I916. No. 10. THE LOWER CAMBRIAN HCLMIA FAUNA. 57 



I therefore consider Holiiiia Rowci Walcott as an old branch of ihe 

 Mcsoiiacidar, that has difterentiated from the oldest part of the Lower 

 Cambrian in a similar direction to that of the later Holmia group, without, 

 however, being genetically united with it. 



Hohiiia maccr Walcott is given by Walcott himself as a doubtiul 

 Holmia form. Nor is it completeh' known, the hindmost thoracic segments 

 and the pvgidium being lacking. The intergenal spines are also lacking 

 and the cranidium appears to difter in structure to that of Holmia K/rmlfi 

 Lnrs., especially with respect to the insertion of the hypostome in the 

 h\'postome attachments. The sole points of resemblance are the form of 

 the pleurae, and a certain resemblance between the actual shape of the 

 body. However, it appears to me also to be probable that this is no: a 

 genuine Holmia species. 



There is, however, another Scandinavian form, that exhibits closer 

 resemblance, viz. that onginall}' described by Moberg as Schmidtia? Torclli, 

 from Björkelunda to the south of Simrishamn in Skåne ^. 



Moberg, not without hesitation, refers this form to the same genus as 

 that of the Estland form Ohiiellus Mickivitzi F. Schmidt, for which Marcou 

 had proposed the new name Schmidtia'-. As this name was previousl}- 

 employed for another form it was subsequently changed b}'- Moberg into 

 Sclimidticllits '^. 



Moberg emphasizes the fact that Sc/imidlielliis / Torclli, with its long 

 horizontal spines, exhibits a certain analogy with both Mesonacis Vermou- 

 tana and with Schm. Michwitzi. Neither the Estland form nor the Swedish 

 form, however, in Moberg's opinion can be referred with certainty to the 

 genus Mesonacis. It is also quite uncertain whether the Swedish form can 

 be referred to the genus Schmidticllus, the geno-type of which is Sclmi. 

 Mickwitzi F. Schmidt. However, it is quite conceivable, or in any case 

 possible, that Sc/im. Mickicitzi and the Skåne form mentioned above may 

 have been quite nearly related, and could have belonged to the same genus, 



Walcott in his latest work arrives at the result that both forms in 

 all probability belong to the genus Mesonacis. 



As both forms are still quite imperfectly known, however, it is not 

 possible at present to make any definite conclusions regarding their rela- 

 tionship. In my opinion it is highly probable that they are much closer 



1 Sveriges äldsta kända Trilobiter. iGeol. Füren, i Stockholm Fürh. Vol. 21, 1899, 



pag. 33°'- 

 - American Geologist, Vol. 5, 1890, page 363. 

 3 Meddelande fran Lunds geol. laitklubb. Ser. B. Xr. 2, pag. 35. 

 * Olenellus & Other Gen. of Mfsonaridae. (Smiths Älisc. Coll. Vol. 53. Nr. 6. 1913, 



page 262 & 264 1. 



