2 



BRITISH FOSSILS. 



remote from it. The hinder angles of the head with the spines 

 abrupt, short, scarcely reaching the fourth segment, directed back- 

 ward, not outward as usual in the sub-genus. 



Body rings 15 (our artist has only represented 14 rings), their 

 axis convex, nearly as broad in all the rings as the pleurge, which 

 decrease regularly, not abruptly, in length from before backwards ; 

 they are obliquely pointed, with short spines directed outwards, but 

 very little backward. The fulcrum of the pleurae is placed beyond 

 the half, even in the hinder rings. 



Tail short, semi-oval, with a very wide axis, of three rings, and 

 the sides with two furrows. 



0. micruTUs is easily distinguished from 0. cataractes by the 

 oblique lower glabella furrows, the shape of the small smooth sub- 

 truncate tail, and by the abrupt narrowing of the hinder body 

 rings, which also have the fulcrum placed nearer than half way out 

 from the axis. The tail is even more easily distinguishable, the 

 width of the axis being greater than that of the sides, and having 

 three rings, including the terminal portion ; there are two lateral 

 furrows, not one only. 0. cataractes has 15 body rings. 0. mi- 



CTUTUS 14. 



The head is much like that of 0. micrurus, but tlie lower glabella 

 furrows run quite across. Compared with the Swedish 0. trun- 

 catus, the greater breadth of the cheeks, and the longer, more 

 parabolic form of the glabella, will distinguish it. I do not compare 

 the caudal portions, for Angelin's figure looks as if there were some 

 mistake in this part. Possibly two of the caudal rings as figured 

 by him belong to the body, which otherwise would have but 13 

 rings — a difference hardly to be expected in such closely allied 

 forms. 



0. truncatus is, I think, from higher beds, at Andrarum in 

 Scania, than our Lower Lingula flags, but this is a point not 

 yet sufficiently investigated. 



Localities and Geological Position. — Lower Lingula Flags, 

 Maentwrog Waterfall, Merionethshire, in black shaly strata full of 

 Agnostus ijrinceps ; also at Treflys, E. of Criccieth, Carmarthenshire 

 N. Wales, where I found the figured specimen in 1859. Specimens 

 probably identical are found at the Dolgelly gold mines. 



