ACIDASPIS ASTEROIDEA. 31 



notice because it agrees precisely with the one figured by Portlock, and possesses the 

 same ornamentation as the head-shields from the Balclatchie Beds referred to this 

 species. The most remarkable feature in the pygidium of L. hihernicns is that 

 whereas the first two pairs of pleurge bear furrows the third pair does not ; and 

 this character led me formerly^ to associate it with the group Metalichas, typified 

 by L. cicatricostis instead of with Amphilichas, of which 1/. dalecarlicus \b the typical 

 example. The lack or obsolescence of the third pleural furrows, however, 

 seems to occur occasionally in Amphilichas, as, for instance, in L. (Amphi.) iningan- 

 ensis, Billings, as shown by Raymond.^ 



In our specimen there is only one complete ring on the axis, and this corresponds 

 with the first pair of pleurae. The second ring is imperfectly defined by a furrow 

 arched backwards and incomplete at the sides, and does not correspond with the 

 second pleurte. The pleural furrows on the first two pleurge are short and less 

 than half their length. All three pairs of pleurce have short, free points ; the first 

 two pleuras are foliate in shape ; the third pair is much broader, and their free 

 points are closely placed in the median line with a sharply acute, narrow notch 

 between them. The axis is not clearly marked off from the long, narrow-pointed, 

 post-axial piece which apparently reaches the posterior notch in the margin 

 separating the third pleura. 



This type of pygidium is quite distinct from that attributed to L. Isevis, 

 Eichwald, by Schmidt^ and regarded formerly by me* (on the strength of this 

 association) as typical of Amphilichas. If we regard the pygidia of L. cicatricosus 

 and L. hihernicus to be of the same structural type, it follows that a parallel 

 development of this part has taken place in the two otherwise distinct sections of 

 the genus, Metalichas and Amphilichas. "We may also doubt now if L. Isevis is 

 referable to the same section as L. dalecarlicus and perhaps should be removed 

 from Amphilichas. 



Family Acidasfibm. 



Genus ACIDASPIS, Murchison. 



Acidaspis asteroidea, sp. nov. Plate V, figs. 3 — 7. 



Specific Characters. — Head-shield broad, transverse, crescentic. Cranidium 

 with straight anterior margin. Free cheeks slightly arched forwards and pro- 

 jecting on each side. Grlabella broadly semi-oval, narrowing anteriorly ; width at 



' Eeed, ' Quart. Journ. Geol. Soc.,' vol. Iviii (1902), p. 74, fig. 7. 



^ Eayuiond, ' 7tli Ann. Eep. Vermont Greol. Surv.,' 1910, p. 232, pi. xxxvi, figs. 1 — 3 (noii 

 p]. xxxix, fig. 14). 



3 Sdiinidt, 'Rev. Ostbalt. Silur. Trilob.,' pt. ii (1885), pi. vi, fig. 10. 

 * Reed, op. cit., p. 80, fig. 18. 



