CHEIRURUS. G7 



as wide as the pleurae. The most important variations occur in the tail. In figs. 10, 15, 

 we have represented the spines as all directed backwards, and the two central ones closely 

 approximate; they are so in the large Ledbury specimen figured in the ' Silurian System,' 

 where, too, they are shorter than the outer spines. In others they are a little space apart. 

 In a Lower Silurian specimen we have seen a small tubercle appear between, and in our 

 var. /3, figs. 9, 18, a decided, though short, mucro protrudes. Lastly, as a monstrous variety 

 from the Silurian rocks of Kildare (we have reason to think it of the same species), we have 

 one with a wider interval and a bifid mucro. In old specimens, as well as in var. 0, the spines 

 diverge much more than in most of those here figured. Perhaps some of these variations 

 are due to sex. It is observable in some specimens (fig. 9) that a double row of tubercles, 

 like those observed in Phacops (p. 52), occurs down the axis of the thorax. 



Affinities. — Among a host of kindred species in this prolific genus, the only Bohemian 

 fossil with which it is really necessary to compare this is the C. insignis, Beyrieh. 

 Barrande's figures leave nothing to desire, and I confess I know not how to separate the 

 two. C. insignis has a somewhat different habit, and the central tail-spine is more 

 prominently developed. But except this, and having a less overhanging glabella, I do not 

 know how to distinguish the Bohemian form, nor can my friend Mr. H. Woodward see 

 any differences of value. 



With the C. speciosus, as figured by Hisinger, I believe ours to be identical. C/i. 

 (Calgmene) ornatus of Dalman has the head very like, as we learn from Angelin's figure ; 

 but the upper glabella-lobe of that species is not nearly so long as ours, nor is it wide 

 enough above. The British species is variable enough ; but it is, for all that, distinct from 

 those above quoted. 



Localities. — Caradoc to Ludlow Rocks ; Caradoc, South Wales, near Haverfordwest, 

 abundant ; North Wales j Kildare, Ireland. Llandovery Rocks of Goleugoed, near Llan- 

 dovery, South Wales ; Mullock, Ayrshire ; Galway, &c. May Hill Sandstone, Nor- 

 bury ; (PI. V, fig. 3). Also in the purple Shales, Onny River, Shropshire. Woolhope 

 Limestone, Presteign ; Malvern. Wenlock Limestone and Shale, everywhere. Wenlock 

 strata of South Wales, and West of Ireland. Aymestry Limestone, Downton Castle, 

 Ludlow. Also in Sweden and Bohemia (Upper Silurian). 



Ch. (actinopeltis) juvenis, Salter. PI. V, figs. 9 — 12. 



Cheirurus juvenis, Salter. Memoirs Geol. Survey, vol. ii, pt. 1, pi. vii, figs. 1 — 3, 

 (exclude 3, b, which belongs to the next species), 1853. 



— clavifrons, Id. Ibid., Errata, p. viii. 



— — Id., in Appendix Synops. Paleeoz. Fossils of Woodw. Mus., 



t. iF, fig. 11 ; t. iG, fig. 9, 1851. 

 Ceraurus clavifrons, M'Coij. Ibid., p. 154 (but not t. 1 f, fig. 12, for which see 



Sphcerexochus boops). 



This rather common fossil has been bandied about, in search of a godfather, for some 



