54 F. R. Coivper Reed — ISfew Bala Trilohites. 



cast of the lower surface of the fringe (Fig. 5) it is seen tliat there 

 are only two pits present in each sulcus, and that these do not fuse 

 together in the few last radial sulci on each side as the corresponding 

 ones do on the upper surface, whereas in the anterior radialsulci on 

 the lower surface the two pits approximate or even tend to fuse into 

 one. There is also seen on the lower surface a marked smooth space, 

 nearly equal in width to the sulci, running behind them in a pointed 

 arch and separating them from a single series of small pits which 

 do not show on the upper surface. The median front portion of this 

 series is situated on a triangular depressed area which posteriorly is 

 extended into narrow vertical prolongations, separated from the rest 

 of the fringe by a continuation of the unpitted space. These 

 prolongations, which are in fact the upwardly-bent inner margins 

 of the fringe, decrease in width till they end at the base of the 

 genal spines and bear the single row of small pits. What appears, 

 therefore, in the impressi(ni as a cushion, corresponds to an actual 

 concavity on the lower surface of the fringe. The genal or lateral 

 spines start from the outer posterior angles of the head-shield ; each 

 spine is stout at its base, but tapers rather rapidly to a point ; it is 

 also grooved along its whole length and has an outward curve. 

 As far as I can draw conclusions from the fragmentary material at 

 present at my disposal the spines in the male are longer than those 

 in the female. The degree of outward curvature is also liable to 

 variation. 



The thorax with its six body-rings has the axis sti'ongly convex. 

 The pleurae are horizontal as far as the fulcrum, but are at that point 

 bent gently downwards and slightly backwards. The fulcrum is 

 situated at a distance from the axis of rather less than two-thirds 

 the whole length of the pleura. A shallow furrow starts from the 

 anterior inner angle, and runs to the outer posterior angle of each 

 pleura, increasing in breadth as it is traced outwards. It is bordered 

 in front by a narrow rounded margin of constant width which is 

 formed by the raised anterior edge of the pleura. The posterior 

 part of the pleura is abruptly elevated behind the oblique furrow, 

 but slopes down gently to the posterior margin. In the extra- 

 fulcral portion the furrow occupies nearly the whole width of the 

 pleura. The free ends of the pleurge are truncate. 



The pygidium, which is about one-third the length of the headj 

 shield, is rounded and transversely expanded (being nearly three 

 times as broad as long), and has a moderately convex axis occupying 

 in breadth about one-fifth of the surface. This axis tapers slightly 

 to an obtuse end which almost touches the posterior margin, and is 

 crossed by three or four faint annulations. Two to four indistinct 

 grooves are visible on the lateral lobes of the pygidium, the broad 

 posterior border of which is sharply bent down. 



Affinity. — The figures in Angelin's " Paleeontologia Scandinavica " 

 (Trilohita, t. xli. figs. 1, la, h, c, p. 84) of Trinucleus buccidentus 

 (Aug.), if they had been supplemented by a more minute description, 

 would have enabled us to institute a more exact comparison than is 

 now possible ; for undoubtedly the Irish form approaches more 



