1 62 University of Texas Bulletin 



these also, gradually showing still one secondary lobe at each side 

 on a whorl with 7 mm. diameter, while on one of 5.5 mm. diameter, the 

 sides of the median saddle are almost entirely straight ; the whole hav- 

 ing a trapezoidal form with slightly concave sides. In the mature form 

 the external saddle is very high, broad at the base and narrow above. 

 Leaving out of consideration the secondary lobes, the whole saddle 

 has a triangular form. It is scalloped on each side by about four 

 secondary lobes, which cause the existence of slender secondary 

 saddles ; all those nearer the upper portion of the saddle end in phyl- 

 loid points, one of them forming the highest part of the saddle ; while 

 two more branch off, not quite at the same height, somewhat below 

 the upper end of the saddle. The secondary lobes become gradually 

 shorter nearer to the base, where they constitute only small indenta- 

 tions. In the very largest specimens (i 10-130 mm.) there are a num- 

 ber of rudimentary lobes within those mentioned, which do not change 

 the general character and only scallop farther the outside of the saddle. 

 The first and second lateral saddles are practically built on the same 

 plan as the external one ; they also end in a phylloid point, but the next 

 lower secondary saddles branch off at the same height. The same may 

 be said of the first two auxiliary saddles, while the third seemingly is 

 also similar to them, though its form could not quite be made out. It 

 lies on the umbilical wall. 



In smaller whorls the general outline of the saddles does not change, 

 although the secondary lobes become simple and are not more subdi- 

 vided by rudimentary saddles. In a specimen of about 10 mm. dia- 

 meter we still see the same number of saddles, but the number of se- 

 condary lobes on the external saddle is now reduced to two on each; 

 at a diameter of 7 mm. there are only four saddles visible — the ex- 

 ternal, two laterals and one auxiliary; but the general shape remains 

 the same. One half whorl farther back, the external saddle shows 

 only one slight adventive lobe on each side, while the other three are 

 simple. On specimens with a diameter of 4 mm. the external saddle 

 shows still a slight indentation on the side nearer to the umbilicus, 

 but all the four saddles visible are of about the same height. One- 

 half whorl farther back, the first auxihary saddle splits up in three 

 branches, the middle one of which is the highest. One half whorl 

 farther back, the side branches, especially the one nearer towards the 



