from Millstone Grit, N. Yorkshire. 393 



surrounding border is broad, and ornamented by fine ribs, wbicb run 

 parallel to the margin. The cheeks are produced posteriorly to form 

 conspicuous flattened spines, which reach to the sixth thoracic 

 segment. 



The eyes are three-tenths the length of the glabella; they are 

 finely facetted and reniform. 



Most of the specimens, when the original shell is preserved, show 

 two depressions, one on either side of the glabella, above the eye-lobe. 



Thorax consists of nine segments. The axis is slightly tapering, 

 and is rather less than one-third of the total width of the thorax. It 

 is ornamented with a single row of fine granules along the posterior 

 border. The pleurae are grooved and end rather squarelj", although 

 the anterior angle is slightly rounded, and the posterior angle is 

 produced to form a very short blunt spine. 



Pygidium semi-ovate in outline. Central axis elevated and 

 tapering, but ending bluntly. It is composed of sixteen fused 

 segments. The lateral lobes are ten in number. The axis is 

 ornamented in the same manner as the thoracic axis. The lateral 

 lobes are smooth. The pygidium is completely surrounded by a 

 broad, slightly curved border, the margin is entire. 



Hypostome similar to that of Phillipsia Eichivaldi,^ length 

 two-thirds that of tlie glabella. Upper border curved anteriorly. 

 The oblong raised central portion is parallel-sided, and ornamented by 

 small pits. There are two posteriorly directed oblique furrows on 

 tlie lower parts of this raised portion. The wings are broadest in the 

 iipper portions, where their breadth is equal to the total length. 

 Prom the place of greatest breadth they narrow lapidly towards the 

 centre of the hypostome and then follow the raised axis ; their lower 

 portion is well developed, and ends bluntly with rounded angles. 

 The surface of the wings is finely ridged; these ridges are specially 

 well-develo[)ed in the broader parts. (See Plate XXXII, Fig. 3.) 



This species, although in many respects similar to Phillipsia 

 Eichwaldi (Pischer), differs from it, firstly, in having no well-marked 

 glabella furrows ; secondly, the lobe over the eye is much more 

 developed in the Shunner Pell species; and thirdly, the pygidium is 

 of a slightly different outline. 



The only species of Griffithides with genal spines of similar 

 proportions is G. longispiniis (Portl.). The whole shape of this 

 species is quite different. G. acanthiceps (H. Woodward) is of similar 

 appearance, but its pygidium has only thirteen segments. The 

 figures of G. calcaratus (McCoy) are not good enough to identity 

 a specimen from; moreover, its glabella is said to be smooth. 



Many theories have been advanced as to the use of the ' pores ' on 

 the glabella of Trilobites. The subject is discussed by Dr. AVoodward 

 in an appendix to his work on the Carboniferous Trilobites in the 

 Memoirs of the Palaeontographical Society.* 



The following are among the suggestions which have been put 

 forward : that they were points of attachment of external antennae ; 



^ H. Woodward, Carboniferous Trilobites (Palaeont. See), pi. iv, fig. 4. 

 '^ Ibid., 1884, pp. 71-6. 



