1916. No. 10. THE LOWER CAMBRIAN HOLMIA FALNA. 63 



The H y p o s t o m e Attachments are comparatively broad posteriorly, 

 diminish somewhat in breadth, and with the doublure correspond to the 

 marginal rim of the upper side. 



The Thoracic Segments are i6 in number; the axis narrows regu- 

 larly posteriorly, and is bounded by somewat marked dorsal furrows. 

 In the posterior edge of the dorsal furrow we see a marked incision, from 

 which there proceeds a faintly marked furrow inwards and slightly forwards. 

 The rachis of the segments is thereby like the occipital segment and gives an 

 impression of being slightly bifurcated. The foremost parts of the ring extend 

 somewhat farther out to the side than is the case with those behind. The 

 pleurae are narrow; the foremost ones go straight outwards, and then 

 proceed argularlv in somewhat straight deflected pleural spines of about 

 the same length as the inner straight portion of the pleurae. The latter 

 is provided with a distinctly marked oblique furrow. From the loth seg- 

 ment the pleurae become more bent and finally almost sickle shaped; the 

 last bends almost straight backwards round the little pygidium. 



Like the occipital segment the thoracic segments are provided with 

 pow erfüll thoracic spines, which at first are somewhat weaker than 

 these of the occipital segment, but by degrees increase in length, particularly 

 in the case of the loth segment. The loth to the 14th segments are armed 

 with long and powerful spines, which like the foregoing bend backwards. 

 The spine on the 13th segment is the longest and extends almost to the 

 posterior edge of the pygidium. 



The 15th — i6th segments are unarmed, but now and then we see a 

 small bud-shaped spine on the 15th segment. 



The Pygidium is very small, patch-shaped, with the posterior margin 

 cut oft' somewhat straight. The length is about ^ s of the length of the 

 cranidium; the breadth is somewhat greater than the length. It is mainly 

 comprised by the short axis which is rounded posteriorly, showing a faint 

 bipartition or tripartition. The axis is surrounded by a narrow margin 

 that is bent downwards, and is especially distinct near the posterior genal 

 angles. 



Sculpture: The shell as a rule appears quite smooth, but in some 

 cases there is a fine reticulated sculpture apparent. iPl. XI\', fig. 3.» 



Dimensions: Holinia Kjcntlfi Lnrs. as a rule does not attain to 

 an}" considerable dimensions. Most commonh' the cranidium is some 15 — 

 21 mm. in length, which corresponds to a length of the body of 36 — 55 mm. 

 1 refer to PI. \'I and \'III, which show the cranidiums and complete speci- 

 mens of this form in natural size. There are however, a number of crani- 

 dia of greater dimensions, up to 30 mm. in length and 54 mm. in 



