236 G. H. Girty—Triticites. 



sected fluted partitions, the direction of which .is seldom the 

 same as that of the section. In longitudinal sections of Triti- 

 cites there extends along the axial line a band of anastomosing 

 walls, sometimes constituting a more or less regular network, 

 but usually disordered and confused. Aside from this the 

 space between the concentric walls over the median and larger 

 portion of the volutions is uninterrupted, except as some 

 irregularity permits the section to cut one of the longitudinal 

 partitions. Fig. 2 represents a longitudinal section through 

 Triticites secalicus. The undivided chambers are well shown 

 in this section, and the wrinkled partitions near the ends of 

 each chamber, which by their recurrence produce a band 

 through the axis. This difference in longitudinal section 

 would probably escape no trained observer, but its significance 

 can be appreciated only when interpreted in terms of the com- 

 plete organism. 



The minute wall structure of Triticites, though it does not 

 seem to differ from that of Fusulina, deserves to be noticed. 

 The wall in these shells is composite, apparently consisting of 

 two substances^ of different character, or, at all events, of differ- 

 ent density. Thus, when thin sections are examined, three 

 different .tints, with more or less well-marked boundaries, are 

 seen, namely, the transparent calcitic filling of the chambers, 

 the translucent substance of which most of the wall is com- 

 posed, and an outer opaque layer whose distribution will be 

 described somewhat carefully. This opaque layer is much 

 thinner than that which is translucent, and seems to represent 

 merely an external coating upon the upper and front sides of 

 each chamber wall. It usually appears as a strong dark line 

 in thin sections, which defines the translucent wall of one 

 chamber from that of the next, and it forms a plane of dehis- 

 cence along which the chambers and volutions tend to sepa- 

 rate. A certain amount of variation is manifest by this layer 

 and its conduct in the partitions is different from that in the 

 revolving wall, an indication of individuality in these structures 

 of which there is further evidence. In the revolving wall it 

 occasionally happens, chiefly in local areas, that no intensifica- 

 tion of tint is seen along the outer surface, the whole wall 

 being practically uniform. In other instances an intensification, 

 occurs on the inner side nearly equal to that of the outer, but as 

 a rule, from which exceptions are but few, sections clearly show 

 a dark coating upon the outer surfaces of the revolving wall. 

 This layer is seen to be continuous from the revolving wall to 

 the partitions and it thus defines to the eye the limits of each 

 chamber from that adjacent to it. The growth of the shell is, 

 therefore, seen to be the result of a repetition of similar stages, 

 each of which consisted of a prolongation of the shell first in a 



