50 TRILOBITES OF GIRVAN. 



liead-sliield ; anterior end gently convex ; sides concave. Frontal lobe large, 

 transverse, subrhomboidal, slightly overhanging at sides, about half the lengtli of 

 the glabella. Three pairs of lateral lobes present ; anterior lateral lobe triangular, 

 not circumscribed, about one-fourth the length of glabella along axial furroAV and 

 equal in lengtli to the two posterior lobes together ; middle and basal lateral lobes 

 oblong, transverse, of equal size, nearly parallel-sided, but basal lobes wi*"h outer 

 portion rather swollen and subnodular. 



First lateral furrows slightly sinuous, directed rather obliquely backwards and 

 inwards, and making an angle of about 45° with axial furrows, arising at about 

 three-fifths the length of the glabella from base and extending inwards about one- 

 third its width, not joining second lateral furrows. 



Second lateral furrows arising from axial furrows nearly at right angles al)out 

 halfway between first lateral and occipital furrows, nearly straight, obliqueh" 

 directed forwards and inwards, extending fully one-third across glabella. 



Third lateral furrows equal in length and parallel to second pair, situated 

 about half way between them and occipital furrow. Occipital furrow strong, con- 

 tinuous, arched forwards in middle. Meso-occipital ring with lateral portions 

 narrower and swollen into small, low, rounded nodes. 



Axial furrows moderately strong, curved inwards, concave outwards, strongly 

 divergent in front of second lateral lobes. Fixed cheeks with inner portion swollen, 

 rising higher than glabella and sloping up to eye-lobe ; posterior wing very narrow 

 behind eye, widening laterally and arched down to genal angle. Pleuro-occipital 

 segment widening laterally, marked off by strong sigmoidal neck-furrow, bending 

 back to genal angle outside eye. Lateral border increasing slightly in width 

 posteriorly, Avitli shallow marginal furrow meeting pleuro-occipital furrow at 

 about 60°. Genal angle produced back into flattened stout spine extending to 

 fourth or fifth thoracic segment. 



Eye-lobes small, subacute, swollen, upturned, with smooth almost vertical 

 broad outer band separated off by strong angulated furrow and closely pressed 

 against inner surface of eye. 



Facial sutures with posterior branch sigmoidally arched forwards behind eye to 

 cut lateral margin of head-shield a little in front of base of eye. 



Free cheeks small, triangular, sloping steeply upwards from margin to base of 

 eye ; border gently convex, separated off by well-marked marginal furrow. 



Eyes parallel to axis, large, very high and prominent, conical, semilunar in 

 shape, strongly curved, less than half the lengtli of glabella, with anterior end 

 touching axial furrow at first lateral furrow of glabella, and with posterior end 

 opposite third lateral furrow and distant from side of glabella about one-third its 

 basal width. Lens-bearing surface of eye very tall, almost perpendicular to 

 general plane of head, possessing 14 or 15 lenses in middle vertical rows and about 

 100 lenses in all. Surface of glabella, especially frontal lobe, ornamented with 



