30 TRILOBITES OF GIRVAN. 



agree with the Swedish in these respects. T. angelmi, Linnarsson, 1 seems to bear 

 a closer resemblance to the common American form, T. becki. T. pygm&us, Torn- 

 quist, 2 from the Trinucleus-Shales of Enan, has the lateral furrows more oblique 

 and the frontal lobe larger, and T. jemtlandicus, Linnarsson, is quite distinct. 3 



Collection.— Mrs. Gray (f. M.) 



Horizon and Locality. — Balclatchie Group (Llandeilo) : Balclatchie; Balclatchie 

 Conglomerate. 



Genus APATOKEPHALUS, Brogger. 

 1. Apatokephalus, sp. Plate IV, fig. 9. 



1879. Gheirurus? sp. mil. a, Nicholson ami Etheridge, Mon. Silur. Foss. Girvan, fasc. ii, p. 203, 

 pi. xiv, fig. 11. 



Specific Characters. — Pygidium subquadrate, longer than wide; front margin 

 almost straight ; sides subparallel ; posterior margin truncated and furnished with 

 three pairs of short blunt points separated by shallow subangular notches (in one 

 of the specimens in the Museum of Practical Geology there seem to be only two 

 pairs of points). Axis convex, conical, pointed, tapering rapidly, rather more than 

 half the length of the pygidium and one third its breadth at front end ; composed 

 of seven or eight rings, of which only the first four or five are distinct. Lateral 

 lobes flattened, horizontally extended, equal in width to axis at front end ; composed 

 of three pairs of unfurrowed pleurae bending sharply backwards at a short distance 

 from axis and produced to form short projecting triangular points on posterior 

 margin. First pair of pleurae narrows posteriorly; second pair is of nearly uniform 

 width ; third pair is shorter and broader and in contact in middle line behind axis. 



Remarks. — This minute pygidium. from Balclatchie in Mrs. Gray's collection 

 was figured by Nicholson and Etheridge as Gheirurus? sp. ind. a; but it is scarcely 

 necessary to point out the features by which it differs from this genus ; for no 

 species of the latter has a pygidium with at all the same characters. The type 

 shows more than their figure represents, for the posterior margin is preserved. 

 With the additional light thrown by the examination of other examples of the 

 same form (lie true generic position can be determined. 



Affinities. — From Bemojpleurides radians, Barr., 4 it differs in having too many 



1 ' Vestergot. Camb. Silur. Aflagr.,' p. 70, pi. ii, fig. 28 ; Brogger, ' Die Silur. Et. ii anil iii,' p. 112, 

 pi. iii, fig. 1. 



-' Tornquist, ' Siljaus. Trilobitf.,' p. 38, pi. i, fig. 40 (1884). 

 Winian, "Palaont. Notiz. No. 3," 'Bull. Geol. Instit. Upsala,' No. 11, vol. vi, pt. 1 (1902), 

 p. 79, pi. v, figs. 5—8. 



1 Barraade, ' Syst. Silur. Boheme,' vol. i, p. 350, pi. xliii, figs. 33 — 39. 



