34 SILURIAN TRILOBITES. 



wards ; the rest are short and rounded, the base-lobes narrow, the neck-segment 

 prominent. 



Cheeks very convex, separated by deep axal furrows from the glabella, strongly cir- 

 cumscribed in front by the deep marginal furrow, and behind by the neck-furrow ; the 

 angles rounded, not spinous? Eyes prominent, small, curved, somewhat sunk, overhung 

 •by the angles of the glabella. 



Of the tail Ave have but few specimens ; our largest is that figured in Professor 

 Sedgwick's work. It is semicircular and very convex? with a broad, prominent axis 

 reaching nearly the whole length, and blunt at the apex ; ringed throughout by eight or 

 nine ribs, and with no smooth terminal portion. The sides are also convex, with about 

 eight simple, radiating ribs, not much curved, and with no intermediate furrows. The 

 ribs abut abruptly against a narrow but distinct margin. The other tail (fig. 34) is less 

 certainly of this species, but is found associated with it. It has a wider margin, and only 

 seven lateral furrows. 



Localities. — Caradoc rocks, North "Wales; at Capel Garmon, near Llanrwst ; also at 

 Penmachno, and Pont-y-Glyn Diffwys, near Corwen ; and near Llangynnog, in Mont- 

 gomeryshire. (Mus. Pract. GeoJ. and Woodw. Mus.) 



Phacops (Acaste) Brongniarti, Portlocl: PI. I, figs. 20 — 25. 



$ 1 P. Brongniarti, Portloclc. Geol. Report, pi. 2, fig. 8 (exclude the references), 1843. 



P. Murchisonii. Ibid., fig. 9. 



Var. 9 ? P. Dalmani. Ibid., fig. 7. 



P. Brongniarti and P. Dalmani, Salter, in Decade 7, Geol. Survey, Art. 1, p. 10, 



1853 ; and in Morris's Catalogue, second edition, pp. 112, 113, 



1854. 



S P. biuncialis, elougatus, gra/ndatus ; capite longo trigono, fronte angulato subrecurvo. 

 Glabella ad basin contractu, antice valde dilatata ncc convexa, lobis utrinauc tribus radi- 

 antibus ; lobo antico maximo triangulalo, a froutali sidco valido — a medio sulco leviore — 

 sejuncto ; lobis infimis minutis hamisp>hericis circumscriptis sese remotis. Oculi maximi, a 

 lobo froutali usque ad sulcurn cervicalem tracti. Anguli genarum obtusi. Thorax later ibus 

 parallelis, axi convexo angustato, pleuris abruplc de/lexis apicibusque rotundatis — -falcro 

 intra medium posito. Cauda trigona, axi longe conico angustissimo fere ad fmem caudce 

 extenso, 10-annulato ; lateribus 5-costatis, costis per totum divisis, nee margincm lavem 

 attingentibus. 



? or var. Dalmani, figs. 25, 26. 



Omnino precedenti simillimus, glabella, caudd, oculis — sed fronte capitis rolundato 

 nee producto. 



