LOWER PALAEOZOIC HYOLITHLD^E FROM GIRVAN. 209 



Hyolithes penkillensis, sp. nov. (PI. II. figs. 3-5.) 



Shell straight, short, broad, rapidly tapering at about 1 in 1\. Ventral face low, 

 angulated (imperfectly known). Dorsal face flattened or very weakly convex, with 

 narrow border distinctly marked off by groove, and with 1-3 strong, submarginal, 

 longitudinal lines. Mouth with dorsal lip strongly arched. Lateral edges acute, sharp. 



Dimensions : — 



I. II. 



Length ... ... 15*0 mm. ll'O mm. 



Width at mouth . . .6-5,, 55 „ 



Horizon and Locality. — Penkill Group, Penkill. 



Remarks. — This broad, short form has much the shape of H. tardus, Barr., # from 

 Stage G, but the margins of the dorsal face have the characters of H. norwegicus, 

 Kjerulf.t H. obvius, Barr.,} from Stage E, tapers less rapidly to the point, and does not 

 show the narrow borders on the dorsal face, as does the Girvan form. 



There is one specimen in the Hunterian Museum referable to this species from the 

 same locality, but it tapers rather more slowly, measuring 17 mm. in length and 

 6 '5 mm. in width at the mouth. 



Hyolithes subcrispatus, sp. nov. (PI. II. figs. 6-8.) 



Shell short, broad, straight, tapering rapidly at 1 in 2^. Dorsal face flattened, very 

 weakly convex. Lateral angles sharp, acute. Ventral face unknown. Mouth with 

 dorsal lip strongly arched. Surface of dorsal face crossed by strong, rounded, fairly 

 regular and equal concentric growth-ridges or striae, and marked by 20-25 regular, 

 straight, equal and equidistant raised thread-like lines, separated by broad interspaces. 

 Occasionally two of the longitudinal lines seem more strongly developed, and divide the 

 dorsal face into three equal longitudinal areas. 



Dimensions : — 



I. II. 



Length ...... 24 mm. 21 mm. 



Width at aperture . . . . 10 ,, 8 ,, 



Horizon and Locality. — Drummuck Group, Thraive Glen. 



Remarks. — This shell has more the shape and ornamentation of H. decipiens, Barr.§, 

 but not such marked cancellation of the surface, nor a bent tip. H sulcatulus, Nov.,|| 

 has a more slender shape and fewer longitudinal ribs. 



* Barrande, op. cit., p. 93, pi. vi. figs. 17-18 ; Novak, op. cit, p. 27, pi. iv. figs. 33-36. 



t Holm, op. cit., p. 87, t. iii. figs. 1-5. 



| Barrande, op. cit., p. 86, pi. xii. figs. 1-6. 



§ Barrande, op. cit., p. 80, pi. xii. figs. 33-37 ; Novak, op. cit., p. 16, t. iii. figs. 25-28. 



|| Novak, op. cit., p. 26, t. iii. fig. 22. 



