8 TRILOBITES OF GIRVAN. 



and the marginal spines on the pygidium are absent. It, may also be added that 

 the posterior angles of the head-shield are not contracted, giving a different outline 

 to the head, and that the central tubercle on the second axial segment of the 

 pygidium is in the form of an elongated ridge extending from the front border to 

 the second transverse furrow. In A. agnostiformis this axial tubercle is isolated, 

 and is placed across the second transverse furrow, which is thus interrupted by it. 



Collection. — Mrs. Gray. 



Horizon and Locality. — Whitehouse Group (M. Bala) : Whitehouse Bay. 



Family Haepedtda 

 Genus HARPES, Goldfuss. 

 1. Harpes flanagani, Portlock, 1843. Plate II, figs. 12, 12 a. 



1843. Harpes flanaganni, Portlock, Gool. Eep. Londond., p. 2G8, pi. v, figs. 5 a, 5 b, 6, 7. 



1854. Harpes flanaganni, Morris, Cat. Brit. Foss., ed. 2, p. 109. 



1872. Harpes flanagani, Murchison, Siluria, ed. 5, p. 206, Foss., pi. 48, fig. 4. 



1877. Harpes flanaganni, H. Woodward, Cat. Brit. Foss. Crust., p. 37. 



1899. Harpes flanagani, Reed, Quart. Journ. Geol. Soc, vol. lv, p. 745. 



Remarks. — There are two complete "horseshoe" limbs and some fragments of 

 this species of Harpes from Ardmillan which have come under my notice; the larger 

 one measures 21 mm. in length, and is in Mrs. Gray's collection; the smaller one 

 measures about 13 mm. in length, and is in the Museum of Practical Geology. 

 Another perfect example of about the same size as the latter comes from 

 Balclatchie, and a fragment of a limb from Craighead may also belong to the same 

 species. There is also a portion of a limb and cheek from Dow Hill. 



The " horseshoe " is subquadrate in form, being nearly as wide as long and 

 somewhat flattened in front; the inner margins of the arms are nearly parallel, but 

 the ends, which are acutely pointed, bend slightly inwards. The limb itself is 

 slightly excavated on the upper side, but is horizontally extended, and is closely 

 covered with small circular pits, not arranged in any definite order. Inside the 

 narrow smooth raised outer border is a single row of larger pits, and this row 

 exists found the whole free arms of the limb. The cheek (as seen in the fragment 

 from Dow Hill) is strongly convex and rises steeply from the limb, from which it is 

 separated by a narrow smooth band, bordered on both sides by a single irregular 

 row of pits of larger size than those covering the limb. The cheek, which bears on 

 its summit a small prominent stalked eye, is marked by rows of minute pits closely 

 sel in regular radiating lines, but the posterior lateral angle of the cheek has on 

 its basal slopes pits like those on the limb. The shape of the "horseshoe" and 



