G BRITISH FOSSILS. 



Cefii Llwydlo, north of Llandovery (J. W. S.) Everywhere in upper 

 Silurian rocks, Herefordshire and Shropshire (Murchison, " Sil. Syst.") 

 Especially abundant in Dudley limestone and shales. Usk, Monmouth- 

 shire ; in Ludlow and Wenlock rocks (J.W. S.) Horse-shoe Farm, Tort- 

 worth ; Huntly-hill, Gloucestershire ; Caradoc sandstone ; Woolhope 

 limestone and upper Silurians of Woolhope, Abberley, and Malvern 

 districts. (Geol. Surv.) Not yet found in Ireland. 



Var. /3. Marloes Bay, and St. Ishmael's, Pembrokeshire (Phillips). 

 Cwmdwr, Brecknockshire ( J. W. S.). Brindgwood Chase, in Ludlow rocks ; 

 Burrington, in Wenlock shale ; near Ludlow, Aymestry, and Nash Scar, Here- 

 fordshire (" Sil. Syst.") Usk, Monmouthshire, from Wenlock shale to 

 upper Ludlow rock ; Abberley and Malvern (Phillips). 



Foreign Distribution. In Gottland, upper Silurian, rare (Dalman 

 and Hisinger.) Ripley, Ohio (Green ; the localities quoted from 

 Canada are erroneous, Dr. Bigsby's specimens being of quite different 

 species, but one, which is probably the true species, was found by him 

 at Gaspe, Gulf of St. Lawrence). 



EXPLANATION OF PLATE I. 



Fig. 1. Perfect specimen, in Mr. Tennant's cabinet, probably from Dudley. 



Fig. 1 a. Front view of head ; 1 b, side view. 



Fig. 2. Same, dissected ; a, front lobe or forehead ; b, spira or neck lobe ; c, cheek or 

 wing ; d, margin ; e, axis of body ring ; /, fulcrum of ditto ; g, part of the axis of a tuber- 

 culated specimen ; k, intermediate ribs of the tail. (These are the indications of separa- 

 tion between the segments.) The g at the tail margin should be omitted. 



Fig. 3. Hypostome from Ledbury. 



Fig. 4. Magnified view of surface of eye, the cornea tuberculate between the convex 

 portions which cover the lenses. At (a a), some small abortive lenses are seen. Ledbury. 



Fig. 5. A cast of the interior of the eye, the cornea having been removed, and the 

 lenses fallen out. Vinnal Hill, Ludlow. 



Fig. 6. An eye, with very prominent lenses, which are partly visible, where the cornea 

 has been broken away. Ledbury. 



Fig. 7. A fine young specimen, with rather prolonged tail. Dudley, Cabinet of Mr. 

 John Gray. 



Fig. 8. Specimen, with vastly prolonged head spines. Dudley Museum. 



Fig. 9. Head, with produced front (male ?) Bodenham, Woolhope. 



Fig. 10. Cheeks united across the front, and separated from the rest of the head along 

 the facial suture. The course of the suture beneath (at a) is rather different from that of 

 the upper side. Vinnal Hill, Ludlow, a rich locality. 



Fig. 11. Tail, with the axis narrow and the point prolonged. Intermediate between 

 P. caudatus and the var. lo?igicaiidatus. Vinnal Hill. 



Fig. 12. Tail of ordinary form. From Wenlock limestone of Clincher's Hill, South 

 Malvern. 



Fig. 13. Tail of var. /3, longicaudatus. Craig-y-Garcyd, Usk, in Wenlock shale. 



Fig. 14. Head of same variety. Burrington, Ludlow. 



Fig. 15. Tuberculated (diseased?) tail, with very narrow border. Rock Farm, May 

 Hill. 



Fig. 10. Accidentally introduced; it belongs to the species next described. Long's 

 Quarry, Tortworth. 



