12 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I3I 



that springs from the floor of the valve near the middle. This pillar 

 is much expanded longitudinally with free edges extending a short 

 distance posteriorly, but also anteriorly to a point about three-fourths 

 the length of the valve from the beak. The anterior extension appears 

 to be a long, broad-ribboned ring. The details cannot be ascertained 

 because this part of the structure is obscured by silicious material. 

 This is the pre-campagiform stage. 



Details of the cardinalia are clear in a specimen without loop meas- 

 uring 4.2 mm. in length (paratype (U.S.N.M. No. I24202d). The 

 floor of the notothyrium is thickened by ridges joining the crural bases 

 and the septum is now extended posteriorly to meet the center of these 

 lateral ridges (pi. 3B, fig. 13). The expanded anterior end of the 

 septum is free, but no other details are available. 



A specimen measuring 4.5 mm. in diameter (paratype U.S.N.M. 

 No. I24202g) is somewhat more advanced than the previous one. The 

 notothyrial cavity is now deeply concave, the lateral extensions thick- 

 ened and anteriorly excavated to simulate a hinge plate supported by 

 the median septum. The crural processes on the loop are well devel- 

 oped and are located just anterior to, the hinge plate. The descending 

 branches of the loop attach to the distal expanded end of the septum 

 near its dorsal extremity. The greatest change has taken place at the 

 free part of the septum, the anterior end of which is distinctly divided 

 by an incision in its anterior end and the remains of a ring mounting 

 the ventral edge is clearly visible. This is probably the frenuliniform 

 stage of development. 



A still more advanced stage, the terebrataliform stage, is shown by 

 a specimen 6.6 mm. in diameter (paratype U.S.N.M. No. 1242021). 

 The hinge plate is still deeply concave and the crural processes moder- 

 ately long. The septum is well developed and high but does not now 

 reach to the middle. The descending branches of the loop are broad 

 and are now extended far anterior to the end of .the septum. The loop 

 is nevertheless still attached to the distal end of the septum by two 

 short branches, but the septum does not extend anterior to its point 

 of contact (plate 3B, figure 17). The specimen does not preserve a 

 ring or ascending branch, but remnants of it are visible. 



The next specimen of the series is 7.6 mm. in length and slightly 

 less in width (paratype U.S.N.M. No. i24i9oh). The hinge plate has 

 become considerably shallower by anterad growth of a transverse 

 plate at its anterior end ; the crural processes are large and the branch 

 between them and the hinge plate is now nearly obsolete. The descend- 

 ing branches are free of the septum, but projections, which face in- 

 ward and represent the remnant of the septal attachments, appear at 



