the distinctness of the two segments, anterior 

 and posterior, which form the head of a Trilobite. Separate the ante- 

 rior one with the long eyes in this genus, and you have, to all appear- 

 ance, a complete head left, with a true border to the cheek, such as 

 is possessed by numerous Trilobite genera. I naturally thought that 

 we had in AnopoJenus Heniici (J. c.) a blind Trilobite, and so described 

 it. But further researches in the rocks of St. David's showed us, first 

 fragments, then heads, then bodies, of a form unlike any other Tri- 

 lobite, but clearly enough belonging to the family Olenidce. I de- 

 scribed the genus briefly from these more perfect materials at the 

 Meeting of the British Association at Bath, in 1864, and a short 



