REPORT OF THE DIRECTOR I919 83 



w'th the original black calcareous mud, forming the matrix. The 

 fourth specimen shows only the banded side where ten color bands 

 can be discerned. 



These four specimens allow a number of observations, which bear 

 partly on the nature of the color bands and partly on the habits of 

 the creatures that made the shells. 



The color bands were probably originally brown, as they appear 

 now in three of the specimens. They are preserved only in that 

 color where the conch remained free for a time from the dark mud 

 that embedded the shells and became later filled by secondary white 

 calcite. Thus in the first specimen, only a segment (the uppermost 

 in the accidental position of the conch on the sea bottom) is filled 

 with white calcite, the rest with black calcareous mud ; the brown 

 lines are seen on this segment, on the other part of the shell only -is 

 black smooth shadows. The second specimen is entirely filled with 

 secondary calcite and retains the brown color lines in perfection. 

 The third is only filled with crystallized white calcite in the narrower 

 portion and the brown color lines are seen there. In the remainder 

 they are dark brown to black. 



The surface is, in all four specimens, provided with an extremely 

 delicate surface sculpture, consisting of intersecting, nearly equal, 

 transverse and longitudinal lines. These lines are so fine that they 

 are only visible under a strong lens and about twenty are counted in 

 I mm. 



Not wishing to risk any of the specimens on account of the brittle 

 nature of the crystallized calcite filling, we have not made any thin 

 sections. On the natural section of the first specimen the brown 

 band can be seen to extend about .i mm into the interior of the 

 shell as a dark-brown body, that thins toward the edges and extends 

 to the surface. When weathering sets in, the lighter intervals be- 

 tween the colored bands begin to be dissolved first, the darker bands 

 probably being protected by the insolubility of the pigment dis- 

 tributed there through the shell-substance. There result then the 

 fluted forms which have been made the types of'Orthoceras 

 strigatum by Hall. 



It is quite probable that this dark pigment belongs to the group 

 of the melanin pigments which, according to Oppenheim (1918, 

 p. 390), cause the dark coloring of numerous mollusk shells and 

 being not dissolved by water, alcohol, CLher and resisting even 

 rather strong acids are little destructible. It is this utter insolubilit}'- 

 in water which has secured for these melanin pigments the possibility 

 of being preserved even through long geologic periods. Chitinous 

 6 



