1916. No. XO. THE LOWER CAMBRIAN HOLMIA FAUNA. 15 



Occurence: Obolclla rotnndata is the most common fossil at Tømten ; 

 a great number of specimens have been obtained from the shale, — always 

 as isolated valves that exhibit both the external impression of the shell 

 and the inner, frequentl}' in a remarkable state of preservation. It is found 

 less often in the limestone beds. One piece of strongly weathered sandy 

 limestone that was found in 1915, contains a number of this form, most 

 of the shells being those of 3'oung individuals (pi. I, figs. 9 — 11). 



It has also been found in the Hohnia shale at Kletten, and in limestone 

 concretions in the corresponding zone at Aasta in the neighbourhood of 

 Elverum. 



Remarks: As mentioned above, the Temten form differs in severa^ 

 respects from Walcott's species Obolella Mobergi, the description of which 

 was based upon specimens from the Lower Cambrian sandstone at Skåne. 

 However, the difference is not so great as we might suppose, if we com- 

 pare my description and illustrations with Walcott's in his monograph. 

 Professor Moberg kindly lent me for purposes of comparison various 

 brachiopoda from the Lower Cambrian of Skåne, including Obolella Mobergi 

 Walcott from the original localit}' Sularp. These specimens, which were 

 determined b}- Walcott, do not quite agree with Walcott's illustrations. 

 In particular, his illustration of the inner cast of the ventral valve (pi. L\', 

 fig. 3 c I appears to be unfortunate; the pedicel tube, especially, is drawn 

 much too broad and massive. In the specimens that I have seen from 

 Sularp the pedicel tube is somewhat massive, but not more so than in the 

 specimens from Temten. Thus this character does not differ so greatly 

 that for that reason alone we should be justified in making separate species. 

 Other differences, however, are also present" 



1. The size is more considerable in the Swedish form. Walcott men- 

 tions a length of 9 — 10 mm. and a breadth of about 9 mm. (see table 

 on page 14). This difference is naturally not of great importance. 



2. The contour of the shell is different, the Swedish form being more 

 elongated and more pointed posteriorly. The breadth, as Walcott 

 also mentions, is somewhat less than the length, whilst in the case 

 of the Norwegian form the proportion is reversed. 



3. The area is more strongly developed in the Swedish form; however, 

 this feature varies in the Norwegian specimens. 



4. The vascular sinuses in the ventral valve have not so curved a course 

 as in the Norwegian species, where as a rule the sinuses are markedly 

 curved and run parallel to the outer margin of the shell. Yet this 

 feature varies, and in some specimens may be much like the Swedish 

 form. 



