CHEIRURUS. 71 



Comparing the side-view fig. 13, a, with the side-view fig. 11 of the nearly allied 

 species, C.juvenis, we at once see that it is distinct, and at the same time how very closely 

 these species of Actinopeltis approach each other. The glabella of C.juvenis is oval, not 

 oblong, and the free cheek less triangular, and a good deal larger, judging from the much 

 smaller fixed cheek left behind. The eyes, too, are placed far more backward, and the 

 neck-segment is more prominent. And if I am right, as I believe, in referring the tail 

 (fig. 12) to that species, there is, of course, no need to compare them minutely. 



Cgrt. affinis of Angelin is very like ours ; I think.it can only be a synonym. 



Localities. — Greenish Caradoc Sandstone of Pinwhapple, Ayrshire (Brit. Mus.) ; 

 Rhivvlas, Bala, and Cerrig-y-Druidion, Denbighshire (Mus. P. Geology). 



Ch. (Cheirurus) gelasinosus, Portlock. PI. V, figs. 6 — 8. 



Amphion gelasinosus, Portlock. Geo]. Rep., t. iii, fig. 4, 1843. 

 Arges planospinosus, Id. Ibid., t. v, fig. 9. 



Cheieurus gelasinosus, Beyrich. Bohm. Tril., i, p. 19, 1845. 



— planispinosus, Bronn. Ind. Pal., 1848. 



— gelasinosus, Salter. Quart. Geol. Journal, vol. vii, pi. viii, fig. 1, 1851. 



Decade 7 Geol. Survey, art. 2, p. 11, 1853. Siluria, 2nd 

 ed., p. 538, 1859. 



Ch. (Cheirurus) depressus, 3-uncialis. Caput transversum, glabella reclangulari, sulcis 

 brevibus transversis, lobo frontali brevi, basalibus oblongis transversis vix circumscriptis, 

 uno ab altera spatio cequali sejunctis ; genis lutis, marginibus aepres&is, spinis brevibus. 

 Cauda (hie haud dubie referta) lata, segmentis utrinque tribus latis, ad basin longe adnatis, 

 acuminatis ; primo in appendicem Ion gam producto, secundum longe excedente, hoc tertium 

 brevem superante ; axe 4-annulafo, articulo ultimo minimo angusto, nee apicem cauda 

 prqfunde emarginatum attingente. 



The specimens figured by General Portlock 1 no doubt belong to one and the same 

 species ; and the form has been recognized by both Beyrich, Barrande, and myself, as a 

 Cheirurus. It is rather a remarkable one, for the extreme width and shortness of the 

 head ; but the tail is of the ordinary form for the genus. 



We have specimens of the head nearly two inches wide ; the whole length may have 

 been three and a half inches, of which the short, wide head measures only ten lines. The 

 glabella is not so wide as the cheeks, and is rectangular-oblong,- with the upper angles 

 slightly rounded, and the sides strictly parallel. The furrows equal in length, rather 

 long, oblique, and but little curved downward, the basal ones complete, and enclosing 

 triangular oblong lobes, separated from each other by a space equal to their own diameter. 



1 While these pages are printing, we have to record the loss, at an advanced age, of this distinguished 

 man. His work in various departments will endure long, for it was done well. 



