ßö JOHAN KIÆR. M.-N. Kl. 



demonstrating a remarkable articulation apparatus that is not found in other 

 Cambrian trilobites. and by reason of which the segments evidently have 

 greater chances of remaining united even when the connecting membrane 

 has disappeared. In the case of Ellipsocephalidae there is presumably no such 

 condition, and the separate segments at last are parted from each other by 

 the slightest movement of the water. 



Occurrence. Cranidiums of this form are extremely common in 

 the Holmia shales at Temten, and a large amount of material is present. 

 Also found in a piece of sandy limestone from the same locality. 



Observations. Having now determined the typical Strenuella primaeva 

 Bkøgger as exactly as the material available permits, we may now proceed 

 to compare it with other forms. 



Arionellus primaeviis Brøgger, which I here refer to the genus Strenu- 

 ella, is mentioned from several Swedish localities. Thus Linnarsson 

 described it in his work »De undre Paradoxideslagren vid Andrarum« ^ 

 He there givens as quite a typical specimen a little cranidium — only 5 mm. 

 long — from the mica sandstone at Forsemella (PI. IV, fig. 3). Presumably 

 we have here the same form as that from Temten, although the glabella 

 to judge from the enlarged figure is somewhat longer and broader than 

 in any of the Norwegian specimens measured. Fig 4 represents the larger 

 form of which several specimens were found in the usual coarse shales in 

 the same locality, and which was also found at Gislöf. The dimensions of 

 the cranidium considerably exceed those of all the specimens in my material ; 

 yet although its remarkable breadth — as pointed out by Linnarsson — 

 •appears to agree with the characteristics that according to Barrande's 

 description appear to distinguish old specimens of Agi'aidos ceticephalus 

 Bar., it seems to be most reasonable to regard them in the same way as 

 the former. Linnarsson therefore united them — at least provisionally — 

 with primaevus Brøgger, with which the proportions of the cranidium 

 closely agree. The form of the glabella, however, by its more rounded 

 and pointed contours differs from that all of my specimens, and to such 

 a degree that it is probably better to place it as a separate variety or 

 closely related species until a real transition form has been discovered. 



In »Studien über das nordbaltische Silurgebiet« i,^ C. Wiman described 

 an Stremiella form from a loose block of bituminous Olenellus sandstone, 

 which he calls balticus. It is a very large and flat form, with a length 

 of cranidium approaching 19.5 mm. It appears to be very near primaeva, 

 nearer in fact than Wiman believed. He states that it differs from tho 



^ Bull, of the Geol. Inst, of Uppsala, Vol. VI, 1902. 



