28 SILURIAN TRILOBITES. 



This is smaller than the typical variety, seldom more than one inch long, and has a 

 different aspect, from the rounding of the front and the greater convexity of the forehead- 

 lobe. The glabella has nearly parallel sides, as in the typical form ; the front furrow is 

 not stronger than the rest, but is rather more sigmoid. The middle furrows reach the 

 side of the glabella ; the neck-segment is prominent and has a distinct tubercle. The 

 eyes are small, with about 130 lenses, and placed very near the glabella. 



The axis of the body is convex ; the pleurae more tumid between the grooves than usual. 

 Some young specimens have larger eyes in proportion, and the front furrows obscure. 



But these variations with larger or smaller eyes, more distinct or less dis- Fig. 8. 

 tinct glabella-furrows, &c, occurring as they do both in the angulated and /jC^k 



rounded varieties, oblige me to consider them as of the same species, though sSg|» 



the characters above given show that we are dealing with a very distinct ingia, var. & 



• , z . cuneatus, from 



Variety Or Sub-species. Llanrwst near 



There is yet another variety, which might be called var. I, cuneatus. Fig. 8. 



Localities and Geol. Range. — The ordinary variety a is found from the May Hill 

 Sandstone to Upper Ludlow Rock. May Hill Rocks; Pembrokeshire; Norbury and 

 Bogmine, Shropshire. Woolhope Limestone and Wenlock Shale ; Malvern, many 

 localities ; Burrington, Shropshire ; Usk, Monmouthshire ; near Llanrwst, and many places 

 in the Denbighshire grits, N. Wales. Pembrokeshire and Carmarthenshire, S. Wales. 

 Wenlock Limestone of Dudley, Wallsall ; Benthall Edge ; Malvern ; Abberley, &c. 

 Ludlow Rocks, Lower and Upper ; Shropshire ; Carmarthenshire ; Pembrokeshire. 



The varieties |3, y, above described, are as yet only known from the Wenlock Rocks ; 

 variety y only from the Wren's Nest and Malvern ; but the variety $ is from Upper 

 Ludlow strata, Whitcliff, Ludlow (Mr. Edgell's cabinet) ; and the species or variety t, con- 

 sirictus, only from the Wenlock shale, of Dudley, Wallsall, and especially Malvern. Var. £ 

 is from the Denbighshire grits of Llanrwst, near Conway. (Woodw. Mus.) 



Foreign distribution. — Nova Scotia, in Upper Ludlow rocks. 



P. (Acaste) apiculatus, Salter. PI. I, figs. 36 — 38. 



Phacops apiculatus, Salter, in Prof. Sedgwick's Synopsis Classific. Pal. Rocks, 



fasc. 2, Appendix iii, pi. i g, figs. 17 — 19 (1852). 

 Portlockia apiculata, M'Coy. Ibid. (1851), fasc. 1, 162. 



Phacops apiculatus, Salter. Memoirs Geol. Surv., Decade vii, art. 1, p. 9. (1853.) 

 — — id. Siluria, 2nd ed. (1859), p. 75, Foss. 13, f. 2. 



P. {Acaste) omnino P. Downingia simillimus, sed capite longiore. Glabella elongata 

 untice convexior, lobis basalibus circumscriptis subtrigonis nee iransversis ; sulco mediano 

 longiore, supremo distincto. Oculi elotigati depressi. Anguli capitis brevissime mucronati. 

 Cauda ad apicem compressa ct in apiculum recurvum brevem producta, axi angusto. 



Heads and caudal pieces of this small species are not uncommon in the Caradoc rocks 



