I. 



II. 



21-0 mm. 



16'0 mm. 



18-0 „ 



15-0 „ 



5-0 „ 



4-0 „ 



lo-o „ 



8-5 „ 



3 been recorded on several 



Isles, but 



Schmidt (' Rev. 



AMPYX HORNEI. L9 



Dimensions. — 



Width of middle-shield at base 



Length of head to base of spine (about) 



Width of glabella at base . 



„ „ across middle 



Remarks. — The species Ampyx rostratus, Sars, ha 

 occasions and from several localities in the British 

 Ostbalt. Silur. Trilob.,' pt. iv, 1804, p. 85) has some justification in doubting 

 whether Sars' species really occurs in Britain. Certainly the Girvan specimens 

 from the Drummuck beds which have been attributed to it show some important 

 points of difference, and their characters appear to indicate a new species which 

 may be termed A. drwmmuckensis. Nicholson and Etheridge's diagnosis of 

 .1. rostratus is based on these Girvan specimens, which show some minor points 

 of difference amongst themselves, but these are found by the examination of further 

 material to be largely due to their state of preservation. The above is an amended 

 description of this new species. 



Affinities. — The punctate surface at once serves to distinguish this species 

 from A. rostratus, Sars, which is smooth (Pompecki, 'Trilob. Ost.-westpreuss. 

 Diluv-gesehieb.,' 1890, p. 16). But there are also other points of difference, such 

 as the two pairs of pits in the front part of the axial furrows, the pair of transverse 

 grooves near the base of the glabella, the weakly sigm.oid.al, less oblique facial 

 sutures, the smooth lateral lobes of the pygidium, etc. There can, however, be 

 no doubt that this Girvan species is closely allied to A. rostratus. An interesting 

 enrolled specimen of a nearly perfect individual from the Starfish Bed is iu 

 Mrs. Gray's collection and is here figured (PL III, fig. 5). 



Collections. — Mrs. Gray (f. M., pi. xiii, figs. 1 — 3) ; Museum of Practical Geology 

 (f. M., pi. xii, figs. 14, 15) ; Edinburgh Museum. 



Horizon and Localities. — Drummuck Group (U. Bala): Drummuck; Thraive 

 Glen. Starfish Bed : Thraive Glen. 



3. Ampyx hornei, Nicholson and Etheridge, L879. Plate III, figs. 8—10. 



r L876. Ampyx mammillatus, Armstrong and Young, Cat. West. Scot. Fuss., p, 1">. 



1879. Ampyx hornei, Nicholson and Etheridge, Mon. Silur. Fuss. Girvan, fasc. ii, p. 184, pi. xiii, 

 figs. 4—8. 

 ? 1879. Asaphus, sp., Nicholson and Etheridge, ibid., p. 154, pi. x. fig. 20. 



1899. Ampyx hornei, Mem. Greol. Surv., Silur. Rocks Brit., vol. i, Scotland, pp. 509, 672, 688. 



Specific Characters. — Head-shield broadly semicircular, more than twice as broad 



