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1 6. Xo. I o. THE LOWER CAMBRIAN HOLMIA FAUNA. 



page 78) ^ It is flat with a faintl}- arched axis and faintly raised palpe- 

 bral lobes. This faint arching must be considered as being the result of 

 pressure in the shales, and the cranidium may therefore be assumed to have 

 been more arched in its original state At the sides, the broad marginal 

 brim appears faintly arched, and as a rule distinctly defined. Just outside 

 the eye it occupies about - 3 of the breadth between the outer margin 

 and the eye, and as a rule grows narrower forwards. Posteriorly it 

 passes into the broad, comparatively short genal spines, which have sharp 

 points which bend somewhat outwards. The frontal margin is faintly 

 projecting. 



The posterior margin extends almost straight outwards towards the 

 genal spines, but in well preserved specimens we observe a slightly promi- 

 nent intergenal angle, almost half-way between the side furrows of the 

 occipital segment and the outer margin. From the occipital segment the 

 posterior margin therefore proceeds slightly backwards to this genal angle 

 before it again runs more direct outwardly towards the curve of the genal 

 spine. 



The Glabella is very broad and flat. Its greatest breadth is greater 

 than half the length of the head. It is of somewhat even breadth. The 

 frontal lobe is almost of the same breadth as lengdi and generally narrows 

 greatly anteriorly. As a rule it is pear-shaped or triangular. In well 

 preserved specimens the glabella extends so far forwards that all that 

 remains is a narrow brim in front of it. 



The second lobe is narrow, but extends somewhat farther out to 

 the side than the first, and forms the broadest part of the glabella. It bends 

 faintly backwards in its outer part, but is not geniculated. 



The third lobe again is broader than the second but does not 

 extend so far out to the sides, and is evenly rounded in its outer part. 

 The fourth lobe is still broader but in its outer part is usually faintly 

 defined. The fifth lobe (occipital segmenti is somewhat narrower than the 

 4th and at the side in its posterior region shows a faint bifurcation, extending 

 laterally almost like the two foregoing lobes. Behind it has a quite faint 

 and bud-shaped occipital spine. 



The furrows between the lobes are clearly developed, and the fore- 

 most especially slightly reflected. The first two apparently run straight 

 across the glabella, but however fall oft' somewhat at the centre, (particu- 



' In greatly compressed and grown specimens this condition maj- vary within %vide 

 limits, either the breadth or the length being disproportionately great. iSee fig. i — 2, 

 pi. Xi. 



