1915- î^O- 12. THE STROPHOMENIDA'E OF THE KRISTIANIA REGION. 59 



In plate XLI\' of Davidson's Monograph we find a series of illustrations 

 of 5. antiqtiata of specimens of different stages of growth, and also with 

 different appearance for equally sized specimens. The difference of out- 

 line is of minor importance, but more remarkable is the difference in 

 surface characters. The figures lo — 1 1 . representing rather long and nar- 

 row specimens, in the explanation of the plate called var. scobrosa, have 

 radiating ribs of equal size, one bordering on the other, without intervals. 

 In the relatively broad specimen fig. 3 the radiating ribs are situated at 

 very considerable distance, while in the intervals is indicated the presence 

 of surface irregularities of somewhat the same t3-pe as in S. (Rafitiesquina) 

 corntgatella. In the text, Davidson states concerning the surface markings : 

 'External sculpture variable in its details, but always radiated by either a 

 few or many coarse, thread-like often waving radii, with interspaces be- 

 tween them of greater or less breadth ; while a smaller and shorter riblet 

 occupies the middle of the interspace. The entire surface of the shell is 

 also crossed by strong, equidistant, scaly, prominent ridges, or imbricated 

 lines of growth.' 



In the present material there exist two tj'pes of shells, that both 

 probabh' should be included in 5. antiquata in Davidson's sense of this 

 term. They are however too distinctly different to be united. One type 

 is characterized by a surface ornamentation much like that found in the 

 Stropli. rigida, while the other has very coarse and equal, radiating ribs. 

 As the original 3'oung specimen figured by Sowerby shows a series of radi- 

 ating ribs with fairh' large intervals between each pair, it seems natural 

 to take as typical specimens of the term S. antiquata specimens like the one 

 depicted by Davidson in his monograph in fig. 3 (pi. XLI\'). 



Specimens fairly like this type are rather common in my material. 

 Such a specimen is depicted pi. X, fig. 9 in the present paper. However, 

 what is seen in this specimen is not the actual surface, which is worn, but 

 an inner layer of the shell substance and therefore a character that is 

 very distinctly seen where the surface is preser\-ed, is not seen in this 

 specimen, viz. the very fine radiating striae in the intervals between the 

 main ribs. To me the supposition seems very probable that a specimen 

 like the one depicted by Davidson does not show these fine ribs because 

 of a not perfect preservation. The similarity between that figure and the 

 Norwegian specimens with worn surface is at anj' rate striking 



Of this type of shell: rounded triangular, with a more or less devel- 

 oped sinus and fold, with main ribs at considerable internals, the latter 

 showing a series of short corrugations besides a number of verv fine 

 radiating striae, there exists a fairly large material, from stages 6 and 8. 



