﻿Vol. 66.~] THE ORDOVICIAN OF THE GLENSAUL DISTRICT. 277 



Excrixttrus octocostattts, sp. nov. (PI. XXII, figs. 4 « & 47>.) 



The species of Encrinurus described. by me from ' the gritty ash 

 (322) a third of a mile south-south-west of Shangort,' l in the 

 Shangort Beds, is represented by a well-preserved pygidium from 

 the gritty tuff (62) showing the characters described. But it should 

 be added that the posterior end of the axis is not very well defined 

 in this species, the axial furrows dying out before the tip, and the 

 last two pairs of pleurae bending round behind and merging into it 

 without any distinct furrows between them. The length of the 

 specimen figured here is 9*5 millimetres, and its width at the front 

 end about the same. The first two and the last two axial rings 

 have been destroyed in this example, but the tip of the pygidium 

 is unusually well preserved. If this species is a new one, as it 

 seems to be, the name E. octocostatus may be applied to it. An 

 imperfect free cheek from the same bed (62) possibly belongs to the 

 same species ; the border is strongly convex, rounded and orna- 

 mented with rather distant, small tubercles, and is marked off from 

 the rest of the cheek by a deep, rounded, marginal furrow. The 

 cheek is moderately convex, ornamented with large, coarse, con- 

 spicuous tubercles, and bears a tall conical eye on a short stalk. 



Phacops (Chasmops) aff. odini, Eichwald. 



There are two pygidia in the collection from the tuff (62) which 

 seem closely allied to Ph. odini, Eichw., or may be identical with it. 

 One is nearly perfect, and measures 16 millimetres in length and 

 23 to 24 mm. in breadth ; it shows ten to twelve rings on the axis 

 and eight or nine pleurae on the lateral lobes. The axis is conical, 

 tapering rather rapidly at about 25° or 30° ; the rings are well 

 defined, and show slight lateral swellings. The pleurae of the 

 dependent, and strongly arched, lateral lobes show the usual 

 characters ; there is no distinct impressed line or furrow, but traces 

 of a row of punctae can be made out on their surface. The pro- 

 portions of this pygidium and the number of rings on the axis 

 and of pleurae on the lateral lobes agree very closely with Ph. 

 odini as described by F. Schmidt, 2 who remarks that the pygidium 

 of this species may be compared with that of the Scandinavian 

 Ph. conophihalma, of which there are believed to be British 

 examples. 3 The punctae on the pleurae recall Ph. amphora, Salter, 4 

 from the Llandeilo, but this has more numerous segments. 



Orthis obtusa (Pander), var. 



The small abundant species of Orthis which occurs in the lime- 

 stone (155) may be regarded as a variety of Orthis obtusa 5 



i F. R. C. Eeed, Quart. Journ. Geol. Soc. vol. lxv (1909) p. 147. 



2 'Rev. Ostbalt. Silur. Trilob.' pt. i, Mem. Acad. Imp. Sci. St. Petersb. 

 ser. 7, vol. xxx, no. 1 (1881) p. 99 & pi. ii, figs. 1-13; pi. xi. fig. 16? ; pi. xv, 

 fig. 30. 



3 J. W. Salter, ' Monogr. Brit. Trilob.' (Palaont. Soc. 1864-83) p. 40. 



4 Ibid. p. 42 & pi. iv, fig. 16. 



5 C. H. Pander, ' Beitr. Geogn. Russ. Reich.' St. Petersburg, 1830 p. 87 &. 

 pi. xxvi. fig. 7. 



