Echinoid Tests, Diademoida. 
127 
by smaller tubercles in alternating series, there being one small tubercle immediately 
adjoining each main tubercle. In the adoral region, which comprises about 12 ambula- 
crals on each side, the main tubercles are twice the size of those in the adapical region, 
and each corresponds to tvvo ambulacrals. The appearance is as though every other 
main tubercle had grovvn at the expense of its neighbours and of the small tubercle on the 
same plate as itself, so that there novv remain only the alternate main tubercles and the 
alternate small tubercles, the latter belonging to those ambulacrals from which the 
main tubercles have been crowded out. The outer limbs of the ambulacrals remain 
quite distinct. 
The width of the perradial tract is 0.9 mm. at the widest place, and the diameter 
of one of the larger main tubercles is 0.5 mm. The height of an ambulacral in the 
same region is 0.26 mm. The larger main tubercles are clearly mamelonate and doubt- 
fully perforate. From the interporiferous area the ambulacrum slopes gently at first, 
and then more steeply. The tvvo podial pores are on the gentle inner slope. The outer 
slope becomes much more steep adorally. The outer limb of each ambulacral plate 
lies approximately at right angles to the perradius, and presents no conspicuous 
curvature. The pores are transversely oval. The inner one appears the larger, or at 
least the more clearly marked; it is bounded on its adapical margin by a ridge, and is 
separated from the outer pores by a slight elevation; but its adoral margin is depressed 
and a slight groove passes from it along the suture. For the rest the form of the pores 
and their surroundings is just as in a, except that the double scollops on the edge of 
each ambulacral are not clear. 
Relation s of the Specimen. — The same remarks as were made linder 
Ambulacrum a are applicable here. This specimen, however, is rather further from 
Triadocidaris and more Diadematoid in the development of its tubercles. 
Diadeinatoid ambulacrum, 7 . 
(Plate IX, figs. 218, 219). 
Material. — Fragment of an ambulacrum from the Raiblian beds of Jeru- 
zsälemhegy. 
Description ot the Specimen. — This consists of 7 more or less 
complete ambulacrals on one side, and 8 on the other. 
The perradial tract contains large, mamelonate, perforate tubercles, varying in 
size and arranged rather irregularly, three on one side and three alternating in position 
on the other. Each tubercle corresponds approximately to 2 ambulacrals (11g. 218). 
The space between these tubercles along the median line, as well as such space as 
may occasionally intervene between two successive tubercles, is hlled with granules. 
No sutures are visible in this portion of the ambulacrum. 
The two pores ot each ambulacral lie in a groove, which appears to extern! from 
the perradial tuberculate tract to the outer edge of the ambulacrum. The pores may 
therefore be described as conjugate. They appear to be transversely oval. These 
grooves lie approximately at right angles to the perradius. There is no slope on the 
inner part of the poriferous tract, but the outer part slopes slightly. 
