1916. No. 10. THE LOWER CAMBRIAN HOLMIA FALNA. 69 



and 9. The tïrst represents a young specimen, 30 mm. long, and the 

 second an older one about 60 mm. long. 



There are in addition other factors that indicate that there have existed 

 comparatively narrow and comparatively broad specimens even of the same 

 size. I Cf. fig. 4, pi. \'III). On account of differences of pressure in the 

 shales, however, the above relationship is difficult to demonstrate. 



Observations. As will be seen from the above, I have been able 

 in several respects to supplement and also in certain matters to correct 

 Holm's description of this the most important of all our Mesonacid forms. 

 This is owing both to my having more extensive material at my disposal, 

 and also because there were several cranidia that were unpressed or 

 only slightly so. In addition. Holm like other earlier authors confused 

 specimens of Kjenilfia lata with Holmia Kjenilfi. Holm's observation on 

 page 9 that the spine of the occipital segment diminishes in size with 

 increasing age, so that in the case of very large specimens it is very low 

 and wart-shaped, thus refers to specimens of Kjenilfia lata. His remarks 

 also regarding the spines on the first four thoracic segments in two very 

 large specimens (page 17) and as to the shell sculpture in one or two 

 rather large specimens page 17 are also to the same effect. 



The same applies to the remarks of Brøgger concerning the alterations 

 of the cranidium with increase of size. 



The size of the dorsal spines also now appear in a different light. It 

 is true that Holm states that some of them are rather long, but unfortuna- 

 tely his beautifully constructed figure, which have been produced very 

 often as the type of the Holmia genus, in this respect are quite misleading, 

 the spines being too thick and of quite uniform length. I refer to my 

 reconstructed figures 1 text-figs. 8-9 1. 



In correcting this matter the points of resemblance in Moberg's Sclnnulti- 

 ellus Torelli are still more prominent, so that as I pointed out on page 58 we 

 must assume that this form approaches very closely to Holmia even though 

 it may represent a type that must be differentiated into a special and 

 closely related genus. 



The Estland Schmidtielliis Miclnvitzi Fr. Schm. may also possibly be 

 included in the same classification (page 581. It is however very probable 

 that the form described in this work as Holmia grandis nov. sp.. but un- 

 fortunately very imperfectly known, belongs to this genus. 



Occurrence. Holmia Kjenilfi is one of the most common tossils 

 in the Holmia shales at Temten and we possess a very large number, 

 particularly of more or less complete cranidia. Whole specimens however 

 are not common. As we are also acquainted with a number of stages 



