TRILOBITES OF THE LOWER SILURIAN ROCKS. 



659 



The raised and beaded, if not toothed rim of the buckler is also curious, and may serve to 

 distinguish this from any species of the genus Acidaspis which may hereafter be found. I de- 

 dicate it with much pleasure to Mr. B. Bright, to whom the original belongs, and the liberal 

 use of whose rich cabinet has assisted me so materially to illustrate this work. 

 Loc. TVenlock Limestone of the Malvern Hills, 



TRILOBITES OF THE LOWER SILURIAN ROCKS (CARADOC AND LLANDEILO 



FORMATIONS). 



Tri nucleus, PL 23. figs. 1 to 6. (Lhwyd Ichnogr. Lith. Brit. Epist. t. 23.) Crypto lithus, 

 Green. Asaphus granulatus ?, Dalm. 



Gen. Char. (Nobis.) — Caput obtusum, scutum marginem versus punctulis concavis ex ordine 

 collocatis ornatum, trilobum : lobis rotundato-protuberantibus, medio lateralibus minore. 

 Corpus breve, 5 — 7 costatum : costis lateralibus rectis. 

 Pygidium trilobatum breve. 



Seeing that these distinctions, as above defined, prevail in several species of trilobites, I have 

 formed them into a new genus under an old name assigned to one species of an animal of this 

 form by Lhwyd . 

 Trinucleus Caractaci (n.s.), figs. 1 a, b, c, d, e and/. 



Spec. Char. — Marginal pores of the shield in concentric rows (5 and 6) in the front, on the sides 

 scattered and terminated laterally by a plain, slender, pointed cheek or spike, which extends 

 beyond the body. Caudal furrows, 5 on each side. Tail obtusely mucronated. 



The marginal pores magnified, are seen (in f. 1.) to penetrate the shield, a peculiarity so 

 great in crustaceans, that if Lhwyd had not originally figured one of this genus as Trinucleus, 

 and Green had not subsequently called it Cryptolithus, I might, as before stated, p. 217, have 

 proposed the generic name of Tretaspis (perforated or deeply sculptured shell). The lateral 

 spike of the buckler is found in well-preserved specimens only, or those which have been de- 

 posited in finely levigated materials, figs. 1 c and 1 e. (Our species is quite distinct from the 

 Cryptolithus tessellatus (Green) of N. America in having 5 or 6, instead of 3, rows of marginal 

 sculpture on the shield, and also by the lateral spikes of the buckler.) 



Loc. This fossil is so abundant in the Caradoc formation that I have named it Trinucleus Ca- 

 ractaci. The specimens figured, as well as those of figs. 2 and 3, were collected by myself 

 in reddish and blackish, sandy shale, in a little dingle west of Welch Pool Church. The 

 same species, however, abounds in the impure limestone and sandstone on the eastern flanks 

 of the Caradoc Hills, in the Meifod Hills, Montgomeryshire, and occasionally, though rarely, 

 in the upper beds of the Llandeilo flags (Caermarthenshire) . It has also been found 

 with other Silurian fossils in Ireland (eastern part of Tyrone) and has very recently been 

 figured to illustrate a description of the structure of that region by Capt. Portlock, JUS. 

 (See Ordnance Survey of Ireland, vol. viii. PI. 1, 2 and 3 1 .) 



1 The figs. 6. PI. 1. and f. 8. PI. 2. of Capt. Portlock are the forms I should refer to my species Trinucleus 

 Caractaci, though not with absolute certainty, seeing that the specimens are mutilated. I may add, that 

 among these Irish specimens, f. 9. PI. 2., resembles the Illanus? Corndensis, PL 23. f. 7., while f. 7. PI. 2. o. 

 the Ordnance Survey is not unlike the Calymene? punctata PL 23. f. 8., though the former has no punctures. 



