114 BRITISH CAMBRIAN TRIL0B1TES. 



branch of the facial suture as a double line. The suture forks at the marginal 

 furrow, and the two lines into which it splits reach their maximum separation at 

 the eye. Some specimens also seem to show a similar doubling of the suture 

 behind the eye, but this is always less distinct. Such a duplication of the suture 

 may be observed in other trilobites, but it seems to be particularly conspicuous in 

 A. sedgwicki. 



All the best specimens of Angelina sedgwicki that I have seen are preserved in 

 slate, and are internal casts devoid of the test and more or less flattened and dis- 

 torted. In the Sedgwick Museum, however, there are several specimens (Plate 

 XIII, figs. 9, 10, 12) from more gritty beds at Garth, Portmadoc, which seem to 

 have suffered less from pressure. Unfortunately they are somewhat fragmentary, 

 but they serve to indicate that the general form was rather more convex than it 

 appears in the specimens from slaty beds. 



Horizon and Localities. — Upper Tremadoc : Garth Hill, Ynys Towvn. Tv-hwnt- 

 yr-bwlch, and other places near Portmadoc. 



Genus DIKELOCEPHALUS, Owen. 



The type of Dikelocephalus is D. minnesotensis, Owen, but the name has been 

 somewhat loosely applied to many forms which differ too greatly from that species 

 to be properly included in the same genus. Recently, however, in a memoir 1 on 

 " Dikelocephalus and other genera of the Dikeloeephalinre," Walcott has subjected 

 the whole group to a careful revision, and it is accordingly unnecessary for me to 

 discuss the true limits of the genus. 



The head is transverse, with the genal angles produced into spines. The 

 glabella is subquadrate, narrowing slightly towards the front, which is broadly 

 rounded ; the posterior pair of glabellar furrows is strong and continuous across, 

 though somewhat shallower towards the middle; the middle pair is short, and the 

 anterior pair shorter still or absent altogether ; the neck-furrow is strong. The 

 eye is rather large, crescentic, placed near to the glabella and to the occipital 

 furrow. The facial sutures meet on the upper surface a little behind the extreme 

 front of the head, forming either an obtuse angle or else a continuous curve; from 

 there they run outwards and slightly backwards, then bend inwards to the anterior 

 extremity of the eye, pass round the palpebral lobe, turn almost directly outwards 

 and finally curve backwards to the posterior margin, which they cut at a consider- 

 able distance from the genal angle. The tail is large ; in outline the anterior 

 border forms a curve which is convex forwards, and the antero-lateral angles are 

 rounded off; the posterior border may or may not have two postero-lateral spines; 

 the axis is much narrower than the lateral lobes and ends bluntly before the 



1 Smithsonian Misc. Coll., vol. lvii, no. 13 (1914). 



