a ea a Echinoid Tests, Cidaroida. 95 
Material. — So far as plates of the test are concerned, we have the following 
isolated interambulacrals: from Jeruzsalemhegy, six lettered a, b, c, d, e, f, and a 
seventh on matrix and rather doubtful, lettered g; from cutting I on the Veszprém- 
Jutas Railway, three lettered h, 7, k. All these are Raiblian. The holotype has to be 
selected from among the radioles. 
Description of the Specimens. -. The plates being remarkably thin in 
proportion to their area, only the two smaller ones, d and e (figs. 173, 175), retain 
their complete outline, and even in them it is rather doubtful. Apparently the larger 
plates (a, f, h, k) were essentially five-sided, the upper and lower margins being parallel, 
the adradial margin approximately at right angles to them, and the two other sides 
of unequal length, meeting at an angle to form the margin of the zig-zag interradial 
suture (figs. 164, 178, 184, 187). Plates b, c, and 7 may have been five-sided, but 
owing to fracture the evidence is incomplete. The smaller plates on the other hand 
(for instance d, e) appear four-sided, although this may be due to the diminution of 
one of the interradial sides without its complete suppression. Their upper and lower 
margins are parallel, the adambulacral margin cutting them at an angle, which 
presumably increases in slope the nearer the plate is to one or other pole. The 
single interradial margin likewise cuts the upper and lower margins at an angle, 
but the direction of the slope presumably depends on whether the plate belongs to 
the oral or aboral hemisphere. Plates of this shape are more likely to have occurred 
near the poles. 
The sutural margins of the interambulacral plates appear to be constituted 
thus. Of the upper and lower margins one is bevelled underneath (fig. 166), while 
the other is either bevelled off on the outer surface, or bevelled in such a way that 
the bevel does not reach the outer margin but meets a ridge which turns it into 
a groove (fig. 165). For reasons fully given under Miocidaris (pp. 86—88), in the 
absence of evidence to the contrary, the margin bevelled underneath is regarded as 
the upper or adapical margin in the present species. In specimens a, }, e, f, h, & k 
the left-hand margin appears to be the adambulacral; it is bevelled underneath at 
a gentle slope, which, at least in a, e, and 7, appears to end on the inner surface 
against a slight ridge parallel to the margin (figs. 167, 168, 174). There are no traces 
of denticles in the specimens from Jeruzsalemhegy, but 7 and k show some almost 
imperceptible traces. The parallel ridge, though less conspicuous than in Triadocidaris, 
may still have Served to check the interambulacrals from sliding too far over the 
ambulacrals. The adradial margin was on the right in 7, and perhaps in d; in c 
its position is uncertain. In a, f, 7, & k, where the adradial margin is best preserved, 
it follows a curved or wavy course, similar to that shown in Tornouist’s figures 
of Archaeocidaris (1896, p. 47, & pl. IV, ff. 6 & 7); it is also clearly scolloped, and 
the notches indicate that in f there were about 7 or 8 ambulacrals to the plate 
(fig. 180). In d and e the interradial margin is single and is vertical. In a this 
margin was probably bent so as to form two sides; of these the only one preserved 
is vertical. In b, h, and k, where there also seem to have been two sides, each of 
them is bevelled in the same manner as the adjacent transverse margin (fig. 183). 
The primary tubercles. — The centre of the mamelon generally lies a little below 
half the height of the plate, and usually rather nearer to the interradial than to 
the adradial margin. Its position varies, as may be seen from the table of measure- 
ments. The mamelon is relatively small, its transverse diameter in a being 0.13 that 
