ASAPHUS (ISOTELUS) GIGAS. 45 



Glabella oval, truncated at base, tuberculated ; no lateral furrows. Axial furrows 

 deep, distinct, arched, surrounding glabella. Occipital furrow well marked, 

 straight. Occipital ring well developed, elevated as high as glabella, provided with 

 strong median spine inclined backwards. Cheeks triangular, rounded, smooth, 

 widest near front. Narrow flattened border of almost uniform width extends round 

 cheeks and front of head-shield, where are two small downwardly bent spines. 

 Thorax unknown. Pygidium semicircular, strongly arched. Axis convex, conical, 

 rounded, one third the width of the pygidium and extending two thirds its length ; 

 three segments, of which the last two are scarcely separated. Lateral lobes smooth, 

 not segmented, inclined downwards. Narrow flattened border round margin. 



Remarks. — Only the head-shield is known from the Girvan area, and three 

 imperfect specimens have come under my notice. These are flattened by pressure; 

 the glabella seems to be subquadrate in shape ; the neck-spine is preserved in one 

 specimen, but the anterior marginal spines are not visible. 



This peculiar and imperfectly known trilobite occurs in the beds of Whitehouse 

 Bay in association with Gyclopyge rediviva, G. armata, Dionide richardsoni, etc. In 

 Bohemia it occurs on the same horizon with the same two first-mentioned species 

 and with Dionide formosa, which is closely allied to D. richardsoni. 



Linnarsson 1 identified T. wegelini with T.fractus, and Tornquist (ojp. cit.) records 

 the species from the Trinucleus -Shales of Sweden. 



Collection. — Mrs. Gray. 



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



Family Asafhhxzb. 

 Genus ASAPHUS, Brongniart. 

 1. Asaphus (Isotelus) gigas, De Kay, 1824. Plate VII, fig. 1. 



? 1823. Asaphus platycephahis, Stokes, Trans. Geol. Soc. Loud., ser. 2, vol. i, p. 208, pi. xxvii. 

 1824. Isotelus (j'ujas, De Kay, Aim. Lyceum Nat. Hist. New York, vol. i, p. 170, pi. xii, fig. 1. 

 1820. Asaphus (jujas, Dalman, Palsead., p. 70. 



Asaphus planus, Dahnan, ibid., p. 70. 

 1832. Isotelus ylgas, Green, Mon. Trilob. N. Amer., p. 71, casts 21, 22. 



— Isotelus planus, Green, ibid., p. 08, east 23. 



— Isotelus stecjops, Green, ibid., p. 71, casts 20, 27. 

 Brongniartia isotelea, Eaton, Geol. Text-book, p. 33, pi. ii, tig. 22. 



1835. Asaphus platycephalus, Broun, Leth. Geogn., vol. i, p. 115, pi. ix, Ii- 8. 

 1840. Isotelus gigas, Milne Edwards, Crust., vol. iii, p. 298. 



— Asaphus plat tjcephalus, Bucklaud, Geol. and Mill., vol. ii, p. 70, pi. xiii, fig. 12. 



Linnarsson, ' Jemtorel. mel. d. silur. Aflagr. i Dalarne,' p. 350 (1871). 



