44 JOHAN KIÆR. M.-N. Kl. 



the circumstance that the occipital ring is distinct, and even sharply marked, 

 and that the glabella has a more Strenuella- like character. The latter is 

 shown by the slight diminution in breadth towards the anterior, and by 

 the glabella being sometimes rounded and at others slightly pointed, and 

 provided with distinct furrows. Ellipsocephalus Nordenskjøldi thus represents 

 a complete transition form between the two genera. 



The Development and Relationship of the Ellipsocephalidae. 



In describing the Norwegian species and genera of Ellipsocephalidae, 

 I have several times had occasion to mention the phylogonetic development 

 that is clearly traceable within the family. I will now give a collective 

 account of these conditions. As mentioned in the foregoing pages, the 

 Scandinavian Lower Cambrian contains a number of closely related forms, 

 some of which evidently belong to the genus Strenuella Matthew, whilst 

 others constitute a distinct transition to Ellipsocephalus Zknker and have 

 in consequence been referred to that genus. The difference between these 

 genera, however, is slight in the Lower Cambrian, a fact that will be best 

 seen by a study of the figures in plates 1\' — V. Of these two genera, 

 Strenuella Matthew is the most original, and we may therefore first consider 

 that more closely. 



The genus appears in the upper part of the Lower Cambrian in 

 Scandinavia, and in the easterl}- part of N. America, in both regions almost 

 contemporaneously. In Scandinavia it belongs to the Holmia fauna, in the 

 Atlantic provinces of N. America to the Callavia fauna. It is possible that 

 it occurs in the Pacific regions in still older beds ^. 



In both of the above mentioned regions Strenuella forms appear to be 

 the most common and the most characteristic fossils, and have thus played 

 a prominent part in the faunae in question which belong to the upper part 

 of the Lower Cambrian. From America we know the type forms Str. 

 strenua Billings with var. nasuta Walcott-. From Scandinavia we have 

 Str. primaeva Brøgger, and the very closely related species — or rather 

 varieties — baltica Wiman and rotundata (nov. nom.), and also Str. Linnars- 

 soni nov. sp. 



' In Walcott's work „Cambrian Sections of the Cordilleran Area" (Smiths Misc. Coll. Vol, 

 LIII, No. 5, 1908) several Agraiilos are mentioned from Lower Cambrian. These 

 forms are still undescribed, and it is therefore not possible to decide whether they 

 are Strenuella or typical Agraulos forms. They presumably belong to the former genus 

 which is mainly Lower Cambrian. 



- This form, which Matthew gives as Strenuella (?) Halliana, does not appear to be 

 referable to that genus, but to Agraulos. (The fauna of St. John Group, No. IV, Trans. 

 Roy. Soc, Canada, Vol. V. 1887, Page 132.) 



