I916. No. 10. THE LOWER CAMBRIAN HOLMIA FAUNA. 33 



In front of the eyebrims we see a broad and distinct depression which 

 runs in a faint arc inwards to the apex of the glabella, and there joins 

 the dorsal furrows. In front of this depression, which on the whole has an 

 almost direct course straight across the cranidium, but by closer inspection 

 shows to proceede in three faint arcs, the margin becomes a prominent 

 broad frontal brim. The anterior margin of the cranidium ends in an 

 obtuse angle and the frontal brim thereby obtains a triangular outline : 

 here and there a fine marginal furrow. (PI. \'. fig. 4.) 



Cranidiums preserved in calcareous sandstone. 



We may assume that these cranidiums have to some degree preserved 

 their original plastic form. It is found that the shale specimens — as we 

 might expect — are considerabh" deformed by pressure. The fixed cheeks 

 and frontal brim in particular have suffered greatly, being pressed upwards 

 and thereby giving to the cranidium a different character to that which 

 it originally possessed. Comparing the illustrations, iPl. IV. fig. i — 3), we 

 notice in particular the instructive nature of the cross and longitudinal 

 sections. It is found that the fixed cheeks originally bent downwards in 

 a gentle arc, and that also the frontal brim must have been considerably 

 bent downwards, so that as seen from above they appeared comparatively 

 narrow, and did not convej- such a prominent appearance as those in the 

 usual state of preser\ation. The length of the cranidium is also thereby 

 shorter in proportion to the length of the glabella, 1 1 : 0.6 — 0.64 instead 

 of 1:0.42 — 0.51); but even in these cranidiums we see again the most 

 remarkable characters of t he shale specimens, particularly the markedly 

 arched glabella with well- defined lateral limitations, and the remarkable 

 furrows behind the frontal brims, which do not run parrallel to the anterior 

 margin, but somewhat obliquely towards the apex of the glabella. 



Comparing the descriptions thus given, it will be evident that this 

 important Lower Cambrian Stremtella species is characterised by a compara- 

 tively narrow, regularly conical glabella, which is rather markedly arched 

 in cross section and well limited towards the fixed cheeks. In the shale 

 specimens the latter are greatly compressed, so that the cranidium as a 

 whole appears to be flatter than usual, but in specimens plastically preserved 

 (in the calcareous sandstone bedsl they bends gently downwards. The frontal 

 brim in such specimens bends rather sharply downwards and is limited 

 posteriori}- bv distinct fijrrows or grooves, which cut almost direct towards 

 the front part of the glabella. In the shale specimens this frontal brim is 

 greath' pressed upwards so that as seen from above it increases conside- 

 rably in breadth and has a marked triangular boundary. 



Vid.-Selsk. Skrifter. I. M.-N. Kl. :qi6. No. 10. 3 



