660 



TRILOBITES OF THE LOWER SILURIAN ROCKS. 



Trinucleus fimbriatus (n.s.), f» 2. 



Marginal pores in diverging rows in the front of the shield; on the sides scattered ; lateral 

 spike of the buckler divergent from the body. Caudal ribs 12 on each side. 



This is probably the same species figured by Lhwyd, Epist. I. p. 9. t. 23. I have never found 

 it entire, but the caudal extremity occurring in the same fragment of rock with the buckler, and 

 both agreeing with the figure of Lhwyd, I have considered them as parts of the same species. 

 The simple fimbriated rim of the buckler distinguishes this species from the others 1 , 

 Loc. Near Welsh Pool and Builth. 

 Trinucleus radiatus (n.s.), figs. 3 a and b. 



Marginal pores arranged on the front of the head in 1 or 2 rows; on the sides in long ra~ 

 diating lines. Buckler square, lateral spikes short. 



Although fragments of the head only have been found, there ean be no hesitation in re- 

 ferring them to the genus Trinucleus, while the radiating lines and general outline of the 

 buckler are very distinct from those of any other species. 

 Loc. Trilobit e Dingle, Welsh Pool ; Caradoc and Meifod Hills, fyc. 

 Trinucleus Lloydii (n.s.), f. 4. 



Marginal pores on the front of the head in several rows; on the sides scattered. Buckler 

 round } with lateral spikes advancing beyond the body, ivhich is composed of 5 ribs. 



Caudal portion semicircular. Tail obtuse, ribs on each side terminating in hooked points. 



This species is at once distinguished from other Trinuclei by the vast length of the buckler, 

 which with the pendent cheeks advancing to the posterior extremity of the animal, constitute 

 a peculiarity not observed in any other published trilobite. 



Loc. This beautiful and rare species was found in the black flag of Blaen-dyffrin-garn, near 

 Llangadock, by the Rev. Henry Lloyd of Tan-yr-alt. The rock is one of the superior beds 

 of the Lower Silurian Rocks, and owes its hard character to the boss of trap by which it is 

 thrown off. 

 Trinucleus nudus (n.s.), f. 5. 



Three nuclei of the head without the ornamented buckler. It differs from T. fimbriatus in 



the number of caudal ribs, (9 or 10 instead of 12,) and in the outline of the head which is more 



oval. 



Loc. Gwern-y-fad, near Builth in Llandeilo Flags; the Gilwern Hills, near LlandrindocL 

 Trinucleus f Asaphoides (n,s.), f. 6. 



Three nuclei less distinct than in the other species, and general form approaching to that of 

 Asaphus ; hence its name. 



Though distorted, this little specimen is interesting, in showing the passage from the 

 Trinucleus to the Asaphus, the leading distinction of a sculptured shield being scarcely per- 

 ceptible. 



Loc. Near Builth. 



Judging from these specimens, I should infer that they belonged on the whole to the Lower Silurian Rocks. 

 The Graptolite and the Orthoceratite, figured PI. 3., are probably from the lowest beds of the Upper Silurian 

 Rocks. 



1 Brongniart has figured fragments of this genus, from drawings of Mr. Stokes, PI. 4. figs. 5, 6 and 7., but 

 assigns no name to them, referring them with doubt to Asaphus cornigerus, from which, however, they are 

 distinct. 



