68 JOHAN KIÆR. M.-N. Kl. 



present writer in a weathered sandy limestone from the Hobnia shales at 

 Tomten. A similar but less complete specimen came from Kletten (Collec- 

 tor W. C. Brøgger). This stage will be seen somewhat restored in the 

 text-figure lib, where a number of successive stages of development are 

 illustrated. The length of the cranidium is 3 mm. 



The clearly segmented axis is here somewhat broader. The palpebral 

 ribs have become shorter and stand out as distinct ocular ribs. The segmen- 

 tation on the cheeks has disappeared and the intergenal ribs have become 

 weaker, being more like those of the adult specimens. The whole cranidium 

 is still surrounded by a broad, flat brim; the genal spines cannot be defined 

 but were probably short. 



This specimen evidenth' represents a earl}' nepionic stage; we 

 may imagine that a smaller number of thoracic segments were already 

 developed. 



The little cranidium depicted in pi. VIII, fig. 3, is somewhat further 

 developed. This also came from the weathered sandy limestone from Tomten. 



A good step forwards in development is represented by the little 

 cranidium from Kletten (Collector W. C Brogger), in pi. VI, fig. 3. The 

 length of the cranidium is 3.7 mm. The frontal lobe is distinctly enlarged 

 and elongated, and extends forwards towards the anterior margin, but the 

 glabella is still quite narrow and of even breadth. The eyes in this stage 

 have become shorter and the posterior margin swings forwards towards 

 the genal spines in the arc that is characteristic of Hobnia. The broad 

 brim round the cranidium has altered and the cranidium in its form and 

 structure has already obtained more of the peculiarities that distinguish the 

 genus. Presumably all the thoracic segments have already been developed, 

 so that we have here a early neanic stage. 



A late neanic stage is represented by the cranidium depicted in pi. 

 \\, fig. 4. The length is 4.5 mm. The Hobnia Kjerulfi form is here some- 

 what further developed, but the glabella is still more uniformly broad than 

 in the case of adult specimens, and the outline of the cranidium is more 

 broadly rounded, which is also the case in the cranidium, (9 mm. long), 

 in pi. VI, fig. 5. The eyes are longer than in the early neanic stages. 



Cranidia of 10 mm. length and upwards have most of the charac- 

 ters of Hobnia Kjcndfi fully developed, and may therefore best be regarded 

 as ephebic stages. However, these glabellae also increase in breadth and 

 extent forwards with increasing size, a factor that will be made evident by 

 a study of the cranidia depicted in pi. \'I, figs 6 — 11. 



The thoracic segments, too, are narrower in 3'ounger specimens than 

 in older ones; we may compare the reconstructions in the text-figures 8 



