24 SILURIAN TRILOBITES. 



and being quite obsolete in the lower. Only the upper ones are interlined. There is no 

 marginal flattened space, nor any concavity ; the tail is gently convex to the very edge. 



Locality. Wenlock Shale and Limestone. — Malvern, abundant in Wenlock Shale ; 

 Dudley. It has not yet been found in other localities. 



Subgenus — Acaste. 

 Phacops (A caste) Downinglx, March. PI. II, figs. 17 — 3fi. 



Calymene macrofhthalma, Brongniart. Crust. Foss., pi. i, fig. 4 {not fig. 5), 1822. 



— — BucMand. Bridgwater Treatise, pi. lxiv, fig. 5 {not fig. 



4), 1836. 



— Down ingle, Murchison. Silurian System, pi. xiv, fig. 3, 183". 



— — Milne-Edwards. Crust., iii, 324, 1840. 



Asaphus subcaudatus and A. Cawdori, Murchison. SiL System, pi. vii, figs. 9, 10. 

 Acaste Downingi^, Goldfuss. Syst. Uebersicht der Trilob., Neues Jahrb., 563, 1843. 

 Phacops macrophthalma, Burmeister. Organiz. der Trilob., 139, 140, 1843, ed. 2 



(Ray Society), 1846, p. 92. 



— Downingi,e, Emmerich. Neues Jahrb., 1845, p. 40, pi. i, fig. 2 {icon mala). 



— — Translated in Taylor's Scientific Memoirs, 1845, vol. iv, pi. iv, 



fig. 2. 



— — Salter. Memoirs Geol. Survey, June, 1848, vol. ii, pt. i, p. 336, 



pi. v, figs. 2 — 4 ; \Decade vii (1853), pi. i. 



— — M'Coy. Synopsis Pal. Foss. Wocdw. Mus., 160, 1851. 



— — Murchison. Siluria, 2nd edit., pi. 18, figs. 2 — 5, 1859. 



P.vix biuncialis, alutaceus, margini frontali capitis angulato. Glabella depressa sub- 

 parallela, sulcis utrinque tribus distinctis, lobo basali lineari, secundo ovali, superiori trans- 

 verso, sulco anlico ascendente sinuato ; lobis omnibus pi anis, fere ad medium glabella, spatio 

 angusto interjecto, extensis ; cervice elevato. Oculi modici. Cauda subtrigona, marginata, 

 apice angulato ; axi conveoco cosiato, costis 5 distinctis pradito ; lateribus o-costatis, costis 

 duplicatis. 



If I have given a lengthy set of synonyms, they do not represent a moiety of the works 

 in which this very common fossil is noticed. It is one of the really abundant Upper 

 Silurian species, being moreover one of the few trilobites which are common in the Ludlow 

 rocks, as well as in Wenlock strata. No trilobite is more frequent on the Dudley slabs ; 

 but it is rare to find it in the underlying shale. I have seen it from many parts of Britain, 

 but do not know that it has ever been described from foreign localities ; nevertheless it 

 does occur in the true Upper Ludlow rocks of Nova Scotia, as we learn from the collec- 

 tions brought to the International Exhibition by the Rev. D. Honeyman, in 1862. 



An inch and a half long ; general form long, ovate, broader in front, the axis following 

 the same lines, and regularly tapering towards the tail. The surface is moderately convex, 



