34 CARBONIFEROUS TRILOBITES. 



composed of thirteen coalesced somites, ornamented in a similar manner to the 

 free thoracic ones ; axis tapering to a blunt extremity, and surrounded at its termi- 

 nation by the smooth border of the tail-shield ; ribs nine in number, dying out 

 near the margin. 



Formation. — Carboniferous Limestone. 



Localities. — Settle, Yorkshire ; Cookstown, Tyrone ; Creggane, Limerick ; 

 Brockley, near Lesmahagow. 



The following is Portlock's original description of his Griffithides longiceps -} 



" Glabella elevated, rounded, and swollen in front, but narrowing gradually 

 towards the base, the external surface covered with minute dots, and, when 

 removed, the surface below appears rather granular or rugose ; length rather more 

 than four tenths of an inch, breadth in front three tenths, and at the base three 

 twentieths ; eye-projection, very small, and near the base. Thorax imperfect, but 

 showing the lateral segments to be compound. Pygidium, in length four tenths, 

 breadth five tenths of an inch ; axal lobe elevated ; segments thirteen, with about 

 twelve granules or small tubercles on each, and a rounded extremity also covered 

 with granules ; lateral segments about nine on each side, with a row of small 

 tubercles on each, not quite extending to the margin, which is flattened or turned 

 up, and strongly striated on the edge and under surface. The prolongation of the 

 segments is marked by slight elevations on the margin ; the flattened and turned-up 

 margin of the pygidia of this genus is generally more striking than in Philllpsla, 

 in which the pygidial margin follows the slope of the lateral segments, but the 

 character depends in part upon the condition of the crust, being more marked 

 when it is decorticated.'' 



In Prof. Morris's ' Catalogue of British Fossils,' p. 109, and also in H. Wood- 

 ward's ' Catalogue of British Fossil Crustacea,' p. 37, Portlock's Griffithides longi- 

 spinus (' Geol. Rep.,' Lond., p. 312, pi. xxiv, fig. 12) is made a synonym of 

 Griffithides longiceps, Portl. A careful examination of Portlock's type specimen, 

 kindly lent to me by the authorities of the Museum of Practical Geology, Jermyn 

 Street, enables me to state that it is quite distinct from G. longiceps, and I 

 figure it, with others, on PI. VII, figs. 5 and 6. 



12. GiiiFFiTiiiDEs PLATYCEPS, Vortlock, 1843. PI. VI, fig. 13. 



Geiffithides flattceps, Portlock. Eep. Geol. Lond., p. 311, pi. xi, fig. 8, 1813. 



— — Morris. Cat. Brit. Foss., p. 109, 1854. 



— — JS. Woodw. Cat. Brit. Foss. Crust., p. 37, 1877. 



1 ' Geology of Londonderry ' (1843), p. 310. 



