Vol. 67.] ASSOCIATED ROCKS OF NORTH-EAST MONTGOMERYSHIRE. 449 



IX. Notes on the Paleontology or the Area. 

 (1) Trilobita. 



Trinucleus intermedius, sp. nov. (PI. XXXVI, figs. 1 & 2.) 



Trinucleus concentricus Hall, ' Palaeontology of New York ' vol. i (1847) p. 249 

 & pi. lxv, figs. 4 a-4 c ; also p. 255 & pi. lxvii, figs. 1 a-1 h. 



Length = 18 mm. ; width = 21 mm. General form almost circular. 

 Head-shield semicircular, widest across the junction with the body- 

 segments. 



Fringe flat or concave in front, sloping downwards at about 60° 

 at the genal angles, where it is produced backwards into long ears 

 which reach to the tail. Spines straight and parallel, continued 

 beyond the tail to a distance equal to the length of the main part 

 of the test. Glabella pyriform and swollen, not equal in width to 

 the cheeks, encroaching slightly in front on the fringe, posteriorly 

 carinate. Base of the glabella narrow, with an obscure neck-furrow, 

 which is continued along the posterior edge of the cheeks, where it 

 bends abruptly at the margin of the ears. Cheeks swollen and 

 wide, quite smooth. In the anterior part of the fringe are five 

 rows of pits, the three posterior rows being of equal size, the two 

 outer rows smaller. The three inner rows are concentric and radial ; 

 in the outer two rows the pits are smaller and more numerous, and 

 therefore some of them take positions intermediate to the radii of 

 the inner rows. The two innermost rows are separated from the 

 others on the lower surface of the fringe by a ridge which runs 

 round to the genal angles. At the genal angles, and in the space 

 between the front of the glabella and the cheeks, the number of pits 

 increases : in the former case to seven rows, in the latter case to 

 six. The fringe has a thick flattened rim or edge along its outer 

 margin. 



The body is equal in length to the tail, but both together are 

 only two-thirds of the length of the glabella and fringe. The body 

 consists of five or six flat joints, the axis alone being convex. The 

 first three joints are overlapped at their margins by the ears of the 

 fringe. The axis is narrow, about a sixth of the width of the 

 thorax. Pleurae narrow, horizontal and flat, but curving slightly 

 backwards at their outer extremities. They are grooved with a 

 furrow which is almost parallel with the edges of the pleurae. 

 Pygidium subtriangular and flat ; anterior margin slightly rounded 

 and thickened. Axis conical and elevated ; markings of rings and 

 furrows on tail very obscure. 



Remarks. — This remarkable species is readily distinguished from 

 Trinucleus concentricus l by the large pendent ears of the fringe 

 and the direct backward extension of the spines. The front of 

 the fringe is more evenly semicircular than in Tr. concentricus, 



1 J. W. Salter, Q. J. G. S. vol. iii (1847) pp. 251 et seqq. [The Trinucleus 

 ornatus there described is now recognized as Tr. concentricus.] 



