AGNOSTUS AGNOSTIFORMIS. 3 



Order III. — Proparia. 



Fa mihj 1. Encrinuridse. 



2. Calymmenidae. 



3. Cheiruridae. 



4. Phacopidse. 



In connection with the examination of the .specimens in the various collections, 

 my thanks are especially due to Mr. E. T. Newton, F.R.S., Dr. John Home, F.K.S., 

 Mr. J. G. Goodchild, and Dr. Smith Woodward, F.R.S. 



SYSTEMATIC DESCRIPTIONS. 



Family Agnostimi. 

 Genus AGNOSTUS, Brongniart. 

 1. Agnostus agnostiformis (M'Coy), 1840. Plate I, fig. 1. 



1846. Trinodus agnostiformis, M'Coy, Syn. Silur. Foss. Ireland, pi. iv, fig. 3, p. 57. 



1848. Agnostus convexus, Salter, e. p., Mem. G-eol. Surv., vol. ii, pt. i, p. 351, pi. viii, figs. 12, 13 



(non fig. 11). 

 1854. Trinodus agnostiformis, M'Coy, Syn. Brit. Pal. Foss. Woodw. Mus., p. 141, pi. i e, fig. 10. 

 — Trinodus tardus, M'Coy, op. cit., p. 142, pi. i e, fig. 9. 



Agnostus trinodus, Morris, Cat. Brit. Foss., ed. 2, p. 99. 

 1864. Agnostus trinodus, Salter, Mem. Geol. Surv., dec. xi, pt. 1, p. 8, pi. i, figs 8 — 10. 



1866. Agnostus trinodus, Salter, op. cit., vol. iii, p. 297, pi. xix, fig. 8. 



1867. Agnostus trinodus, Murchison, Siluria, ed. 4, p. 204, Foss. pi. 46, fig. 6. 

 1873. Agnostus trinodus, Salter, Cat. Camb. Sil. Foss. Woodw. Mus., p. 48. 

 1877. Agnostus trinodus, H. Woodward, Cat. Brit. Foss. Crust., p. 22. 



1879. Agnostus agnostiformis, Nicholson and Etheridge, e. p., Mon. Sil. Foss. Girvau, fasc. ii, p. 200 

 (non pi. xiv, fig. 6). 



Specific Characters. — Head-shield and pygidium subequal, convex, rounded. 



Head-shield forming nearly three parts of a circle or ellipse ; posterior angles 

 contracted and minutely mucronate. Narrow border of uniform width round 

 margin, separated from limb by deep sulcus. Limb of regular width marked off 

 from glabella by sharp continuous furrow. Glabella short, parabolic to sub- 

 cylindrical, slightly constricted about middle, rounded at base, with pair of small 

 transverse basal lobes. 



Thorax unknown. 



Pygidium semi-oval or semi-elliptical ; anterior angles rectangular, not con- 

 tracted. Axis shorter than glabella and subcorneal ov parabolic, rounded ; length 

 less than basal breadth ; furnished with two pairs of furrows; anterior or upper 

 pair oblique, reaching far inwards and separating off a pair of small lobes; second 



